Design Guideline For Collets
INDEX Introduction/ Index 1
Clamping di diameter of co collet
2
Other data
3
Slit Slits s (num (numbe berr ,widt width h ,f ,fla latt tten enin ing) g) Types of component & slits position Slits (length of slits & collet wallthickness) Slits forms
4
Collet exapansion values
5
Free bore details
6
Longitudinal gr grooves
7
Gripping bore
8
Type of collets
9
Material used for collets
10
Heat treatment
11
Col Collet ex expansion (p (process) ss)
12
Sepc Sepcia iall manu manufa fact ctur urin ing g inst instru ruct ctio ion n
13
Calcu Calcula lati ting ng cla clamp mpin ing g force force gene genera rate ted d in colle collett clamp clamping ing
14
Checking of collets
15
Typica ical dr drawing of of co collets Traub A Fortuna HMT ASH 160 HMT TR 42
Design Guideline For Collets Page 1 1 Clamping Clamping dia for standar standard d collets collets On the finished drawing , the maximum clamping Ø for any size is specified It is to be noted that for automatic collets the max through hole depends on the max clamping Ø of the concerned feed finger (feed collet ) 1.1 Collets should not be used for diameter > 0.1 mm than the max. diameter for which it is to be designed 2 Other data data on all finished finished as per following following fig. fig. 1
fig 1 3.1 Slit: Number Number , Width ,Flatteni ,Flattening ng see fig.2
Shaft Ø D from upto 20 20 30 30 40 40 50 50 60 60 80 80 100 10 0 12 0 12 0 15 0 *
collet with shaft Ø D≥3/4 L Ø□ Hex Oct 3 3 4 3 3 4 3 3 4 4 3 4 4 3 4 4 6 4 4 6 4 6 6 8 6 6 8
Collets for clamping Ø
collet with shaft Ø D ≤ 3/4 L Ø□ Hex Oct 3 3 4 3 3 4 3 3 4 3 3 4 4 3 4 4 3 4 4 3 4 4 3 4 4 6 8
Breadt Flattening on h taper length b B 1* 3 1. 2 4 1. 6 5 2 6 2. 2 7 2. 5 8 3 10 3 .5 12 4 12
Design Guideline For Collets PAGE 2 3.2 Types of component & slits position
3.3 Slits : Length of slits & wallthickness
For fig 9 Shaft Ø D 5 Length of slit l 15
10 30
15 40
20 50
25 60
30 70
For fig 9 Length of slit Wallthickness above upto t 15 1 … 15 30 1.2 30 40 1.4 40 50 1.6 50 60 1.8 60 80 2 80 100 2.5 100 120 3 120 150 3.5 150 4 … 35 80
40 50 60 70 80 90 90 100 110 120 130 135
100 140
120 145
150 150
Design Guideline For Collets
Fig 10
Collets upto Ø 40 free bore in which the material is fed from behind without feeding bar (Turret)
Fig 11
collets in which the material is fed from front
Fig 12
Collets with free bore Ø > 40 in which the material is fed from behind without feedrod as well as automatics collets
Fig 13
Collets on lathe with collet head
Design Guideline For Collets PAGE 4 3.3
SLITS (FORM)
*
Collets up to Ø 20 mm get only slits (fig 10)
*
Collets above Ø 20 mm get slits with slots ( fig 11) shaft Ø above upto 20 40 40 60 60 80 80 110 110 ….
b 5 6 8 10 12
*
Collets in which the length is small in relation to the collet Ø get a longitudinal & crosswise slit
4
Collet Expansion Values ( For collet expansion process see 11.0 page 8 )
shaft Ød above upto … collet expansion 0.5 +0.3
above 12
upto 12 1 +0.5
above 40
upto 40
1.5 +0.5
80
above upto above upto 80 120 120 … 2 +0.5
3 +0.5
Design Guideline For Collets PAGE 5 5 Free Bore Details :
For fig 13 14 15 Free Bore above upto … 5.5 5.5 7.5 7.5 9.5 9.5 14.75 14.75 24 24 32 32 40 40 60 60 80 80 120 120 150
a
R 1.5 2 3 4 5 8 10 15 20 20 20
10 10 12 14 16 20 20 25 25 30 35
For fig 16 Shaft Ø Clamping Ø upto 30 20 40 30 50 40 60 50 75 63 90 78 110 100 130 120
K
R 19 19 19 24 24 24 24 24
5 5 10 10 10 10 10 10
Design Guideline For Collets PAGE 6 6 Longitudinal Grooves :
In collets for profile bars, longitudinal slots as per fig.11 should be provided A/F Hex oct
above up to above up to above up to above up to above up to 5 5 10 10 20 20 40 40 …. … 0.6*0.4 1*0.8 1.2*0.8 1.8*1 2*1.2 1.6*0.8 2*1.0
7 Gripping Bore: for collets used on multispindle longitudinal & transverse grooves are provided. Form of grooves as per fig 12 Transverse grooves for profile bars as per fig 13 longitudinal grooves for round clamping bars Ø as per fig 14
A/F
above up to above up to above up to 20 30 30 40 40 … A/F+1.2 A/F+1.8 A/F+2.5
clampi ng Ø above up to above up to above up to 10 25 25 36 36 … No of groove s 3 6 9 x
60°
40°
80°
Design Guideline For Collets PAGE 7
8 TYPE OF COLLET
1 Push type * Single cone * Double cone
fig 17 fig 18
2 Pull type
fig 19
3 Internal expanding
fig 20
Design Guideline For Collets PAGE 8 9 Material:
Collets are made out of following materials C=0.55 - 0.68, Mn=0.74 - 1.26, Si= 0.76 - 1.04 1 2 3 4
