Basic Workholding Techniques

Basic Workholding Techniques

Hardinge Inc. One Hardinge Drive Elmira, New York 14902 Phone: 800-843-8801 Fax: 607-734-3886 www.hardingetooling.com

Introduction The "Basic Workholding Techniques" brochure is meant to be a resource for your tool box, your desk or your reference library. It contains basic material that will assist the new machinist or production engineer as well as the veteran looking for a source on practical workholding techniques. We hope that you find some new ideas to help you improve your productivity and make your job easier. If you find that we have omitted some material or if you have a better explanation of a particular process or idea, please let us know. A companion publication "Precision Length Control" (2285) will help you with length control techniques related to draw-in collets and step chucks. We hope you enjoy "Basic Workholding Techniques".

NOTE: Information in this document is subject to change without notice. In no event will Hardinge Inc. be responsible for indirect or consequential damage resulting from the use or application of any of the information contained in this document.

Introduction The "Basic Workholding Techniques" brochure is meant to be a resource for your tool box, your desk or your reference library. It contains basic material that will assist the new machinist or production engineer as well as the veteran looking for a source on practical workholding techniques. We hope that you find some new ideas to help you improve your productivity and make your job easier. If you find that we have omitted some material or if you have a better explanation of a particular process or idea, please let us know. A companion publication "Precision Length Control" (2285) will help you with length control techniques related to draw-in collets and step chucks. We hope you enjoy "Basic Workholding Techniques".

NOTE: Information in this document is subject to change without notice. In no event will Hardinge Inc. be responsible for indirect or consequential damage resulting from the use or application of any of the information contained in this document.

Table of Contents

Basic Collet Introduction

CHAPTER 1 Basic Collet Configurations ........... ....................... ........................ ........................ ...................... .......... 8 Basic Collet Introduction Introduction ............ ........................ ....................... ....................... ........................ .............. .. 9 Head Angles ............ ....................... ....................... ........................ ....................... ....................... ...................... .......... 9 Lathe Collet Stationary Collet Tool Holder Collet Back Bearing ............ ........................ ........................ ....................... ....................... ........................ .............. .. 9, 10 Stationary Screw Machine Collet ............ ....................... ....................... ....................... ........... 10 Slot Design ............ ........................ ....................... ....................... ........................ ........................ ............... ... 11, 12 Straight Relief Hole Tear Drop Relief Double Slot Angular Zig-Zag Reverse Tear Drop (Over-The-Shoulder Collet)

Collet and Closer Systems

CHAPTER 2 Draw-In Collets ........... ...................... ....................... ....................... ....................... ....................... ................. ...... 14 Push-Out Collets ........... ...................... ....................... ....................... ....................... ....................... .............. ... 15 Push Sleeve (Stationary) Collets ............ ....................... ....................... ....................... ........... 16 Toolholder Collets ............ ....................... ....................... ........................ ....................... ...................... ...........16 16 Actuating the System ........... ....................... ....................... ....................... ....................... .................. ....... 17 Air-Operated Mechanical Closers ............ ....................... ....................... ................ .... 17, 18 Pneumatic Closers ............ ........................ ....................... ....................... ........................ ............... ... 18, 19 Hydraulic Closers .......... ...................... ........................ ....................... ....................... ....................... ............. .. 19 Machines Using Various Systems ........... ....................... ....................... ...................... ........... 20

Types of Collets

CHAPTER 3 Types of Collets ........... ....................... ....................... ....................... ....................... ....................... ............... ... 22

Concentricity and Spread

CHAPTER 4 Spindle Concentricity ........... ....................... ....................... ....................... ....................... .................. ....... 25 TIR Spindle ........... ...................... ....................... ....................... ....................... ....................... ...................... ...........25 25 TIR Back Bearing ........... ...................... ....................... ....................... ....................... ....................... ............. .. 25 Thread Run-Out & TIR ........... ...................... ....................... ....................... ....................... ................. ..... 25 What is Spread ........... ...................... ....................... ....................... ....................... ........................ ................. ..... 26 Grind Outs ........... ...................... ....................... ........................ ....................... ....................... ........................ ............26 26 Cam Grind ........... ...................... ....................... ........................ ....................... ....................... ........................ ............27 27 Flat Grind ............ ........................ ....................... ....................... ........................ ....................... ....................... ............27 27 Extra Spread—Over Spread—Over the Shoulder Collets ........... ...................... ..................... .......... 28 Formula—Maximum Opening for Over Shoulder ........... ...................... ........... 28

Collet Hardness and Wear

CHAPTER 5 Advantages of Hardened Collets ............ ....................... ....................... ....................... ........... 30 Problems Caused by Improper Improper Hardness ............ ....................... ..................... .......... 30 What Causes Collets To Wear Out ........... ....................... ........................ .............. 30 - 33 Wear: Illustrations of Causes ........... ....................... ....................... ....................... ............31, 31, 32 Wear: Multi-Spindle Automatics Automatics ........... ...................... ....................... .................... ........ 31, 32 Other Causes for Wear .......... ...................... ....................... ....................... ....................... ................ ..... 33

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Materials Held by Collets

CHAPTER 6 Charts ..............................................................................36 - 38

Collet Capacity

CHAPTER 7 Chucking Diameter Chart ..........................................................40 Collet Capacities ....................................................................... 40 Collet: Correct Size ................................................................... 40 Oversize ............................................................................. 41 Undersize ........................................................................... 41 Extra-Extra Spread Collet .........................................................42 Four Split-Long Bearing ............................................................ 42 Angular Slotted .......................................................................... 43 Zig-Zag Collet ............................................................................ 43

Serrations

CHAPTER 8 Reasons for Serrations ............................................................. 46 Flat Serration ............................................................................. 46 Tap Serration ............................................................................ 46 Circular Serration ...................................................................... 46 Saw/Buttress Tooth Serration ................................................... 47 Diamond Serration ....................................................................47 Last Serration ............................................................................ 47 Hex & Square Serrated Collets ................................................. 47 Disadvantages .......................................................................... 47

Concentricity and Gripping Force

CHAPTER 9 Order Hole (Collet Bore) ........................................................... 50 Smooth Bore ............................................................................. 50 Serrated Bore ............................................................................ 50 Diameter of the Order Hole ....................................................... 51 Bar Work ............................................................................. 51 Maximum Grip .............................................................. 51 Ground Rod & Tubing .................................................. 51 Best Concentricity ........................................................ 51 2nd Operation Work ........................................................... 52 Best Concentricity ........................................................ 52 Results of a Large Order Hole ..................................... 52 Results of Undersize Collet .......................................... 52 Length of Bearing ...................................................................... 53 Short Bearing ............................................................................ 53 Split Bearing .............................................................................. 53 Extended Nose Collet ............................................................... 53 Number of Slots .................................................................. 54, 55 Micro-Finish of Order Hole ........................................................ 56 Cloverleaf Grind ........................................................................ 56


Expanding Collets

CHAPTER 10 Expanding Collets .....................................................................58 Preparing the Blank ...................................................................58 Reasons for Out-of-Round Blanks ...................................... 59, 60 Styles Spindle-Mounted ................................................................ 61 Basic Parts ............................................................. 62, 63 Work Locating Stops .................................................... 63 Advantages .................................................................. 64 Special Considerations ................................................ 64 Master Expansion Collets ................................................... 65 Parts .......................................................................65, 66 Collet Pads ................................................................... 67 Advantages .................................................................. 68 Special Comments ................................................. 68, 69 Small Diameter Work ................................................... 69 Other Styles ........................................................................ 69

Master Collets and Feed Fingers

CHAPTER 11 Major Classifications ................................................................. 72 Master Collets .....................................................................72 Advantages/Disadvantages of Master Collets/Pads ................. 72 Style S Collet ...............................................................72 - 74 Style S Pads ................................................................. 74, 75 Martin Collets ...................................................................... 76 Martin Pads ........................................................................ 77 CT Collets & Pads .............................................................. 78 CB Collets & Pads .............................................................. 79 New Britain Collets & Pads ................................................. 80 Standard Master Collets & Pads ........................................ 81 Manufacturing of Hex and Square Pads ............................. 82 Master Feed Fingers Style "B" .................................................................. 84, 85, 86 BX/DX Adjustable ............................................................... 87 AF Adjustable ............................................................... 88, 89 Style "A" .............................................................................. 90 Adjustable Feed Fingers Dial-Adjustable ............................................................. 92, 93 Squirrel Cage ................................................................ 94, 95 Stock Saver ........................................................................ 95 Solid Feed Fingers Standard Solid Feed Finger ................................................ 96 Brazed On .......................................................................... 97 Milled Through ....................................................................98 Bar Stock Puller .................................................................. 99

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Chucks vs. Collets

Bar Stock Pullers Parts Loading and Unloading

CHAPTER 12 Reasons For Selecting Chucks .............................................................................. 102 Collets ............................................................................... 103 Reasons for Switching to Collets ............................................ 103 Chucks Mechanical—Manual ........................................................ 104 Pneumatic ......................................................................... 105 Hydraulic ........................................................................... 105 Electro-Magnetic ............................................................... 106 Vacuum ............................................................................ 106

CHAPTER 13 Bar Pullers ............................................................................... 108

CHAPTER 14 Rotating Parts Loader ..................................................... 110, 111


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CHAPTER ONE S

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BASIC COLLET INTRODUCTION

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CHAPTER 1 Basic Collet Introduction

THREAD

HEAD ANGLE

KEYWAY

H A

FACE CAPACITY HOLE

R D I N G E

BACK DRILL S

L

STOP THREAD

I

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ORDER HOLE

M

BACK BEARING

THREAD RELIEF

BEARING LENGTH LENGTH

3 BASIC COLLET CONFIGURATIONS SPANNER WRENCH HOLE

DRAW-IN COLLET

PILOT DIAMETER

OVERALL LENGTH

STATIONARY COLLET

SLOT SEAL HOLE

SHOULDER FOR CAP BACK BEARING

PUSH-OUT COLLET

SLOT RELIEF

SLOT

HEAD ANGLE


Basic Collet Introduction The collet is a workholding device that grips the workpiece or tool in a machine tool spindle. The more common machines that use collets are lathes, milling machines and cylindrical grinding machines. The basic collet is illustrated on the previous page. The common names of the various parts of the collet are shown. The collet is pulled or pushed into a mating taper in the machine’s spindle or tool holder. As the collet is moved linearly, it closes down on the workpiece or tool. The collet continues to close until it can no longer move. The amount of force is determined by the closing mechanism such as an air closer, hydraulic closer, or mechanical closer.

