Collet chuck for splined workpieces

A chuck for splined workpieces includes at least two collets, the resilient fingers of which are circumferentially interdigitally related. The work-engaging surfaces of circumferentially adjacent fingers of the chuck are spaced apart a distance at least slightly greater than the circumferential extent of each radially facing splined surface on the workpiece, the arrangement being such that, when a splined workpiece is telescopically engaged with the collets, fingers of not more than one of the collets register with the radial surfaces of the splines so that the remaining collet fingers will grip the base diameter surface of the workpiece when the collets are actuated.

This invention relates to a collet chuck and, more particularly, to a 
collet chuck designed for gripping internally or externally splined 
workpieces. 
Many splined workpieces are, by necessity, gripped in collet chucks when 
machining operations are performed on them. A splined workpiece as used 
herein designates a workpiece having an annular surface from which a 
plurality of regularly circumferentially spaced narrow ribs project 
radially inwardly or radially outwardly. In many instances, especially in 
the case of thin walled splined workpieces, it is preferred to grip the 
workpiece at the base diameter of the workpiece between the splines, 
instead of directly on the radially facing surface of the splines, because 
the base diameter surface usually has a substantially greater 
circumferential extent than the circumferential extent of the radially 
facing splined surfaces. In the case of an externally splined workpiece 
the base diameter is the minor diameter of the workpiece and in the case 
of an internally splined workpiece the base diameter is the major 
diameter. When the workpiece has to be gripped on the base diameter it 
normally has to be circumferentially oriented to a particular position 
relative to the chuck so that the fingers of the collet will engage the 
desired surface on the workpiece when the collet is actuated. However, 
many machines are equipped with automatic workpiece loading devices that 
are not designed to rotate the workpiece to a particular circumferential 
orientation relative to the collet chuck. Thus, such workpiece loading 
devices cannot normally be used for loading splined workpieces on a 
conventional collet chuck. 
The primary object of this invention is to provide a collet chuck on which 
splined workpieces can be loaded with random orientation of the splines 
relative to the fingers of the collet. 
A more specific object of this invention is to provide a chuck which 
includes a plurality of collets which are arranged such that the fingers 
of at most one of the collets will register radially with the radially 
facing splined surfaces on the workpiece when the workpiece is 
telescopically engaged with the chuck regardless of the particular 
circumferential orientation of the splines on the workpiece relative to 
the collet fingers. 
More specifically, the invention contemplates a chuck having a plurality of 
collets, each collet having a plurality of regularly circumferentially 
spaced fingers thereon. The circumferentially adjacent fingers of the 
collets are interdigitally disposed around a common circle. The adjacent 
fingers are spaced apart at their work-gripping surfaces a distance at 
least slightly greater than the circumferential extent of the radially 
facing surface of a spline on the workpiece so that, when the workpiece is 
telescopically engaged with the chuck, fingers of only one of the collets 
can at most be radially aligned with the radially facing spline surfaces 
on the workpiece. Both collets are actuated after the chuck is loaded with 
a workpiece. However, if the fingers of one of the collets engage the 
radially facing spline surfaces on the workpiece, then said one collet is 
released so that the only collet or collets which remain operative to grip 
the workpiece are those collets all the fingers of which register radially 
with the base diameter surface of the workpiece.

