Chuck assembly and collet

The chuck assembly and the collet for retaining an end mill tool against axial pullout. The collet includes a radially compressible body having a tapered outer surface, a central bore and a drilled radial aperture extending from the outer surface into the central bore. The radial aperture has an undercut or larger diameter medial portion with a movable pin mounted therein, said pin being movably mounted and, adapted to extend into the bore to retain the tool. The pin has a hole drilled through with a spring bar mounted therein. The ends of the spring bar are compressed to a length smaller than the diameter of the radial aperture and inserted into the larger undercut portions where the expansion of the spring bar retains the pin. The hole in the pin is larger than the diameter of the spring bar to allow the pin to move along its axis (radially into the collet bar). The pin has a lower chamfered end which is urged inwardly into the bore as the collet is tightened in the chuck assembly with the chamfered end engaging a rear bevel end on a flat surface on the tool to secure the tool within the collet, and whereby the pin can move outwardly to release the tool when the collet is removed from the chuck assembly.

CROSS REFERENCE TO RELATED PATENTS 
The present invention is related to and an improvement upon the invention 
disclosed in U.S. Pat. No. 4,197,044 concurrently filed by Willard 
Cummings entitled "Chuck Assembly and Collet" and assigned to the assignee 
of the present application. This patent application, which is specifically 
incorporated herein by reference, is referenced to as the "Non-Pullout 
Collet Patent". 
The present invention is also related to a patent application Ser. No. 
2,116 concurrently filed by Better and Lehde entitled "Slotted Collet and 
Method of Making" and assigned to the assignee of the present application. 
This patent application, which is also specifically incorporated herein by 
reference, is referred to as the "Slotted Collet Patent". 
FIELD OF THE INVENTION 
The present invention relates generally to a holding apparatus for cutting 
tools. More particularly, the present invention relates to a collet and 
chuck assembly for holding an end mill (or similar) tool to prevent axial 
or rotational movement with respect to the apparatus during machining. 
An end mill tool is a cylindrical cutting tool which has a cutting (or 
milling) edges around the round portion at one or more of its ends along 
with cutting teeth on its end toward at least one of its forward ends. The 
tool has a generally cylindrical rear or central shank with at least one 
beveled-ended flat surface which is secured in the collet and chuck 
assembly during machining. 
BACKGROUND ART 
Various designs have been suggested for providing a collet and chuck 
assembly for securing an end mill tool therein against axial movement of 
the tool out of the assembly and against rotation of the tool with respect 
to the assembly and collet. 
Such designs generally include an aperture through the collet, with a 
movable pin mounted therein for engaging a flat surface on the end mill 
shank. Mounting and retaining the pin suitably has been a problem in the 
prior art collets, except for the Non-Pullout Collet Patent discussed 
later. The pin should be easily movable to secure and release the tool, 
while resisting accidental separation of the pin from the collet. However, 
for service or repair, the pin should be quickly and easily released. 
Further, the mounting and retaining mechanism should not be on the 
external surface of the collet, to minimize the chance of damage thereto. 
Cutting tools for chuck assemblies may range from only slightly smaller 
than the bore in the chuck to substantially smaller, with the thickness of 
the collet wall varying accordingly. An ideal collet for an end mill is 
not dependent on a particular wall thickness. More particularly, a very 
thin-walled collet (i.e., where the tool shank is almost as the chuck 
bore), must suitably accommodate the pin and its retention system, while 
allowing limited pin movement. 
One approach suggested in the prior art was to provide the outer collet 
body and pin with a groove, in which an external spring retaining ring is 
mounted. 
Another prior art approach was to drill a hole through the collet body 
perpendicular to and intersecting the pin aperture. The movable pin is 
provided with a hole also, and a roll pin is inserted into the aligned pin 
hole and collet body hole to retain the movable pin. 
Typically, such designs have at least one of the following disadvantages: 
expensive to manufacture; time-consuming, difficult and/or expensive to 
assemble; parts, other than the collet body and the pin itself, which are 
on the external surface of the collet and subject to wear and destruction. 
Examples of such collets are shown in U.S. Pat. Nos. 3,195,909; 3,425,705; 
3,618,962; and others. 