THE HEAD ANGLE

10°

Lathe Collet Lathe collets generally have a head angle of approximately 10 degrees. When the head angle of the collet is less than 7 degrees it will have a tendency to stick (not open when the closing force is removed).

Stationary Collet High production machines use stationary collets. Their head angle is much steeper than lathe collets, usually up to 15 degrees. This helps eliminate sticking and aids in opening the collet.

15°

Toolholder Collet Toolholder collets are made with less taper (7 degrees and lower) which gives them greater holding power. Sticking is not as much of a concern because the collet is not opened and closed during the production cycle. 7°

BACK BEARING

SPINDLE ANGLE BACK BEARING

HEAD ANGLE

Probably one of the least (but most) critical factors in close tolerance machining is the allowance between the back bearing of the collet and the spindle. When the clearance is too great, the collet will pivot or shift when tool pressure is applied to the part, causing excessive runout. Excessive runout can be caused by a worn spindle back bearing or a worn collet back bearing. For more information see chapter 4, page 25.

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Items such as the headstock center have their back bearings held extremely close (.0002"), which minimizes the clearance, assuring the best concentricity.

When a collet requires an extreme amount of spread, as do most screw machine collets, the back bearing often develops a 3- or 4-point out-of-round condition due to the distortion caused by spreading. Because this condition can cause sticking of the collet, additional clearance is allowed on the back bearing of the screw machine collets.

Face of Spindle & Cap

Nose Cap Sleeve Back Bearing

Draw Bar

Collet Back Bearing

Labyrinth Seal Sleeve

Stationary Screw Machine Collet With the stationary screw machine collet, concentricity is more difficult to obtain because there is a sleeve clearance as well as a back bearing clearance. With this style collet, it is important that the face of the cap is perpendicular to the spindle and that the face of the collet is perpendicular to the back bearing and the head angle.


Slot Designs Lets take a look at the slots in a collet. There are slot variations. Some of the more common ones are shown below. The Straight, Slot with Relief Hole and Tear-Drop Slot are used to make the collet more flexible. Straight Slot

Straight-Slot The straight slot is the least flexible and is used for collets that have very little spread, such as lathe collets. "Spread" is the amount a collet opens beyond the size of the collet. A .500" collet may spread to .510" when the bore is measured. This measurement is taken with the collet outside of the machine.

Relief Hole

Slot with Relief Hole The relief hole is designed for flexibility in a collet requiring more spread than the straightslot shown above.

Tear-Drop Slot (Screw Machine Collet)

Tear-Drop Slot

Screw machine collets, which require considerable spread, use the tear-drop slot for maximum flexibility.

Double-Slot The double slot is used for small order hole collets where a standard slot would be bigger than the order hole. The secondary slot can be as narrow as .005" wide.

Angular-Slot

Double-Slot Angular-Slot

The angular-slotted collet is used when holding regular shaped polygons (hex, octagon, square, and triangles) on their corners, or outside diameter, instead of on the flats. The angular slot prevents the corners of the stock from falling into the slots.

Zig-Zag Slot The zig-zag slotted collet solves the same problem as the angular slotted collet but is used for stock under 1/4". The corners of small stock may fall into the slots of the angular slotted collet, making it impractical. Because of the high cost of the zig zag slot, always consider the angular slotted collet first.

Zig-Zag Slot

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Over-The-Shoulder Collets

When more flexibility is needed, such as when using the over-the-shoulder collet, not only is the tear-drop relief slot used but the wall thickness is also reduced. This practice will reduce the life of the collet but is necessary to be able to grip the part over a shoulder. Part of the requirement for greater flexibility needed for the over-the-shoulder collet can be achieved by increasing the number of slots. CAUTION: The amount the collet will open is controlled by the stroke of the collet closer.

Other Slot Designs Other slot designs, such as those shown below, are used for special applications.


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CHAPTER TWO S

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COLLET AND CLOSER SYSTEMS

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CHAPTER 2 Collet and Closure Systems

Collet Systems There are three different types of collet systems— the Draw-In, the Push-Out, and the Stationary.

Nose Cap Coolant Shield

Collet Back Bearing

Head Angle

Spindle

Draw Tube

Collet

Draw-In Collet The Draw-In collet is the most common and also the most accurate for holding concentricity. To close the collet, it is drawn into the spindle angle. The only moving part (other than the collet) is the draw tube. Concentricity depends on the accuracy of the spindle and the collet. The order hole of the collet must run concentric with its head angle and back bearing which also must be concentric with each other. There are no other factors involved.


Spindle

Back Bearing

Nose Cap

Push Bar

Labyrinth Seal

Push-Out Collet The Push-Out collet is becoming obsolete. In the past, it was used in many manual turret lathes. To close the collet, it is pushed against a cap which is threaded or bolted to the spindle. The cap has an internal angle which mates with the front angle of the collet. The collet is closed by a forward force from the push tube. There are several items that affect concentricity: the collet, the spindle and the cap, along with its locating shoulder. All of these items require a tolerance when being manufactured. It is the build up of these tolerances which effects the total concentricity and accuracy of this system. Other items that affect concentricity are worn caps and caps that are not square with the face of the spindle.

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CHAPTER 2 Collet and Closure Systems Spindle

Collet Back Bearing

Face of Spindle and Cap

Nose Cap

Draw Tube

Sleeve

Labyrinth Seal

Collet

Push Sleeve—Stationary Collet The Push Sleeve system is the only system that allows length control of the workpiece. This is possible because the face of the collet is located against the back face of the hardened spindle cap. The collet is closed with a sleeve which pushes against the angle on the collet causing the collet to close, but not move longitudinally. Note: There are collets designed for part length control that are available for other collet systems. There are even more parts in this system to affect concentricity: the collet; the cap and how it aligns with its locating shoulder and thread; the sleeve with its allowance; as well as the clearance between the spindle back bearing and the collet’s back bearing. This system is the least accurate when trying to hold concentricity because of the large number of parts involved. Collet

Toolholder Collet Assembly The collet is closed by tightening a threaded cap on the tool holder sleeve. Drill Stop Cap


Actuating the System Each one of these collet systems require some means for opening or closing the collet. The following closing systems are used.

Mechanical Collet Closer Mechanical closers are used on manual machines. Because they require human intervention to operate them, they are seldom used on automatic machines. The exception is the cam-operated machines which still use a mechanical closer, but it is closed with a cam instead. Air-Operated Mechanical Closers are manual closers that have been fitted with an air cylinder to actuate them. These were common on the first Hardinge Automatic machines. They were eventually phased out for the totally air-operated closers.

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Pneumatic or Hydraulic Closers


Pneumatic and Hydraulic Closers

Pneumatic - Air The Pneumatic closer allows the light chucking pressures necessary when gripping thin-walled parts or tubing. When doing precision work, this system is most versatile. When doing extremely heavy stock removal work, the gripping pressures may not be adequate.

Disadvantages: Air is compressible, therefore any tool pressure that pulls on the workpiece could actually loosen the collet if its force is greater than the force created by the air pressure against the piston.

Hydraulic The Hydraulic and the Pneumatic closer systems look almost identical. The major difference is the pressure medium (hydraulic oil /air) and the higher pressures that are used. Hydraulic oil is not compressible, therefore any pressures opposite the piston force should not allow the collet to open. The pneumatic closer uses shop air pressure, usually 90 - 100 PSI, whereas the Hydraulic closer pressures can be as high as 1000 PSI. The same size piston used on a pneumatic closer will now deliver 10 times the force.

Disadvantages: Disadvantages include the added expense required for the hydraulic pump and sump. The hydraulic collet systems cannot be used for delicate or thin-walled parts. The pressures cannot be turned down low enough to eliminate crushing the workpiece.

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Machines that use the various collet systems

DRAW-IN COLLET: • • • • • • • • • • • • • • • •

Acme Gridley Cone Davenport Euroturn Gildemeister Greenlee Grinder Collets Hardinge Lathe Collets Mill Collets National Acme New Britain Schutte Tornos Warner Swasey Wickman

PUSH-OUT COLLET: Turret Lathes • Warner & Swasey • Jones & Lamson • Gisholt

PUSH SLEEVE - STATIONARY COLLET: • Brown & Sharpe • B. S. A. • Index


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CHAPTER THREE L

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TYPES OF COLLETS

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CHAPTER 3 Types of Collets

Types of Collets There are many types of collets available to the machine tool industry. Listed below are the styles available for 5C spindles. These same styles can be made for other types of collets.

