CONTOUR ATTACHMENT FOR LATHE
SYNOPSIS A concave attachment attachment is a versatile one to cut cut concave-convex profiles. profiles. A set of rotating rotating plates plates have T-slots T-slots for the T-bolts that hold hold the boring bar. These These plates are rotated rotated by a train of gears. The bar is held roughly roughly yet free free enough to rotate. rotate. When the tool is built, the the boring bar is first first clamped with both both pivots at lead centre. So, the tool describes a zero radius when the crank is turned.
At this time, one set up pin hole is drilled in each of the rotating plates, as indicated so that the pin touches the boring boring bar. Then to set the tool, tool, for a desired radius, radius, it is merely necessary to place a piece of flat stock the same thickness as the desired radius radius between between the bar and the set up pins while securing securing the bar in position. position. At this point, data the flat stock and set up pin can be removed.
INTRODUCTION
NEED FOR ATTACHMENT
In recent years, new fabrication techniques have been developed to satisfy the technological demands. demands. Moreover, emphasis is stressed on attachments. attachments.
Attachments are used in various fields and machines depending upon the needs to be fulfilled fulfilled and mode of operation. operation. An attachment attachment eliminat eliminates es the purchasing purchasing of a new unit which serves serves the same purpose. purpose. For example, a lathe lathe occupies a place place opposite to that of a milling machine, the ten machines mainly used to produce cylindrical and plain surfaces respectively. respectively. By implementing an attachment attachment to a unit, the capacity capacity of the unit can be increased which is very economical.
WORKING PRINCIPLE
The worm wheel is is rotated with the help help of a worm shaft. Rotating plates with with Tslots slots that hold the boring boring are screwed to the worm wheel. wheel. The worm wheel wheel in turn is screwed to its base with with a simple gear train. The rotary motion is imported imported to the blank
The base plate is in ‘I’ shape with drilled holes to suit the gear stems. The compound reset that is locked solid with its base of the crosslide of the carriage is removed and in its place, the base plate is so designed to seat. The base plate’s axis is parallel to the lathe bed.
Rotating Plate:
The rotating plate is a primary part of the unit. It is circular in shape. It has ‘T’ slot along its diameter for the ‘T’ bolts that hold the boring bar. It is screwed with the help of Allen screws to the worm wheel, so that the direction of the rotation of the worm wheel and the rotating plate is the same. A set up in hold is drilled in the rotating plate to set the tool for desired radius.
handle is rotated; the worm shaft rotates the proportionate worm wheel. A seating is provided on the worm wheel to seat the rotating plate.
Spur Gear:
The spur gear is screwed between the worm wheel and the base plate. A step down bush is used to fit the worm wheel and the spur gear songly yet free enough to rotate.
Idler Gear:
The idler gear is screwed to the base plate by press fitting the idler gear and its stem to the hold provided in the base plate. The rotary motion between 2 spur gears is
component reset is removed and the blanks are bolted to cross slide of the carriage. The whole unit resets on these blanks.
Boring Bar:
The boring bar is held songly in the T-slots provided in the rotating plates by the T-bolts. The tool that cuts the radial is screwed to the boring bar. The boring bar moves over a certain radius when the crank is turned or rotated.
WORKING OF THE UNIT
When the worm shaft is rotated in a clockwise direction, the worm wheel rotates in the clockwise direction and vice versa.
The base plate is in ‘I’ shape with drilled holes to suit the gear stems. The compound reset that is locked solid with its base of the crosslide of the carriage is removed and in its place, the base plate is so designed to seat. The base plate’s axis is parallel to the lathe bed.
Rotating Plate:
The rotating plate is a primary part of the unit. It is circular in shape. It has ‘T’ slot along its diameter for the ‘T’ bolts that hold the boring bar. It is screwed with the help of Allen screws to the worm wheel, so that the direction of the rotation of the worm wheel and the rotating plate is the same. A set up in hold is drilled in the rotating plate to set the tool for desired radius.
of the worm shaft from base plate is the height of the worm from the base when the handle is rotated; the worm shaft rotates the proportionate worm wheel. A seating is provided on the worm wheel to seat the rotating plate.
Spur Gear:
The spur gear is screwed between the worm wheel and the base plate. A step down bush is used to fit the worm wheel and the spur gear songly yet free enough to rotate.
Idler Gear:
The idler gear is screwed to the base plate by press fitting the idler gear and its
blank connects the setting blank and the base plate. These blanks are so designed that the component reset is removed and the blanks are bolted to cross slide of the carriage. The whole unit resets on these blanks.
Boring Bar:
The boring bar is held songly in the T-slots provided in the rotating plates by the T-bolts. The tool that cuts the radial is screwed to the boring bar. The boring bar moves over a certain radius when the crank is turned or rotated.
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Round balls can be produced.
DESIGN OF SPUR GEAR
SPEEDS IN GEAR BOX:
Measured Specifications:
N1/N2
=
D2/D1
Where, N1 N2
= =
Motor speed in RPM---40 RPM Output speed
The spur gears, which are designed to transmit motion and power between parallel shafts, are the most economical gears in the power transmission industry.