The chuck shown in FIG. 1 comprises a main body portion, generally 
designated 10, which includes an adaptor 12 adapted to be mounted on the 
spindle 14 of a machine tool by means of screws 16. A collet expander 18 
and a spacer ring 20 are secured to adaptor 12 by screws 22. Additional 
screws 24 are employed for securing spacer ring 20 to expander 18. The 
front end of the chuck body 10 comprises an annular part stop 26 secured 
to spacer ring 20 by screws 28. 
The collet expander 18 has an outer circumferentially continuous flange 30 
and a reduced diameter, forwardly extending nose 32. The chuck illustrated 
is one for engaging an internally splined workpiece 33. Thus, the nose 32 
is formed with a conical portion 34 at its forward end and a cylindrical 
portion 36 axially adjacent the outer flange 30. Within the chuck body 
between the nose 32 and the spacer ring 20 there are arranged two collets, 
generally designated 38 and 40. Collet 38 has at its rear end an outer 
peripheral flange 42, the inner periphery of which has a close sliding fit 
with the cylindrical portion 36 of nose 32. The outer periphery of flange 
42 has a close sliding fit with the inner periphery of spacer ring 20. A 
plurality of radially resilient collet fingers 44 extend forwardly from 
and are integrally connected with flange 42 as at 46. The inner periphery 
of the forward ends of fingers 44 are conically tapered to interfit with 
the conical surface 34 of nose 32. The radially outer surfaces of the 
forward ends of fingers 44 form cylindrically shaped work-gripping 
surfaces 48. 
Referring to FIG. 2 it will be observed that the workpiece 33 has four 
equally spaced, radially inwardly projecting splines 50. In FIG. 1 the 
radially inwardly facing surfaces of splines 50 are designated 52 and the 
major diameter surface of the workpiece is designated 108. From FIG. 2 it 
will be noted that at each side of the work-gripping surface 48 the front 
end portion of finger 44 is notched, as at 56. 
Referring again to FIG. 1, the flange 42 of collet 38 is rigidly secured to 
a plurality of pins 60 by screws 62. Pins 60 extend rearwardly through 
openings 64 in the flange 30 of expander 18 and are brazed or otherwise 
rigidly secured within openings 65 in radially extending arms 66 of a 
collet puller 68. As shown in FIG. 4, collet puller 68 is of generally 
cruciform shape and has a rearwardly extending central hub 70 provided 
with a threaded bore 71 for connection with a tubular drawbar 72 
associated with spindle 14 of the machine tool. 
The other collet 40 has generally the same configuration as the collet 38 
described. Collet 40 has a rear flange 74, a plurality of 
circumferentially spaced fingers 76, the forward ends of which are 
internally tapered to interfit with conical surface 34 of the nose 32, and 
the external surface of which is formed with work-gripping surfaces 78 
which, as shown in FIG. 2, are defined by notches 80 at each side of the 
finger. In the arrangement illustrated each collet has eight work-gripping 
fingers. The outer diameter of the workgripping surfaces 78 on fingers 76 
is the same as the outer diameter of the work-gripping surfaces 48 on 
fingers 44. It will also be observed from FIG. 2 that the spaces 82 
between the adjacent work-gripping surfaces 48,78 have a circumferential 
extent greater than the circumferential extent of the surfaces 52 of 
splines 50. This is an important feature of the present invention. 
Referring again to FIG. 1, the flange 74 of collet 40 is connected to pins 
84 by screws 86. Pins 84 also extend through openings 88 in the flange 30 
of expander 18 and are rigidly secured in openings 89 in a second collet 
puller 90. Collet puller 90 is connected to a second drawbar 92 by means 
of a screw 94. Drawbar 92 is arranged concentrically within drawbar 72. It 
will be observed that flange 42 of collet 38 is located rearwardly of 
flange 74 of collet 40. Thus, flange 74 is provided with a plurality of 
circumferentially spaced notches 96 (FIG. 1) around its inner periphery to 
accommodate the fingers 44 of collet 38 and flange 42 is provided with a 
plurality of openings to slidably accommodate puller pins 84. It will also 
be observed that collet puller 68 is located rearwardly of collet puller 
90. The rear face of collet puller 90 is provided with a recess 92 to 
receive puller 68 in nested relation. Around its outer periphery puller 90 
is provided with four equally spaced notches 98 to accommodate the puller 
pins 60 for collet 38. 
The two drawbars 72,92 can be operated by any suitable means. In the 
arrangement illustrated a hydraulic cylinder 100 is employed to 
reciprocate drawbar 72 and a similar hydraulic cylinder 102 is employed to 
reciprocate drawbar 92. Any suitable means may be employed for detecting 
the extent of retraction of the two drawbars. In the arrangement 
illustrated these means are illustrated as microswitches 104,106. The 
microswitches are actuated by shoulders 107 on the drawbars when the 
associated drawbar is fully retracted, thus indicating that the workpiece 
has been properly gripped by the collet fingers. When either of the 
cylinders 100,102 are actuated and the associated microswitch is not 
tripped, this is an indication that the associated drawbar has not been 
fully retracted and the corresponding cylinder will accordingly move 
forward to its starting position and thus collapse the fingers of the 
associated collet. 
In operation, a workpiece 33 with the radially inwardly projecting splines 
50 is telescopically arranged over the ends of the two sets of collet 
fingers 44,76 with the splines 50 randomly oriented relative to the 
fingers of the two collets. Since, as pointed out previously, the spaces 
82 between the adjacent work-engaging surfaces 48,78 of the two sets of 
collet fingers has a greater circumferential extent than the radially 
facing surfaces 52 of splines 50, it follows that the work-engaging 
surfaces of several fingers of at most one of the collets will register 
radially with splines 50. In the arrangement shown in FIG. 2 the 
work-engaging faces 48 of four fingers 44 spaced 90.degree. apart register 
radially with the splines 50. The work-engaging faces of the remaining 
fingers of both sets register radially with the major diameter surface 108 
of the workpiece which extends circumferentially between the successive 
splines 50. Therefore, when the two cylinders 100,102 are actuated to 
retract the drawbars 72,92 collet 40 will be fully retracted. Microswitch 
106 will be tripped so that the work-engaging surfaces 78 of its fingers 
76 will remain in gripping engagement with the workpiece at the major 
diameter surface 108 thereof. However, upon retraction of collet 38 the 
work-engaging surfaces 48 of four of its fingers will immediately contact 
the spline faces 52 and prevent further retraction of collet 38. Thus, the 
microswitch 104 associated with drawbar 72 will not be tripped within the 
required time interval so that the piston of cylinder 104 will be advanced 
and thus release the fingers of collet 38. The two collets will therefore 
assume the condition shown in FIG. 1. 
In the arrangement illustrated, since the workpiece 33 has four equally 
spaced splines 50, two collets, each provided with eight circumferentially 
spaced fingers, will ensure that only four of the fingers of only one of 
the collets will at most register radially with the spline faces 52. If, 
by chance, the workpiece were telescoped over the collet fingers with the 
splines 50 registering fully with the spaces 82 between adjacent collet 
fingers, the workpiece would then be gripped at its base diameter surface 
by all of the fingers of both collets. If the workpiece had six splines, 
then two collets, each provided with three or six fingers would be 
employed. Likewise, if the workpiece had three or nine equally spaced 
splines instead of two, then the chuck would employ three collets instead 
of two. In any event, the spacing between the work-engaging surfaces of 
adjacent fingers must at all times have a greater circumferential extent 
than the radially facing spline surfaces and the number of collets 
employed in the chuck will depend upon the number of splines on the 
workpiece.