1.

Fractional sizes

30. Extended-Taper Nose

2.

Decimal sizes

31. Emergency

3.

Number

32. Contact Lens

4.

Letter

a. Extended Nose Step Collet

5.

Metric sizes

b. Solid Extended Taper

6.

Special Accuracy (.0002" TIR for

c. Shank

5C collets only)

33. Solid Collet

7.

4-Split Long Bearing (Drill Collet)

34. Brass Collet

8.

Angular Slotted

35. Nylon Collet

9.

Zig-Zag Slotted

36. Morse Taper Collet - Female

11. Flat Face

37. Threaded - Solid - Order Hole 38. Threaded - Split - Order Hole

12. Taper Hole

39. Dead-Length ® Collet

13. Short Bearing

40. Dead-Length - Thru Hole

14. Long Bearing (5C ST & others)

41. Mill Arbor

15. Bearing Relief

42. Expansion Collet- Spindle

10. Angular Hole

16. Light Force

mounted

17. Heavy Duty

43. Master Expansion - Collet type

18. Stop Collets (SC)

44. Step Chucks

19. Blanks

a. Hardened & Ground

20. Serrated

b. Emergency

21. Hex

c. Extra-Depth

22. Square

d. Closers for all Step Chucks

23. Rectangular

e. Dead-Length Step Chucks

24. Special Shape & Extruded

45. Pin Step Chucks (Dead Length)

25. Octagon

46. Male Headstock Centers

26. Eccentric

47 Female Centers

27. Stepped

48. Driver Center

28. Plug Chucks

49. SURE-GRIP ® Expansion Collets

29. Extended-Nose

50. Dead-Length Step Chuck-Spider Stop


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CHAPTER FOUR L E D

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CONCENTRICITY AND SPREAD

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CHAPTER 4 Concentricity and Spread

0 0 0 1

.

1"

Concentricity Concentricity is measured by putting a gauge pin or ground plug in the collet order hole and measuring the Total Indicator Reading (TIR) of the pin’s runout with a .0001" dial indicator at a specific distance from the face of the collet. There are many factors to be considered when trying to achieve the best concentricity possible.

The Concentricity of the Spindle

1. TIR of the spindle angle If the spindle angle does not run concentric, it is impossible for the collet and workpiece to run concentric. Spindle Angle Back Bearing

Head Angle


1"

2. TIR and wear on the back bearing a. The back bearing must also run concentric because it will affect the concentricity of the collet. b. If the back bearing of the spindle is worn, it will allow the back bearing of the collet to pivot, which will cause excessive runout.

1"

3. Runout of the collet thread a. The thread must run concentric and square with the head angle and the order hole of the collet. b. If these conditions are not met, the pressures will be exerted on one leaf of the collet instead of all three. The parts manufactured with this collet will not be concentric with the chucking diameter. The uneven forces on the collet leaves may cause them to break.

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What is Spread? Spread is what puts the spring in the collet to help open it. This spring keeps the collet angle against the spindle angle, helping to eliminate chips which would cause runout. When the collet closer on a screw machine is opened, it is the spread in the collet that opens the collet so that the workpiece can be loaded or unloaded. Too much spread makes it harder to close the collet, reducing the gripping force on the workpiece. There is very little spread in a lathe collet, just enough to allow the workpiece to be loaded when the collet is opened. When a Brown and Sharpe style collet is not in the machine, the workpiece will very easily slide into the collet with plenty of room to spare. With other types of collets, such as lathe collets, a .003" (minimum) oversize plug will slide through the order hole (bore).

Screw Machine Collet - Large Amount of Spread

Lathe Collet – Very Little Spread

Grind Outs Grind-outs are collets that have been finished and are then re-ground to a new larger size. This process is used when a quick turnaround is needed. Maximum stock removal is 1/64" on case hardened collets. If more than a 1/64" is removed from the order hole, it will be softer than a standard collet because most of the case has been removed. There is no limit to grinding the ID when thru-hardening steel is used to manufacture the collet.


NEW COLLET-NO CAM GRIND

WORN ORDER HOLE - NO CAM GRIND

CAM and Flat Grind Screw Machine Collets, 16C, 20C, 25C Collets (5C collets and standard lathe collets are not cam ground) The cam grinding process helps reduce sticking problems. As the order hole of the collet wears, the collet is drawn further into the spindle seat. When this happens, the bearing area shifts from a full bearing to a bearing on the edges of the leaf (see above illustration). This edge bearing is most undesirable because it reduces the bearing (surface contact) between the spindle and the collet. To help alleviate this condition, collets are cam ground or flat ground (see illustration on next page). These two processes remove material from the slot area of the collet. This allows the collet order hole to wear and still maintain a bearing between the center of each leaf and the spindle angle. C

A M

CAM GRIND

F L A T

FLAT GRIND

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Extra-Spread Extra-Spread (Over-The-Shoulder) collets are used when gripping on a diameter that is smaller than the first area of the part which goes into the collet. These are commonly called Over-TheShoulder Collets.

There are restrictions on its use: • The collet closer must have enough linear stroke to allow the collet to open up sufficiently to clear the larger diameter. • The Davenport automatic, with the special burring attachment, uses pick-off collets which can handle a shoulder that is .100" larger than its gripping diameter. • Collet closers with a 1/2" stroke and a 10-degree spindle head angle may use a special collet which can handle a part with a shoulder approximately .150" larger than the bore. To find the amount that a special collet can open in relationship to the stroke of the collet closer, multiply the tangent of the collet head angle by the maximum closer stroke, then multiply the answer by 2. Don’t forget there will be some loss due to manufacturing tolerances.

EXAMPLE: 16C Collet = 2 (Tan 10 degrees x stroke) 16C Collet = 2 (.17633 X 5) 16C Collet = .1762" (maximum difference in diameters) Over-The-Shoulder collets are special collets which are custom designed and manufactured for each part or family of parts. They require special collet head angle designs, special slots and very precise heat treatment.


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CHAPTER FIVE L E D

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COLLET HARDNESS AND WEAR

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CHAPTER 5 Collet Hardness and Wear

Advantages of Hardened Collets Hardened collets have a longer life than collets not hardened

• • •

The harder the surface, the longer the life - wear resistance. Reduces the cost of running a job because fewer collets or pads have to be purchased. Reduces downtime because there are less collet changes.

PROBLEMS CAUSED BY IMPROPER HARDNESS • • •

Collets that are made too hard will be brittle and will break easily. When collets are not tempered properly will lose their spring. Collets that are too soft will wear out very quickly.

What Causes Collets and Pads to Wear Out? Poor housekeeping • Not keeping the collets & draw tubes clean. Take them out and clean them after each job. • Not using seals with screw machine collets. Surface condition of the material being gripped • Hot-Rolled Stock—it is rough with surface scale. The out-ofroundness causes irregular contact with surface of order hole. • Cast Bars—same as hot rolled stock. Types of materials • Abrasive materials shorten life—Aluminum, Cast Iron, Carbon and Ceramics.


Types of Machining Operations that may cause collets to break down:

Heavy stock removal and heavy drilling may cause push back.

Heavy forming-cross slide tends to open the collet. May cause stock to slip which would cause wear.

Forming and drilling at the same time.

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Types of Machining Operations that may cause collets to break down:

Intermittent cuts can cause radial slippage.

Out of Balance parts. Uneven pressure on the leaves.

All of the illustrated applications are common machining practices. Slippage can be overcome by using a properly designed workholding system which includes a collet that has the right head angle design, the proper serration and hardness, a collet actuating system with adequate draw bar force, a spindle drive system with adequate horsepower and torque, cutting tools that are properly sharpened and centered, and proper feed rates and spindle speeds for the tooling and material selected.


Other Causes for Wear Multi-Spindle Machines (Causes also related to single spindle machines)

•

The feed tube and the collet are not keyed together—this causes radial slippage when the collet opens and closes.

•

Crooked or bent bars put stress on one leaf of the collet or feed finger which causes slippage and loss of tension in that leaf.

•

Dirty bars create a very abrasive action between the bar and the feed finger and/or collet.

•

Bent feed tubes cause runout of bar and excessive wear on the leaves of the collet and feed fingers. The tubes are bent due to running bent or crooked stock and with considerable use.

•

Excessive tension on feed fingers. This is hard to check. You can push down on scale to check tension.

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notes: _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________


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CHAPTER SIX L E D

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MATERIALS HELD BY COLLETS

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CHAPTER 6 Materials Held By Collets

Materials Held by Collets MATERIAL

SPECS.

PROBLEMS

RECOMMEND

Steel Thru- hardening

None None

Standard Standard

HOT-ROLLED

Certain alloys can’t be cold drawn—hot rolling is less expensive than cold drawing

Stock is not round, diameter varies considerably and they have a very rough surface finish

Saw Tooth, Serrated, or 3-Jaw Power Chuck

COLD-DRAWN

Most common steel used for screw machine stock

None

Standard

Special-shaped stock (Made by drawing thru a series of dies in a semi-molten state)

In most instances cannot be held in a round collet—shape usually does not conform exactly to the print, therefore actual samples of stock must be sent with the order

Special-shape (Usually made using EDM methods)

COLD-HEADED

Part is cold-formed to near net shape—many are done from coil stock

Chucking diameters are not always accurate, out-of-round, etc.