APPLICATION:
•
Material handling
•
Feed drives
•
Machine tools
•
Conveyors
•
Marine hoists
INTERNAL SPUR GEAR:
The internal gears are spur gears turned "inside out." In other words, the teeth are cut into the inside diameter while the outside diameter is kept smooth. This design allows
•
Positioning
•
Rollers
•
Indexing
EXTERNAL SPUR GEAR:
Perhaps the most often used and simplest gear system, external spur gears are cylindrical gears with straight teeth parallel to the axis. They are used to transmit rotary motion between parallel shafts and the shafts rotate in opposite directions.
They tend to be noisy at high speed as the two gear surfaces come into contact at once. Internal spur gears: The internal spur gear works similarly to the external spur gears
Maximum bending stress Tb = (M * r) / I ……………….Eqn.1.1 Where, M is maximum bending moment on the shaft. r is the radius of the shaft. I is area moment of inertia of the shaft.
Design Procedure •
• •
•
Draw the bending moment diagram to find out the maximum bending moment (M) on the shaft. Calculate the area moment of inertia (I) for the shaft. Replace the maximum bending stress (Tb) with the given allowable stress for the shaft material. Calculate the radius of the shaft.
Shaft Design Problem
I = pi * r^4 *0.25 = 0.785*r^4………………..Eqn. 1.2 •
From Eqn1.1 we can write:
40 = (66666.67 *r)/ (0.785*r^4) r= 12.85 mm •
So, the minimum radius of the shaft should be 12.85 or 13 mm.
DESIGN OF IDLER GEAR:
Pressure Angle No. of Teeth (N)
= =
14 ½° 25
Depth of Cut (or) Tool depth =
( 2.157 /DP ) x 25.4
=
( 2.157 / 18 ) x 25.4
=
3.044 mm
=
( 1.157 / DP ) x 25.4
=
( 1.157 / 18 ) x 25.4
=
1.633 mm
=
20 mm
Dedendum
DESIGN OF WORM SHAFT:
Outer Diameter
TO FIND ANGLE AND LEAD:
{ Lead / ( PCD x T) }
Lead
=
pitch x No. of Start 0.250 x 1
Lead
=
0.250
Angle
=
{ 0.250 / ( 0.628 x II ) }
=
0.250 / 1.9741818
=
7° R.H
Where, ( 0.628 x II = 1.9741818 ) Angle
To milling machine held is tilted at an angle of 7¼° R.H
DESIGN OF WORM WHEEL:
Bore Diameter No. of teeth Pitch circle diameter
Throat diameter
Tip diameter
= =
25.4 mm 42
=
No. of teeth x module
=
( No. of teeth + 2 ) x 2
=
( 42 +2 ) x 2
=
88
=
PCD + 2 module
=
88 + ( 2 x 2 )
=
92 mm
=
Throat diameter + (1.5 module) (
)
ASSEMBLY
A train of simple gears is press fitted to the base plate by bushes. These gears are hence held singly. Yet free enough to rotate. A worm wheel is screwed to one of the spur gear a circular blank is screwed with the help of Allen screws. A worm shaft is fitted to the base plate with the help ‘L’ clams.
This worm shaft in engagement rotates the worm wheel. Rotating circular plates are screwed to the worm wheel and the circular plates are Allen screws. Seating is also provided on the worm wheel and the circular blank to hold the rotating plates. The rotating plates have T-slots for T-bolts that secure the boring bar. Setting end connecting
lathe as per the drawing specification. A press fit is obtained on the town portion of the bush by choosing a shaft hole combination of H7 P6.
5. Idle Gear Bush:
Similar to the other bush the same tolerance range is observed on 30 x 351 M.S. rods and the bush is turned lather. A press fit of P6 tolerance is closely maintained to enable the location of the idle gear.
For a pitch of 0.250” and 90.50 OD the lead, depths of cut are calculated. For these design values the worm gear is cut on a milling machine using to form relived cutter.
The marking of the step down bushes with the worm gear is checked beforehand. For a 35mm shaft combination a bore of slightly less in size is made on the worm wheel blank to obtain a press fit. Once the seating is aer, four tapes are done on the outer face of the worm wheel blank to grip the rotating slot firmly (by means of Allen screw)
7. Spur Gear:
8. Rotating Plates:
C.I. of 1 x 44.02 mm is turned on a lathe to suit the boss of the making parts. For holding the boring tool T slot of 3/8” is done on a slotting machine using a key way slotter. 9. Bearing bar:
The boring bar is fabricated in mild steel. It has a T slot to suit the T bolt. The T slot is machined in a slotting machine with the help of a T slot cutter. It has screws provided at the side of the slots to tighten on loosen the tool that is placed in the slot.0
used as the chief lubricant since it’s a nonconductor of heat thus achieving temperature limitations.
Maintenance aids to good precision, longer life and higher efficiency. following precautions should be followed:
1. Proper handling is necessary to avoid the teeth damage in the gears. 2. Periodic lubrication is necessary to avoid film formation. 3. On any account there should not be any novelty in gear blanks 4. While machining, proper dead centre should be maintained. 5. The axis of the unit should be always paralleled to lathe bed.
The