The collet design in the referenced Non-Pullout Collet Patent overcomes 
many of the disadvantages and limitations of the prior art. However, for 
thin-walled collets, the design in the Non-Pullout Collet Patent does not 
suffice. The pin and collet walls are simply shrunk to a thickness which 
does not allow an undercut and stepped radial aperture, respectively to 
allow a radially-movably mounted pin. 
It is thus apparent that there are disadvantages and limitations of the 
prior art collets for retaining an end mill tool. Lacking is a collet 
which is reliable and economical to manufacture, while quickly engaging 
and disengaging an end mill-type tool without external parts to be 
damaged. Other disadvantages and limitations of the prior art collets and 
chuck assemblies will be apparent from the following description of the 
present invention. 
SUMMARY OF THE INVENTION 
The present invention is a chuck assembly and collet which overcomes the 
limitations and disadvantages of the prior art collets previously 
described. 
The present invention is a chuck assembly and collet which provides a 
convenient means for securing an end mill or similar tool when desired and 
for quickly and easily releasing it. The collet is relatively inexpensive 
to manufacture and assemble, easily and quickly assembled and has a 
minimum of external parts. The collet also has a high reliability and 
resistance to damage and to accidental separation of parts which could 
lead to a loss of parts. Further, the collet and chuck assembly of the 
present invention are equally useful in both thin and thick wall collets. 
The chuck assembly includes a collet having a pin mounted in a radial 
aperture with an undercut extending therethrough with a spring bar mounted 
in the undercut. The spring bar, which has a free or no-force diameter 
slightly larger than the aperture portion and less than the medial 
undercut is inserted through the pin in the pin aperture, then the pin and 
spring bar assembly are inserted into the collet aperture with the spring 
bar in the undercut. The spring bar is compressed for insertion, then 
expands to retain the pin within the collet aperture. A pin aperture 
larger than the diameter of the spring bar allows the pin to move along 
its axis (radially with respect to the collet) to lock the tool shank 
therein. 
The assembly of the present invention appears to be less expensive to 
manufacture than the design of the Non-Pullout Collet Patent. 
The foregoing and other objects and advantages of the present invention 
will become apparent to one skilled in the art in view of the following 
description and claims and the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 shows a cross-sectional view of a part of a chuck assembly 10 of the 
present invention. The chuck assembly 10 includes a chuck body or collet 
holder 100 and a lock nut 200. A collet 300 is mounted within the collet 
holder 100 and has an end mill tool 400 mounted therein. The chuck 
assembly 10 and its components are the same as described in the referenced 
Non-Pullout Collet Patent except for a pin and aperture structure, which 
patent should be consulted for greater detail. 
The collet holder 100 is of a well-known and conventional design and 
includes a body 110 with external forward screw threads 120 and an 
internal, inwardly tapering bore 130 extending rearwardly from the forward 
end of the body. A rear portion 140 is a shank which is configured to be 
secured in a machine tool or spindle. 
The lock nut 200 is also a conventional design. The lock nut 200 includes a 
body 210 with internal threads 220 adapted to mate with the external 
threads 120 on the collet holder 100. A second member 230 of the lock nut 
200 is coupled to the body 210 with ball bearings 240 and the member 230 
has a projection 232, the purpose of which will be explained later. 
The collet 300 is preferably made of an appropriate spring-type steel which 
has been hardened and drawn, as is well-known and customary in making 
collets. The collet has a body with an internal tool-receiving bore and 
with an outside external surface which tapers generally to a smaller rear 
diameter. 
The external surface of collet 300 has a forward portion 310 and a tapering 
rear portion 330, separated by an annular groove 320. The rear portion 330 
seats against and engages internal walls of the tapered holder bore 130 
when the collet 300 is fully inserted. Preferably, two (or more) 
spatially-separated surfaces of the rear collet portion 330 are in contact 
with the bore 130 providing good engagement within the collet holder 100. 
The lock nut projection 232 cooperates with the forward collet portion 310 
and annular groove 320 to release the collet 300 from the collet holder 
bore 130 as the lock nut 200 is unscrewed in disassembly. 
A radial aperture 370 (preferably drilled through the collet 300) extends 
through the collet 300 medially along the length of the collet. The 
aperture includes a first portion 372 and an undercut diameter 374 
portion. A tool-securing pin 380 is positioned within the aperture 370 and 
is held in place by a spring bar 390. 
The pin 380 has structure which is described in detail in connection with 
FIGS. 3 and 4. The pin 380 is radially movable through a limited range of 
radial movement when assembled, as also will be discussed later. 