Serrated collet or Power Chuck

SHEET METAL

Punched from flat stock

Size variation

Standard & Serrated

SHEET METAL EXTRUDED

Extruded thru several dies—such as a can shape

Size variations & thin walled

Standard, special-shaped & tapped hole

STAINLESS

There are many different kinds—magnetic, nonmagnetic, corrosion resistant, etc.—300 & 400 Series—some are hardenable and some aren't

Marks very easily

Standard & Serrated

CARBON STEEL TOOL STEEL

EXTRUDED


Materials Held by Collets MATERIAL

SPECS.

PROBLEMS

RECOMMEND

Made same as cold Darwin steel—we use Nickel Alloy-Dura bar— can be hardened to 42-45 Rockwell “C”

None

Standard & serrated

Made same as hotrolled steel

Scale, out-of-round

Serrated

Produces very fine grain iron—can be round or special-shaped

Variation of chucking area

Serrated and/or special-shaped

Permold and sand castings

Large variations— draft angle, rough surface finish

3-jaw power chuck, serrated

Cold-drawn bars

Easy to work— marks easily

Standard & serrated— nylon for highly polished stock

Near-net shape drawn through dies

Requires special shapes

Special-shaped —need a piece of stock 8" long to use as EDM electrode

BRASS CASTINGS

Sand casting process— die-type castings

Large variation on chucking surface, draft angles and rough surface finish

3-jaw power chuck, special-shaped & serrated

ALUMINUM BARS

Cold-drawn

Stock is abrasive— cutting tools wear fast

Standard

IRON COLD ROLLED

IRON CAST BARS IRON CONTINUOUS CAST BARS IRON CASTINGS

BRASS & BRONZE

BRASS EXTRUSIONS

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CHAPTER 6 Materials Held By Collets

Materials Held by Collets MATERIAL ALUMINUM EXTRUSIONS

ALUMINUM CASTINGS

ALUMINUM DIE CASTING

SPECS.

PROBLEMS

RECOMMEND

Near-net shape drawn thru dies

Requires special shapes—need a piece of stock 8" long which is used to make the EDM electrode

Special-shaped

Sand casting process— die type castings

Large variation on chucking surface, draft angles and rough surface finish

3-jaw power chuck, special-serrated collets

Much more precision than sand casting

Some variation on chucking surface, out-of-round, good finish

Special-shaped & sometimes serrated

Size variation, soft, marks easily— much of this material is slippery—requires light chucking pressure

Standard

Very brittle, will break if chucked too tight— powdery and abrasive— causes collets and the machine tool to wear out very quickly

Standard

PLASTICS: Nylon ® - Delrin ® Teflon ® - Bakelite ® Acrylic ® - Glassfilled - Synthene ® CARBON CARBIDE GRAPHITE CERAMICS

Comes in cast bars castings and molds


CHAPTER SEVEN

COLLET CAPACITIES

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CHAPTER 7 Collet Capacity

Chucking Diameter COLLET

ORDER HOLE

ACCEPTABLE BAR SIZE

FOR BEST CONCENTRICITY

ORDER HOLE GROUND TO

5C Standard

Fractional

+.002 to -.001

.001 Under order hole size

.001 under the order hole

5C Standard

Decimal

+.002 to -.001

Same as order hole size

Same as the order hole

16C Standard

Fractional

+.002 to -.001

.001 Under order. hole size


16C Standard

Decimal

+.002 to -.001



Screw Machine

Fractional

+.002 to -.001

.001 Under order hole size


Screw Machine

Decimal

+.002 to -.001



Master Collets

—

Hole size

Order hole

—

There are many discussions as to how much variation in stock size a collet can handle. Hardinge collet engineering has developed a chart (above) of suggested stock sizes that an order hole can handle. This refers to bar stock or chucking diameter.

Correct Collet Size When the collet is the proper size for the workpiece, there is full bearing along the angle and the circumference of each segment of the collet where they mate with the spindle angle (seat). The result will be good concentricity and excellent holding power.


Collet is Oversize If the collet is oversize as shown above, the part may pivot at the line of contact. The turned diameters may not be concentric with the bar or chucking diameters, and the machined diameters can be out-of-round. There will be line contact at the center of the leaf.

Collet is Undersize If the collet is undersize, the contact will be at the head of the head angle on the spindle angle and the order hole. This can help with bar push-back because the more tool pressure exerted on the bar the tighter the collet becomes. The part may pivot around the point of contact when excessive chucking pressure is NOT applied. The turned diameters may not be concentric with the bar or chucking diameters. The edges of the slots will bite into the workpiece and may cause damage or mark the bar.

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.050" Max.

Extra, Extra-Spread Collets The shoulder normally cannot be larger than the chucking diameter by more than .100" on the diameter. As the length of the bearing in the order hole gets shorter, the collet can be made to clear larger diameter shoulders.

G E

I N

D

R

A

H

Four-Split, Long-Bearing Collets Four - split collets are also called “5ST Collets” or “Drill Collets”. They come standard in various sizes for the 5C style spindles. Those with under 1/16" order hole are two-split. The various styles are: • • • •

Number sizes Letter Sizes Fractional from 1/64 to 1-1/16" (5C collets) Decimal (special order)


Angular-Slotted Collets These are special-order collets that are used to grip triangular, hex, square and other eccentric stock with corners that would normally fall into the slots of the collet. The angular-slotted collet has the following characteristics: • The slots are normally cut on a 7-degree angle instead of straight • The parts are gripped by the outside diameter of their corners • They are used for high production loading by eliminating the need for orienting the part with the shaped hole in the collet • Greatest use is for carburetor needle valves

Zig-Zag Slotted Collets These are special-order collets that are used to grip small diameter triangular, hex, square, and other eccentric stock with corners that would normally fall into the slots of the angular slotted collet. The zig-zag slotted collet has the following characteristics: • The slots are double-cut with the zig-zag EDMed (Electrical Discharged Machine) as the second slot • The parts are gripped by the outside diameter of their corners • They are used for high-production loading by eliminating the need for orienting the part with the shaped hole of the collet • The Zig-Zag overlaps even in the relaxed (open) position so that even the corners of the smallest stock cannot get into the slot • Expensive

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notes: _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________


CHAPTER EIGHT

COLLET SERRATIONS

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CHAPTER 8 Serrations

Serrations Why do we use serrations?

?

• Better gripping pressure by concentrating force in a smaller area • Reduces push-back of stock under the load of cutting • Reduces spinning or rotation of the stock • Under a heavy cut they may help prevent stock from "walking out" of the collet • Maximum contact area when gripping irregular surfaces such as hot-rolled & cast bars

Standard Flat Serration Increases gripping pressure but does not score the workpiece when using the correct closing pressure. This is the best all-around serration.

Tap Serration Tap serrations are used on pads with small holes that are impractical to groove and broach.

Circular Serration Circular serration is used to increase the gripping pressure but not bite into the workpiece as much as other serrations would.


Sawtooth/Buttress Serration The grooves and broach have the same shape as a buttress thread. This helps prevent both push-back and radial slipping of the workpiece. The sawtooth serration is the best design when doing heavy forming and/or drilling. This serration is designed to bite into the stock or workpiece.

Diamond Serration The grooves and broach have a 90degree “V” shape. This serration is designed to bite into the stock.

Hex and Square Collet Serrations Circular serrations are used on Hex, Square and Polygons.

Additional Information If the last serration is less than one full serration in length, the last groove will not be cut. This makes for a stronger area and eliminates chipping out of the serrations when loading bars.

Disadvantages of Serrations Serrations may score the stock or workpiece, and generally cost more than smooth pads or collets. Additional information in the following chapter.

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CHAPTER 8 Serrations

notes: _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____ _______________ _______ _______________ ______________ ______________ ______________ _______________ _______________ ____________ _____


CHAPTER NINE

CONCENTRICITY AND GRIPPING FORCE

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CHAPTER 9 Concentricity and Gripping Force

Chucking Surfaces The Order Hole The bore, order hole, or ID of the collet comes in many different surface finishes, diameters and bearing lengths. Let's take a look at these aspects.

Smooth Bore Most lathe collets are smooth bore. They achieve a full bearing on a finished part. They are typically less expensive than serrated collets and are used whenever the stock surface cannot be marked.

Serrated Bore Serrated Bore gives maximum gripping force when doing heavy machining operations. They are used for cast or hot-rolled stock which is usually out-of-round and has a rough surface finish. The serrations will bite into the material and reduce slippage and push back.


Diameter of the Order Hole For Bar Work

Small Order Hole The order hole should be smaller than the bar stock size for maximum gripping.

Exact Size or Slightly Under The order hole should be exact size when running ground rod or tubing. Decimal-size order holes are made to the exact three place decimal size.

Exact Decimal Size (3 decimal places) The order hole should be exactly the same size as the bar for best concentricity and least possibility for marking the stock. If you were running 1/2" stock, and needed best concentricity, but the stock actually measured .497, you should purchase a .497 decimal collet.

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Holding Power When Doing Chucking Work Exact Size For best results without marking, the order hole should be exactly the same size as the stock, resulting in: • Full bearing on chucking diameter • The best concentricity possible

Oversize When the order hole is larger than the chucking diameter, the following happens: • Less gripping force due to line contact at center of leaves • Diameter runout • Radial marks on the chucking diameter

Undersize When the order hole is smaller than the part chucking diameter, the following happens: • Distortion of the part • Diameter runout • Linear marks on chucking diameter BUT, the holding power will be greater.