En 45A DIN 1.2826 IS:3749 ~ T55 Si 7 BOHLER SP CS (C=0.6, Si=0.9,Mn=0.4, Cr=1.2, V= 0.1 )
10 HEAT TREATMENT : 1 Clamping portion to HRc 54….56 2 Stock portion tempered to blue ,red yellow resp. from guide Ø D to clamping area 3 Collet Expansion is done as a last operation (i.e. after finish bore grinding & slitting off the small portion near bore ) the collet is heated by flame near the slit ends gradually & universally by rotating on a cone with diameter markings. After heating the collet is pressed from top till the front diameter is expanded uniformly to a desired value. The collet is cooled down on the fixture to room temperature
Smaller collet are uniformly hardened & tempered to HRc 42…45 throughout the length No selective or gradual hardening is carried out.
Design Guideline For Collets PAGE 9 12 Special Manufacturing Instructions :
12.1 No turning lines ,deep tool marks, serrations etc are to be permitted on collets. All sharp edges to be rounded off smoothly. 12.2 Radial runout of the clamping bore to be measured w.r.t. stock dia (Guide dia. )before opening off the slits completely 12.3 No. of slits & division should be made equispaced within ±5" to ensure maintaining T.R. within close specification & collet T.R. accuracy 12.4 collet are provided with hard rubber , polyurethane material stoppers to prevent loose chips , coolant etc entry thro the slits inside the collets fig 16
small or thin walled collets may be co tempered instead of hardened in oil , at a temperature about 250 °c.The additional tempering of the clamping end ,to spring hardness is best effected by cutting it stand on glowing plate or submerging it in a lead bath . For Bohler SPCS the correct tempering temperature is 480°c to 500°c 12.5 Typical Manufacturing & heat treatment of collet * *
Finishing with grinding allowance on the fitting parts, including boring , finish threading or tapping mill the slots, leaving a narrow thward at each slot near chucking part so that the distortion during hardening is largely avoided
Design Guideline For Collets PAGE 10 Fig 23
* * *
*
* *
Harden at temp. mentioned above quenching in oil or austempering Temper the whole collet at 220°c to 240°c Temper the chuckend only. At the process described above the heat falls off gradually on one end to the other the tempering temperature may be guessed from tempering color therefore the surface should be rubbed bright with emery & care should be taken that heating is uniform around the circumference when tempering has progressed for enough (about halfway down the chuck lips ) cool the whole collet rapidly in quench oil Finish Grinding ( stock or locating diameter & taper w.r.t. collet axis by clamping the collet between centers made on pre-bore & free-bore ends in slot stage ) Then taking reference of locating diameter grind the bar clamping bore which is usually the max limit of the component to be clamped in the collet Finally the parts of thwards left tending between the slots & remove burr from slot ends Expand the collet (see procedure on collet expansion )
Design Guideline For Collets PAG 13 Calculating the Clamping force in collet :
Action of clamping forces in collet Clamping forces W developed by the collet is determined as follow : Force Q produced by a drive ( a pneumatic cylinder or manually ) acts upon a collet along it 0-0 . Suppose the collet is having n number of jaws; each jaw will receive a part of force Q= &will act like a wedge mechanism. Each force Q/n produces reaction force Q'/n The conical surface E-H takes up re force R/n where R is the resultant force in the force triangle ABC.The part W'/n is found fro force triangle ABC W'/n = Q'/ntan x hence
W'=Q'/tan x
since W'=W & Q'=Q W=Q/tan x kgf ( N )
E 11
axis Q'/n ction the
Design Guideline For Collets PAG In operation , the collet is subject to friction on its taper surface E-H & on its whole surface In addition, a force needed to flex the jaws & a force nee should be taken into account Then W= Q{1/ tan (x + Q1)+tan Q2} - (T+F) with a collet chuck without the workpiece stop W= Q{1/ tan (x + Q1)} - (T+F) where
Q1=angle of friction on chuck & collet surfaces Q2= angle of friction on collet hole & workpiece surface T=force of flexing collet jaws F=force of compressing return springs
Force T can be assumed collet Ø above up to … 30 50
30 50 80
T kgf 5…10 10…25 25…50
Force F is found from spring diagram The angle of friction Q1 & Q2 are taken 5°43' each.
E 12