The spring bar 390 is shown in FIGS. 3 and 5 and will be discussed in 
greater detail in connection with those figures. 
The tool 400 is a conventional tool (such as an end mill) which has forward 
cutting surfaces 410 and rear shank 420. The forward cutting surfaces 410 
have side surfaces, as well as end surfaces, for cutting and may have a 
tendency for axial pullover. Therefore, the shank 420 of an end mill tool 
has one or more flat surfaces with forward and rear beveled ends 432, 434 
for tool retention. The beveled ends 432, 434 have a 45.degree. angle with 
respect to the axis of the tool. The beveled flat surface, when suitably 
engaged within the collet, prevents the tool from being pulled out of the 
holder. 
FIG. 2 is a cross sectional view of the chuck assembly 10, showing the 
chuck body 110, the lock nut 200, the collet 300 and the tool 400. The 
collet 300 include slots 305 of the type described in the referenced 
Slotted Collet Patent to provide radial compressibility and resiliency 
alternatively, other slotting methods of providing radial compression and 
resiliency are known and could be used. The tool 400 has the flat surface 
430 shown in this view slightly above the bottom of the tool locking pin 
380. The spring bar 390 is shown in a side, cross sectional view. 
FIG. 3 is an enlarged view of the pin 380, spring bar 390, aperture 370 and 
tool 400 prior to assembly of the pin into the aperture 370. 
The pin 380 is generally cylindrically and includes a radiused or rounded 
head 382. A drilled radial hole or aperture 384 extends through the pin 
below the head 382. The pin 380 has a lower chamfered portion 387 which 
has a 45.degree. angle for engaging the 45.degree. beveled surface 432 of 
the tool 400. 
The spring bar 390 has ends 392, 394. The spring bar 390 is mounted within 
the hole 384 of the pin. The ends 392, 394 extend beyond the pin 380 
normally, but may be compressed to a size no larger than the pin diameter. 
The ends 392, 394 are compressibly mounted to the spring bar 390 as 
discussed in FIG. 5. The hole 384 in the pin is larger than the diameter 
of the spring bar 390 to allow the pin 380 to move radially with respect 
to the collet 300 (up and down in FIG. 3) without movement of the spring 
bar 390. This movement allows the pin 380 to lock and release, as desired, 
the tool 400. 
The aperture 370 has a chamfered entry 371, a portion 372 of generally 
uniform diameter and an undercut portion 374. The undercut portion 374 
receives the ends 392, 394 of the spring bar 390 when the pin is inserted 
in the aperture 370. 
FIG. 4 shows a cross sectional portion of the collet 300. The portion 372 
of the aperture is shown, as is the undercut portions 374. The undercut 
portions 374 may be formed without requiring a separate setup of the 
collet 300 by using a Woodruff cutter and moving the collet 300 slightly 
back and forth when the Woodruff cutter is in place. Dotted lines 601, 602 
show the extremes of the movement of the cutter to form the undercut 374. 
Of course, other suitable methods of making the undercut could be employed 
to advantage. 
FIG. 5 shows a cross sectional view of the spring bar 390 taken along the 
line V--V in FIG. 3. The spring bar 390 is preferably of the type used to 
mount a watch band to a watch and is available commercially from Polly 
Trading Co. (N.Y., N.Y.) Quick Fit or Regal. The spring bar 390 includes 
the ends 392, 394. The ends 392, 394 have enlarged portions 392a, 394a, 
respectively, which are held within a body 396. Ends 396a of the body are 
crimped over (or have other suitable retaining) to hold the ends 392, 394 
in. A spring 398 urges the ends outward normally. The ends 392, 394 may be 
compressed or urged inwardly by compressing the spring 398. 
The foregoing description of the preferred embodiment is merely exemplary 
of the present invention. The structure shown may be modified in one of 
several ways known to those skilled in the art, and further, some features 
of the present invention may be used without the corresponding use of 
other features. For example, other configurations of spring bars or spring 
members could be substituted, either with or without changes to the 
structure of the aperture of the pin. The collet aperture could be made in 
one of the several diverse manners. The pin might be of uniform size on 
its ends and need not be round. Accordingly, the present description is 
illustrative of the present invention only and should not be taken as 
limiting the scope of the invention which is solely by the following 
claims.