For Best Concentricity When Holding Any Workpiece The order hole should be exactly the same size as the workpiece's chucked diameter.


Length of Bearing Short Bearing

• The smaller the order hole, the shorter the bearing length, mainly due to the length of the grinding wheel used during manufacturing.

• A short bearing would be used to clear threads on a part. The threads could be damaged with a standard collet.

• Special over-the-shoulder collets have very short bearings to allow for maximum opening with minimum collet stroke.

Split-Bearing (Bearing Relief) • Improves gripping pressure with the same amount of force. Many Davenport and Brown & Sharpe collets come standard with split bearings.

CAUTION: Extended-Nose Collets Extended-nose collets are used to extend the part out far enough to clear tooling interferences. This collet is easily damaged by applying moderate closing forces. Because the griping area of the collet is substantially forward of the head angle, the collet will bellmouth. This creates what is called a scissors grip on the part which is very unstable. Concentricity is difficult to hold using this style collet. Extended-nose collets should only be used for the lightest of cuts. If you need an extended-nose collet for normal machining, you're using the wrong machine tool.

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Number of Slots No Slots • • • • • •

Plug chucks and blank collets Used for arbors and fixtures Taper-hole collets - Morse, B&S Headstock centers Stub arbors Headstock mill drivers

Two Slots Two-slotted collets are used for special applications.

2 Split Drill 5CST

TWO SPLIT ANGULAR

Three Slots Three slots are most common. It is the most accurate design for centering a workpiece. They are usually used for Round, Hex and Square collets.

ROUND

SQUARE

HEX


Four Slots Four slots are used on larger collets to reduce closing pressure and are very common for square and rectangular collets.

SQUARE

HEX

RECTANGULAR

More Than 4 Slots More than four slots are used on larger collets to reduce closing pressure, for crimping collets, special collets and other special applications.

9-SPLIT

6-SPLIT Crimping

8-SPLIT

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Micro-Finish of the Order Hole (Bore) Machined—lathe bored Emergency style are usually bored by the operator. Special applications collets and brass collets are usually bored for the customer.

Grind Grinding is the most common method for finishing the order hole.

Lap—Hone—Polish • Extremely small collets that are too small to grind.

Extremely Small

• Stripper collets used to pull the workpiece off a die. • Capsule collets that require a very fine surface finish. • Workpieces that cannot be scratched. • Collets used on extremely high-speed machines where operating parts must be super-finished.

Stripper Collet

Capsule Collet

Clover Leaf Grind—Special Process The order hole is cleared at the slots using an end mill or grinding wheel. Chucking force is increased. Edges of the slots do not bite into oversized stock and they help eliminate marking on nominal stock. Used on hot-rolled stock.


EXPANDING COLLETS

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CHAPTER 10 Expanding Collets

Expanding Collets When doing secondary work, where extremely close length and concentricity tolerances are required, most of us hope that the part has a hole in it. It has long been known that using an expanding collet is the most accurate way to hold a workpiece. True, there are certain machining practices that have to be adhered to when doing the first operation on the workpiece. There are many different styles of expanding collets, each one having their strengths as well as weaknesses.

Preparation of the Blank Many people feel that as long as the part has a hole, it can be held accurately using an expansion collet. Unfortunately, this is not the case. When machining the bore, the section to be machined should not be inside the collet or under the jaws of the chuck unless it is round. If it is not round, there may be considerable distortion of the bore when it is removed from the workholding device.


If the outside diameter of a solid blank is out-of-round, and that diameter is chucked using a collet or step chuck, the bored hole will also be out of round after removal from the collet.

1. Out-of-Round Part (Collet shown open)

2. Rough Bore (Material flows into hole)

3. Finish Bore (Rounds out)

4. Collet released (OD returns to original shape and ID follows)

A precision bore is required when gripping the part with an expansion collet. Prior to boring the part, the outside chucking surface must be round within a tolerance that is less than the desired bore tolerance.

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BORE H

A R

D I N G E

S I

L

E

D

Z

E

O

M

1. Tubing or Drilled Hole

2. 1st bore not round due to uneven tool pressure

3. Finish bore truly round

When boring a part which will be held on an expansion collet, it should always be rough bored and then finish bored. When only one boring operation is done, the resulting hole will generally have the same out-ofroundness the blank or drilled hole had.

1. Blank ID out-of-round

2. Chucked ID forced round

3. Turned

4. Distortion after removal

If the bore to be gripped by the expansion collet is out-of-round, it will be forced round by the closing pressure. Any outside diameter turning work accomplished while being held by the expansion collet will be round until it is removed from the expansion collet. The bore will then return to its original out-of-round condition which in turn will make the outside diameters also go out-of-round.


By now you have probably gotten the message, “If you want to do precision work, while holding with an expansion collet, the bore you are locating on must also be a precision bore.” Work done on the outside diameters will not be any better than the tolerances and condition of the inside diameter being located on.

Styles There are many different styles of expanding collets. Let’s start out with a precision style, the spindle-mounted expansion collet assembly.

Spindle-Mounted Expansion Collet This system can only be used on Hardinge-style thread or taper-nose 5C spindles.

CAUTION: Do not use on Hydraulic Collet Closers with 5C spindle adapters. The assembly will be damaged and will be unsafe to use.

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Basic Parts of the Spindle-mounted Expansion Collet Locating Face

1. The Spindle Mount The spindle mount bolts, threads or is taper-locked onto the spindle nose of the machine. It has a locating face that is square with the spindle centerline. The collet is held in and adjusted to center with four adjusting screws. The screws are used to center the collet and force it against the locating face of the spindle mount to square the collet up.

2. The Collet

Locating Face

The collet is usually four-split, hardened and ground. The 5C-version can handle work with bores from 1/2" to 3". It has an ID taper which accepts a draw plug. The draw plug expands the collet as the draw collet is closed (pulled into the spindle). There is a locating face which must be perpendicular with the collet diameter.

3. The Draw Plug Assembly The draw plug assembly consists of the draw plug with an angle which mates with the collet’s ID angle. This plug mounts into a draw collet and is pulled pack by the collet closer. The draw collet does not have a head like a regular collet. Its only purpose is to center the draw plug in the spindle and to connect the collet to the collet closer. The clearance between the spindle back bearing and the draw collet’s back bearing is much less than a standard collet. This feature allows the assembly to hold part concentricities to within .0002" TIR. Draw Collet

Draw Plug


4. Machineable Work Locating Stop (Backing Plate) This part is bolted to the spindle collar and machined by the operator to conform to the locating point of the part. It gives greater stability to the collet and helps eliminate any flexing of the collet by supporting the workpiece. Two common problems when NOT using a backing plate are chatter and taper on the turned diameters which, many times, are caused by deflection of the collet.

Work Locating Stops for different applications

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Advantages of the Spindle-Mounted Expansion Collet • One of the most accurate expansion collets available • Gives dead length control, even without a backing plate • Can hold .0002" concentricity between the bore and turned diameters (the blank must be good to start with) • Can be used for large diameter work • Custom collets can be made with extra long bearings • Custom backing plates for complex datum surfaces • Longest life—hardened & ground • Soft blanks available for machine-in-place applications

Special Considerations • • • • •

Long set up time—10 to 30 minutes Requires skilled personnel Collet can be destroyed if collet is closed without a part on it 1/2" collets and above are guaranteed to have runout Special collets as low as 5/16" with a special draw plug and adapter can be easily destroyed by a careless operator, therefore, there is no guarantee on collets smaller than 1/2" • Collets are available to a 3/8" minimum diameter


Master Expanding Collet 5C & 16C collets—Collet-style

This expansion collet can be mounted in any machine or workholding device that uses 5C and 16C collets. It does not require a spindle mount. It mounts directly into the spindle and uses interchangeable pads which are machined by the operator to fit the part. These pads can be removed and saved for use on the same part at a later time. There are two exceptions to doing this: • The pads must go back on the same master collet in their original position • The TIR tolerances cannot be critical

Parts of the Master Expanding Collet

1. The Body The allowance between the body and the spindle back bearing is extremely close (much closer than a collet). This assures very close tolerance capabilities. The master collet is part of the body and is very large, giving extremely good stability. The leaves of the collet have holes threaded in them to accept interchangeable collet pads.

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2. The Draw Plug The plug is very large in diameter. This cuts down on the deflection normally associated with draw plugs.

3. Keyed Special Thread The draw plug is thread into this part. When the closer pulls back, this part goes back with it. The threaded part pulls away from the body which, in turn, pulls the draw plug against the collet angle, closing it.

4. Spring The spring pushes against the back of the master collet body keeping the head angle in contact with the spindle angle at all times. Without this spring, chips would get behind the master and cause runout of the master collet.


Master Collet Pads

Pads are made from steel (2" capacity) and aluminum (3" capacity). The steel pads are the standard pads. These pads are bolted to the master collet with six screws. A limit ring (the ring used for set up) is placed around them and the collet is very lightly closed, using just enough pressure until the ring cannot be turned by hand. The pads are then machined to the exact bore size. The 3" aluminum pads are for large diameter light work. They are bolted to the master collet leaves. Instead of a set ring going over the OD of the pads, there is a pilot on the front of the pads. A cap is placed over this pilot. The collet is very lightly closed and the pads are machined to the size of the part within a few ten thousandths. LIMIT RING

Hardened and Ground

PADS

For high production runs, hardened and ground collets should be used. When purchasing these collets, you must also purchase the master collet body. The pads will then be ground on that body, ensuring the best TIR possible.

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Advantages of Master Expanding Collets • Can be taken from the lathe to a milling fixture without the need for special spindle fixturing • For noncritical work, pads can be remounted without re-machining • Pads can be re-machined for a smaller diameter workpiece • Concentricity is excellent because pads are machined in place • Small hole chucking—.250" diameter to a depth of .250" • Part length control

Normal Slots in Master Pads

Pads held in step chuck for re-machining

Pads have been re-machined round

.100" diameter chucking is possible Hold the pads in the customer-bored step chuck and re-bore the back counterbore. This el iminates the space in the slots, allowing a smaller chucking diameter to be turned.

Special Comments—Scissor Gripping This type of expansion collet is designed for light chucking only for small diameter work. Scissor gripping of part may occur, especially when using 3" aluminum pads.

GOOD GRIP

POOR GRIP

Turned with set-ring to exact size of bore

Turned undersize or without set-ring


Special Comments—Small Diameter Work When doing small diameter work, overtightening the collet can permanently deform the pads. Heavy tool pressure can deflect the collet. The backing plate used with the spindle mounted expansion collet eliminates the problem.

1 1

SMALL DIAMETER Ratio 1 : 1

OVER TIGHTENING of small diameter work deforms pads

Other Styles of Expansion Collets Double-angle expansion collets Hydraulic expansion collets Hydraulic expansion arbors Push-style expansion collets

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notes: _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________

CHAPTER 11

MASTER COLLETS AND FEED FINGERS

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CHAPTER 11 Master Collets and Feed Fingers

Master Collets and Feed Fingers Master Collet Major Classifications Name Standard Masters Style "S" Martin Master CT (2 Holes in Pads) CB (1 Hole in Pad) New Britain Master

Feed Finger Classifications

Manufacturer All Hardinge Hardinge/Patented design Somma-Balas All All Obsolete

Name Style "B" Adjustable Tension AF Adjustable Dial Adjustable Style "A" Style "PB"

Manufacturer Hardinge Hardinge Hardinge Somma/Balas All Somma/Balas (Obsolete)

Standard Feed Finger Classifications Name Solid Feed Fingers Squirrel Cage Setters Spiral Slot

Manufacturer All All Setters

Master Collets Master collets are available for automatic screw machines, turret lathes and most of the newer CNC lathes. They were developed to reduce set up time. The collet no longer has to be taken out of the spindle of the machine when changing to another size bar. Most can be replaced from the front of the spindle, which only takes a few minutes. The standard master collet still requires the collet to be removed when replacing the pads. This style is not very popular, due to this requirement. The two major players are the Style "S" originally patented by Hardinge Inc. and the Martin Master originally patented by Balas. The following pages show illustrations of each style collet and pad along with the advantages and disadvantages of each.

Advantages of Master Collets over Solid Collets • Purchase masters only once • Pads are 60% less expensive than solid collets, while masters are roughly 30% more expensive than solid collets • Pads are available in different materials as a "special" • Pads are available in hex, square, and special shapes • Pads require less shelf space than collets • Many different machine masters use the same size pads • Emergency pads are less expensive than emergency collets • Hex and square pads are more accurate than hex and square solid collets


Style "S" Master Collet and Pad Features

There are no holes in the collet head angle, therefore no reduction of precision bearing surface. Also there are no tapped holes in the master collet.

Trouble-free dovetail anchor section

Pad has full bearing on the stock. No threaded holes through pads to reduce bearing surface. Dovetail

Independent clamp slides freely in and out of master collet. There are no threaded holes to get damaged.

Clamp Pad With Clamp

Independent clamp is a self-contained unit which slides into the master. The dovetail anchors pad in place.

Mating dovetails anchor the pad and clamp together independent of the collet. The clamp cannot be loosened by vibration.

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Collet

The Shoulder Takes the Thrust There can be no strain on the clamp or clamp screw due to impact of the bar striking the back of the pad. This is because the clamp is secured to the pad only. All of the end thrust is being absorbed by the pad shoulders in the recess of the collet.

Bar Stock

Pad

Front Shoulder

Rear Shoulder Bar Stock

Rear Shoulder takes Endworking Thrust

Collet Pad

Endworking tools exert a tremendous amount of pressure. With the Style "S" there is no strain on the clamp or clamp screw. The force is absorbed directly by the pad shoulders in the recess of the collet, thus affording positive pad location and accurate work.

The clamps stay with the collet when stored. Martin Masters require a set of clamps with each set of pads.

Additional Style "S" Advantages • No holes or slots in the head angle of the collet. This gives the collet maximum bearing surface between the spindle and head angle. • No uneven wear caused by holes and slots. High spots left after use of other masters will reduce head angle bearing when using solid collets. • No threaded holes in the collet to be stripped or damaged. • If clamp screw is stripped or damaged they can be removed without damaging the collet or the pad. • The pads are interchangeable without removing the master collet from the spindle.

Disadvantages • Clamps can come out of collet when being stored and are easy to lose. • Clamp screw threads and wrench sockets can be stripped due to overtightening.


Style "S" Pad Advantages • Easily inserted and removed without taking the master collet out of the spindle. • Pads gives maximum gripping surface no matter what size. • Dovetail anchor securely holds pads in place when bar is loaded. They cannot be dislodged. No other front-loading pad can make this claim. • No threaded holes in the pad that can be stripped or damaged. • Pads are available in standard sizes up to the rated capacity of the machine. • Available in round, hex, square and special-shapes to rated capacity of the machine. • Available in serrated or smooth to the rated capacity of the machine. • Available in English and metric sizes. • Available in the following materials: – – – – –

Hardened Steel Steel - Emergency Style Bronze Carbide Impregnated Nylon

• 60% less expensive than purchasing solid collets. • Hex and square and special-shaped pads run more concentric than solid collets. • Clamps not fixed to pads, therefore less storage area is needed for style “S” in comparison to Martin Pads. • Dovetail design pulls pads into the pad seat.

Disadvantages—none

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Martin ® Master Collets

The Martin Master has a slot in the face of the collet, through the head angle. The pad is held in the collet using a square lug that is threaded into the pad. Each lug has a taper-threaded lockingscrew which clamps the pad to the collet.

Collet

Tapered Screw

Pad

Clamp

Clamping cross section Advantages • The collet does not have to be removed to change pads.

Disadvantages • Loss of bearing surface when mated to spindle due to slots for clamps. • Uneven wear caused to the machine tool spindle due to slots in collet. This creates high spots on the spindle angle and causes solid collets to have very poor bearing to the spindle angle. • Clamping the pads into the collet may distort the head of the collet. • Clamps and pads loosen very easily. • Pads can be knocked loose when loading a new bar. • These collets not stocked in all sizes—may require a special order.


Martin ® Master Pads

Collet

Tapered Screw

Pad

Clamp

Clamping cross section The Martin Master pad has a square lug threaded into its side with a taper threaded hole in the lug for tightening it into the collet slot.

Advantages • Easily inserted and removed without taking master collet out of the spindle. • Clamps stay with the pads and cannot be lost.

Disadvantages • Machine capacity sizes are not available as standard pads because the clamp would protrude into the bore. Depending upon the machine, between 1/16" to 1/8" is lost from its maximum capacity when using these pads. EXAMPLE: Maximum size standard pad for a 1" Acme is 15/16". • More space is needed to store Martin pads because the clamp stays with the pad. • Due to the lack of popularity, the stock is not as complete as with the Style “S.” • When locked, they are not drawn back into the pad seat.

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"CT" Style Master Collets

Collet

Cone Point Set Screw

Pad

Clamping cross section Each pad is locked into the collet using two set screws (cone point) locating into detentes in the shoulder of the pad. The threaded holes are in the face of the collet. This collet was used as original equipment on National Acme machines. Advantages • Pads can be removed without removing the collet from the machine. Disadvantages • Tapped holes for locking screws can be damaged by overtightening which can destroy the collet. • Pads can be locked without the set screws being seated in the detentes on the shoulder of the pad. • When loading new bar stock, the screws take all the shock, causing the pads to loosen up. This allows chips to get behind the shoulder of the pad.

Pad Advantages • No clamps to lose. • Can be loaded without taking collet out of the spindle. • Pads can be easily stored because there are no clamping lugs. • Full bearing surface - no holes thru pads on large capacity sizes.

Pad Disadvantages • Flaring of set screw detentes due to over torquing of the set screws. • Can be dislocated when loading a new bar. • Expensive to manufacture due to special needs of set screw location area. • Subject to cracking and/or chipping if shoulder is not properly heat-treated.


"CB" Style Master Collets Collet Cup-Point Screw Pad

Clamping cross section The collet has one locking screw (cup point) per pad. The back shoulder has a back taper which helps lock pad in place. This collet was used as original equipment on National Acme Machines. Advantages • Front-loading collet does not have to be removed to replace pads. • Locking screws stay in the master collet—no clamps to lose.

Disadvantages • There is no way to make certain the pads are lined up with the set screw before tightening. • Tapped holes for locking screws can be damaged by overtightening, which can destroy the collet. • The screws take all the shock when loading new bars, causing the pads to loosen, allowing chips to get behind the shoulders. • Any misalignment of the screw or detente in the pad will cause it not to seat properly.

Pad Advantages • No clamps to lose. • Can be loaded without taking collet out of the spindle. • Pads can be easily stored because there are no clamping lugs. • Full bearing surface—no holes through pads on large capacity sizes.

Pad Disadvantages • Flaring of set screw detentes due to over torquing of set screws. • Can be easily dislocated when loading a new bar. • Expensive to manufacture due to special needs of set screw location. • Subject to cracking and/or chipping if shoulder is not properly heat-treated.

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New Britain Master Collet (O B S O L E T E)

Collet Cone Point Screw

Pad

Clamping cross section

The collet does not contain the lock screws. Two locking screws are in each pad which locks against a detente in the collet back seat.

Advantages • Front loading—collet does not have to be removed to replace pads. • No tapped holes in the collet.

Disadvantages • If the set screws are over-torqued, the collet can be permanently damaged. • The cutting pressure and load is against the set screws.

Pad Advantages • Locking mechanism stays with pads and cannot be lost.

Pad Disadvantages • Cutting thrust is against the set screws rather than the full back shoulder. • Some bearing loss due to holes for seals.


Standard Master Collet

Collet Locking Bolt

Pad

Clamping cross section

A screw goes through the head angle of the collet and into the side of the pad’s shoulder. The collet must be removed from the machine spindle to change the pads. These collets are available for all style machines.

Advantages • Once the collet is purchased, the pads are less expensive than solid collets.

Disadvantages • Must remove the collet to replace the pads. • The hole in the collet bearing angle causes uneven wear of the spindle. The resulting high spots make other style collets perform poorly. • Screw can be sheared when loading new bar stock.

Pad Advantages • Considerable savings over the price of solid collets. • Firmly held into the master collet.

Pad Disadvantages • Must remove collet to change pads. • Threaded holes remove bearing area on larger capacity pads. • Screws can shear when pad is hit when replacing bar stock.

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Hex and Square Pads Masters are Better Than Solids Hex and square pads run much more concentric than hex and square solid collets. If you are considering precision work and are going to grip on the flats of the hex or square stock, always use Style "S" master collets and pads. Solid collets will not run as true. Therefore, if the corners of your hex stock do not clean up all the way around the part, switch to a master collet with hex pads and they will clean up correctly.

The alternative to gripping on the flats of any polygon is to grip on the OD (corners) using either an angular-slotted collet or a zig-zag slotted collet (see chapter 1). The corners will not fall into the slots, making it easier to load the part and hold them concentric.


MASTER FEED FINGERS Chapter 11 Continued

Master feed fingers come in several styles from nonadjustable to fully-adjustable. The main reason for buying master feed fingers is to reduce expense as compared to the cost of solid feed fingers. The storage requirements for the pads are less than the area required for storing solid feed fingers.

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Style "B" Master Feed Finger

The Style "B" Master Feed Finger & Pads are the most practical feed finger for high production bar machining. The pads & feed finger design is the most stable on the market today. They were designed to take the abuse of your roughest operator and still give you the precision your machine tool requires. Below is a review of the Style "B" in greater detail. Style "B" Features:

No Screw or Pins to Hold Pads in Place

Three Pads Several Standard Shapes

PAD H

A

R D

I

BAR STOCK

N

G

E

PAD

Heat Treated for Tension Only Pad diameter controls different tensions

Full Bearing on the Bar Stock


Additional Advantages • Pads cannot come loose. • Quick changeover using Hardinge-designed wrenches. • Full bearing on the stock.

Disadvantages • Centrifugal force at high speeds can cause feed fingers to loose gripping force. • They are not adjustable.

Pad Advantages • Heat treated for hardness only. Maximum hardness possible which gives maximum life. • Cheaper than solid feed fingers. • Normally stocked in 1/64" sizes. Many decimal sizes are also stocked. • Pads stocked in round, hex, square. • Take up less storage space than solid feed fingers. • Special feed fingers are made for rectangular, other polygon shapes and extruded stock. • Pads come in many different materials.

Pad Disadvantages: None

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Materials Used for Standard Stocked Pads

Hardened Steel • Used for hot-rolled and cold-drawn steel bars. • Long wearing and reasonable abrasion. • Hard Pads—61-63 Rockwell “C” scale.

Nickel Cast Iron • Used for brass, aluminum, polished and plated stock—help eliminate scoring. • Greater life than bronze because they are harder. (If nickel scores, switch to bronze pads)

Bronze • Used for ground drill rod, brass, aluminum, polished and plated stock. These will eliminate scoring. • The best choice for stainless steel. • Only recommended when cast iron pads score the stock—bronze pads have a shorter life.

Nylon • Used on chrome-plated and highly-polished stock.


"BX" and "DX" Adjustable-Tension Master Feed Finger

Adjusting Sleeve

Body

Pad

The Style BX & DX feed finger has a sleeve that is moved to increase or decrease the tension on the pads. The sleeve locks against the feed tube. This feature eliminates the possibility of having it loosen up. The collet takes standard style “B” pads.

ADVANTAGES • • • • •

Tension can be adjusted. Adjustment is approximately 1/64" on diameter. Takes standard “B” pads. Positively locks against the feed tube. Loss of tension due to centrifugal force is reduced.

DISADVANTAGES • Only available for B&S 00, 0, DA2 and 9/16 Cone.

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"AF" Style Master Feed Finger

Adjusting Cap

Pads

Support Bushing

6 1 / 3 1

The "AF" Style Feed Finger uses inexpensive pads which are adjustable in 5 - 7 pound increments. The feed finger has a support bushing in the back to eliminate bar whip within the feed finger. No screws are used to hold the pads. They are adjustable for different tensions and stock sizes.

Advantages • Can adjust for different size stock—a full 1/32" adjustment from the rated size down. – Eliminates the need for decimal or metric pads and pads in 1/64" increments. • Feed bushings are used to control bar whip. – Eliminates feed hang ups. – Better finish on part because of less bar whip. • Adjustable tension on the stock. – More tension can be achieved using this feed finger than with any other feed finger produced, whether master or solid finger. – Extremely light tension for thin wall tubing and delicate stock.


Pad Advantages • Same master feed finger pads can be used for many different machines using the same style feed finger, which results in reduced inventory. • One tool cabinet drawer can hold hundreds of pad sets and still only weigh a few pounds. The same quantity of pads of any other type would take two or three tool cabinets, not just one drawer. • AF Pads are less expensive than style “B” pads, and much less expensive than solid feed fingers.

Pad Disadvantages • Cannot go under or over the rated capacity of the pad. For example, an AF6 pad for a 1" Acme feed finger has a minimum capacity is 3/8". If you wanted to feed a 1/4" bar, another style feed finger would have to be used. • Cannot go to the maximum capacity of the machine. • Pads will break when used without the support bushing. • Some people feel it is difficult to change pads. • The Model 3A AF pads cannot be used under 3/16".

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MODEL "A" MASTER FEED FINGER

The pads are held in a groove with a shoulder locating the pad on both ends. One key holds one pad in place which eliminates rotation of the other pads.

Advantages • No pins or screws used to hold pads into place. • Thrust supported by shoulders. • Pads less expensive than solid feed fingers.

Disadvantages • When loading bar stock, the pads can be knocked loose. • Pads are tricky to install.


notes: ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________

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Other Adjustable Feed Fingers Dial-Adjustable Master Feed Finger By Balas

Rear Support Bushing

Inner Master

Outer Sleeve

2 3 4

8


2 3 4

8

The dial adjustable master uses style “A” pads. It has a master body which accepts the pads. The body also accepts a rear support bushing. The outer sleeve is turned counterclockwise to adjust for more tension on the inner master. A wrench is required to spread the master collet for pad insertion. The same wrench is used to adjust the outer sleeve. There are numbers on the master body that indicate whether the tension is being increased or decreased.

Advantages • • • •

Tension is adjustable by hand. Wrenches are used to hold one member from turning. Carbide pads available for maximum wear resistance. Will not lose setting because feed tube locks against outer sleeve. Minimally affected by centrifugal force.

Disadvantages • Outer assembly must be removed to change pads in the master’s body. • Size restriction—maximum capacity of machine cannot be utilized. • The same problem as with all adjustable masters—too many pieces.

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Squirrel-Cage Feed Finger (Adjustable, but not a Master)

Whack it here with a hammer

ANVIL

Cross Section and Adjustment Method The squirrel cage-style feed finger has slots like a cage. They are swagged to size against an undersize plug and then heat treated.


Advantages of Squirrel-Cage Feed Finger • • • •

Inexpensive. Adjustable. Not affected by centrifugal force as much as masters with pads or solid feed fingers. No moving parts.

Disadvantages of Squirrel-Cage Feed Finger • • • •

Crude adjustment—“whack it” with a hammer. Concentricity problems after adjustment. Tension life is short. No precise way of telling what the tension is on the finger or a way to make certain that each leaf has the same tension.

Stock-Saver Feed Finger Whack it here with a hammer

ANVIL

ANVIL

Stock-Saver Feed Finger (squirrel cage -style) Same as the squirrel-cage but it has two adjustable areas—one in front and one in the middle of the finger.

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Types of Solid Feed Fingers

Standard Solid Feed Finger Advantages • No moving parts. • One costs less than a master.

Disadvantages • • • • • • •

Expensive if more than one is ever purchased. Non-adjustable. Tension controlled by heat treatment. Require finger for each size stock. Requires considerable storage space. Entire feed finger must be replaced when worn. Expensive because it requires additional feed tubes for each size stock.


FEED TUBE

BRAZE

FEED FINGER

Brazed On / In Style Feed Finger The brazed style feed finger is used when overcapacity stock is to be fed through an oversize collet. Instead of threads, there is a machined diameter. The feed tube threads are removed to the machined diameter on the special feed finger. The two are then brazed together. Advantages • Allows feeding of oversize stock not possible with standard feed fingers.

Disadvantages • Requires changing the "feed tube/finger" combination for each change in bar size.

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"Milled-Through" Solid Feed Fingers The "milled-thru" feed finger accepts rectangular, square and hex stock that has a thickness equal to the milled slot. One feed finger can do the work of several.

Example: When there are four different flat stock jobs to run, a feed finger or pad would be needed for each size. Suppose we have four pieces of flat stock: 1/4" square, 1/4" x 3/8", 1/4" x 9/16, and 1/4" x .744. When using a “milled-thru” 1/4" feed finger, all of these pieces of stock can be handled by the same feed finger with a considerable dollar savings. A 1/4" hex could be fed, but because of the small amount of bearing surface, feeding problems may result.


Round Shank Threaded Adapter

Feed Finger

Bar / Stock Puller—Feed Finger Style The feed finger style bar puller is used for pulling bar stock and also loading and unloading workpieces. Every size bar or workpiece requires a separate feed finger. See section on parts loading–chapter 14.

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notes: _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________


CHAPTER

12

JAW CHUCKS VS. COLLETS

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CHAPTER 12 Chucks vs. Collets

Chucks vs. Collets The collet and jaw chuck are the two major methods for holding workpieces or tools on a machine tool or fixture. Throughout the years, machinists have debated which was the best device for holding a workpiece or tool. Let's take a look at many of the different applications for each method of workholding. We will then finish out the chapter by describing each style of jaw chuck.

Reasons for Selecting a Jaw Chuck • Variation of chucking diameter greater than the collet's limits. • Parts too large for the collet capacity of the machine. • Eliminate large inventory of collets. • Machine does not have collet or step chuck capabilities. • Cost of a collet for a short run job. • Delivery time for a new collet for a short run job. • Rough chucking surfaces such as castings. • Non-symmetrical work requiring a 2- or 4-jaw chuck. • Customer has the facilities to machine chuck jaws for complex shapes but does not have them for machining collets.


Reasons for Selecting a Collet • Maximum gripping force—most critical on long overhang. • Life of a hardened and ground collet is much greater than machined chuck jaws. • Inexpensive precision workholding device—less expensive when using pads. • Special-accuracy collets are available in hardened and ground styles for super-precision chucking. • Collets are available in .001" increments (5C's). • Best TIR because there is no overhang. Most chucks extend from the face of the spindle between 4 to 6 inches, not counting the length of the jaws. • Centrifugal force does not cause problems with collets or step chucks that use closers. The working portion of the collet is completely enclosed and cannot expand at high spindle speeds. • Part tolerance or a long-run job dictate a collet to reduce downtime and the necessity to re-bore the chuck jaws. • Less chance of expensive wrecks.

One Shop's Reason For Switching to Collets One shop with two machines started out with jaw chucks on their CNC slant bed lathes. Within one year they had to replace the turret assembly twice, replace the spindle once, replace the jaw chuck twice, rebuild the jaw chuck three times, plus expend many man hours repairing the machines due to jaw chuck interference related wrecks. They then changed to collets and step chucks, which increased the gripping forces, decreased the overhang by 6 inches, increased their ability to hold close tolerances, and reduced spindle tooling interference problems, which eliminated major wrecks. Their down time was substantially reduced.

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Types of Spindle Chucks • Mechanical (manual-operated) • Pneumatic Pneumatic (air-operated) (air-operated) • Hydraulic • Electro-Magnetic Electro-Magnetic • Vacuum

Mechanical (manual-operated)

3-Jaw Universal

2-Jaw Universal

4-Jaw Independent

4-Jaw Universal

Pie Jaw

• Comes in many many versions—the versions—the most most common common are shown above. above. • Inex Inexpe pens nsiv ive. e. • Uses a key key wrench wrench to tighten tighten and and loosen loosen workpiece. workpiece.


Pneumatic (air-operated)

• Allows for lighter lighter gripping gripping pressure pressures s than hydraulic hydraulic chucks. chucks. • Smaller Smaller sizes can have accurac accuracy y very close to precision precision collets. collets. • Air cylinder is usually mounted at the rear of the spindle with a draw tube running through the spindle. • The air cylinder cylinder can also be part part of the chuck. chuck. This style chuck chuck is usually longer longer in length than the rear-mounted cylinder chuck which increases the TIR problems. This style is usually heavier, which puts more weight on the front of the spindle. • Some air chucks actually use the draw draw bar of the the collet closer. These These chucks usually have a thru-hole capacity equivalent to the collet capacity of the machine tool. • The internal construction of the chuck can restrict the the maximum RPM it can be run. run. • Precision air chucks usually usually cannot be run faster than 3,000 RPM. The exception is the small 3" air chucks which can run at 5,000 RPM or higher.

Hydraulic Chucks

• Much greater greater gripping gripping pressur pressures es than air air chucks. chucks. • The hydraulic hydraulic cylinder cylinder may be either either at the rear of the the spindle or built built into the actual actual chuck. • Thin-wall Thin-wall tubing and delicate delicate parts cannot cannot usually be run with hydraulic hydraulic chucks chucks because the chucking pressure cannot be reduced enough. • Weighs more more than air chucks chucks creating creating additional additional spindle spindle loads. loads.

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Electro-Magnetic Chucks • Normally used for flat magnetic steel steel and iron parts—if parts—if surface is flat, there will be no chucking distortion. • Expe Expens nsiv ive. e. • Cannot be used for nonmagne nonmagnetic tic materials materials.. • Requires Requires special special electrical electrical rotating rotating connect connection. ion. • Requires Requires a large power supply. supply. This type of chuck uses an electric-po electric-powered wered magnet magnet which consumes large amounts of DC (direct current) power. A power supply is required to change the normal AC (alternating current) to DC. Because of the amount of current that is required, a rather larger power supply is required.

Vacuum Chucks • • • • • •

Will hold all types types of material material with even chucking chucking pressure pressures. s. No distortion caused by chucking if the the chucking surface surface is not distorted to begin with. Requires Requires a separate separate vacuum vacuum pump. Expe Expens nsiv ive. e. Materials Materials to be be chucked chucked cannot cannot be porous. porous. There are universal rotary vacuum chucks that have vacuum ports that that can be turned turned off or on to conform to the chucking surface area. • There are special techniques for holding bandsawed blanks for the first operation.


CHAPTER CHAPTER

13

14

BAR STOCK PULLERS

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CHAPTER 13 Bar Stock Pullers

Bar Pullers There are several different style bar pullers on the market. The two most common are the feed finger style and the two-finger style.

Feed Finger Style The feed finger style consists of an adapter that fits in the machine's turret. The special feed finger threads into the adapter. These feed fingers can be acquired for all nominal sizes, usually from stock. The bar puller functions the same way that a feed finger works in an automatic lathe. When using a bar puller, the part has to be cut off approximately 1/2" from the face of the collet. The bar puller feeds onto the bar, forcing the fingers to spread apart. There must be enough tension on the fingers to be able to pull the bar out, after the collet is open, without slipping. A large diameter and/ or a long length of bar will require considerable tension.

Two-Finger Style The two-finger style is universal. One puller will handle stock from 1/8" to 1-5/8" and larger. This makes it less costly to use than the feed finger style. The unit can also be mounted parallel to the centerline of the spindle as well as perpendicular to it, and can be held in either a round shank or square shank holder.

Both Styles Feature • • • • •

Up to 1-5/8" stock. (Hardinge-brand bar puller) Can pull up to 12 foot bars when using a "non-pusher" type bar support. Inexpensive. Can pull short or long bars. Uses spindle liners for precision parts with no whip.

CAUTION: Stock should never extend beyond the end of the machine tool spindle unless supported with a “Non-pusher” style bar feed tube, or similar device.


CHAPTER 14

PARTS LOADING AND UNLOADING

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CHAPTER 14 Part Loading and Unloading

Parts Loading and Unloading Aids Let's consider that we have a good operator but we want to assist him to increase his productivity by reducing potential scrap due to human errors. These devices can be loaded by hand, but only if the machine functions have been completely stopped, per OSHA (Occupational Safety & Health Administration) regulations.

Feed Finger Style Parts Loader

Solid Tube Parts Loader Holds part with friction from the “O” ring. This device should be spring-loaded to hold the part against the shoulder in the collet as it is closing.


Rotating Parts Loader • • • •

Can load parts that are not round. Can load round parts without scratching. Requires special collet for each part. To load parts that are not round or parts that cannot be scratched, a special step chuck or driver plate is needed.

Parts Unloading Aid

Spring Ejector Stop A spring ejector collet is used to eject the part into a parts catcher. The parts catcher can be an air-operated parts chute. A wire basket held by the turret or cross slide. Many times these are arranged to automatically dump their contents at the return of the slide or index of the turret.

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Basic Workholding Techniques

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