Chuck jaw and mounting therefor

A top jaw adapted for mounting on and attachment to the master jaw of a conventional work holding chuck and simultaneously during attachment thereof to be located radially against a fixed stop by a double T-nut of unique configuration, the latter being movable by an actuator screw in T-slots provided in the jaws, one portion of the T-nut and the complementary T-slot in the top jaw in which it is mounted being inclined with respect to and sloping toward the interface between the top and master jaws so that tightening of the T-nut by the actuator screw forces the top jaw radially against the stop and simultaneously axially against the mating surface of the master jaw, the taper angle of T-nut and the lead angle of the screw threads mutually cooperating to lock the top jaw on the master jaw in use.

BACKGROUND OF THE INVENTION 
In work holding chucks of the type having replaceable top jaws mounted on 
and detachably fastened to master jaws, it is conventional to fasten the 
top jaws by hold-down screws that may extend through holes in the top jaws 
and into T-nuts disposed in radial T-slots provided in the master jaws, or 
alternatively, by hold-down screws that typically spread split dovetail 
members in dovetail slots. In the case of the dovetail arrangement, the 
fact that the hold-down screws extend through holes in the top jaws 
reduces to that extent at least the area of frictional engagement between 
the dovetail members and the slots. Also, in both of these constructions, 
the T-slots or dovetail slots as the case may be extend radially of the 
master jaws so that, when the hold-down screws are loosened, the top jaws 
can be adjusted radially in accordance with the size of workpiece to be 
held thereby. 
Precise radial positioning of the top jaws conventionally is achieved by 
set screws at one end or the other of the jaws. In these chucks, the top 
jaws are held primarily, if not entirely, by friction between the T-nuts 
or dovetail members and the slots. Consequently, any loosening of the 
hold-down screws in use due to vibration or otherwise results in a 
lessening of clamping pressure that may cause the work to fly out of the 
chuck and result in possible injury to persons and damage to equipment in 
the vicinity of the chuck. 
Top jaws mounted and secured in the manner described above are replaceable 
so that the chuck can be adapted for different kinds and forms of 
workpieces. However, the jaw change operation is tedious and time 
consuming since it requires that all of the hold down screws be removed 
and then replaced. Since the screws and other parts of the jaw assemblies 
are completely disassembled they are liable to be misplaced or even lost 
during the changeover operation. Further, while the adjustable stops 
permit limited radial adjustment of the top jaws for different diameter 
workpieces, the adjustment is time consuming since the chuck has to be 
tested for runout after each adjustment. 
Thus, there is a need in the art for a top jaw mounting that holds the top 
jaws securely in use but that also permits them to be easily and quickly 
removed and replaced. 
SUMMARY OF THE INVENTION 
The present invention provides a novel form of top jaw mounting that 
utilizes a double T-nut having T-portions disposed in confronting T-slots 
in the top and master jaws. The master jaw T-slot and the T-portion of the 
T-nut disposed therein extend at right angles to the chuck axis. However, 
the top jaw T-slot and its T-portion are inclined with respect to the 
chuck axis disposed and in converging relation with respect to the 
interface between the two jaws. An axially stationary but rotatable screw 
in the master jaw extends through the T-nut; and, when this screw is 
tightened, it draws the inclined T-portion of the T-nut solidly against 
the inclined T-slot to urge the top jaw radially against a fixed stop and 
simultaneously to force the top jaw solidly in an axial direction against 
the master jaw. Ideally, the angle of inclination of the T-portion and 
T-slot last referred to is substantially the locking angle of the material 
from which the jaw is made so that the inclined T-portion mutually 
cooperates with the helix angle of the actuator screw to hold the top jaw 
securely in use. 
Sufficient clearance is provided above the inclined T-portion so that, when 
the actuator screw is loosened, the top jaw can be tilted to disengage the 
radial stop so that the top jaw can be pulled off of the T-nut and removed 
from the master jaw. This can be accomplished in many instances by a 
single turn of the hold-down screw. Under these circumstances, the jaw can 
be removed and replaced in as little as 60 seconds. There are no parts 
that can be easily lost or misplaced. Thus, it is feasible for short 
production runs to have a different set of jaws for each job thus 
eliminating the need to test for position and runout each time the jaws 
are changed. Contrariwise, the top jaws can be mounted on and fixed 
securely to the master jaws by a simple turn or two on the T-nut screw.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawing, wherein for the purpose of illustration is shown a 
preferred embodiment of the invention, the numeral 12 designates the jaw 
assembly of this invention shown in exploded perspective view in FIG. 1. 
More particularly, the jaw assembly 12 comprises a master jaw 14 that is 
mounted on and preferably is formed integrally or in one piece with the 
jaw actuator 16 of a conventional chuck such as the one shown in FIG. 2 
and designated generally by the numeral 18; a top jaw 20 (shown as a jaw 
blank in FIG. 1 and other views of the drawing); a T-nut 22 that interfits 
with T-slots 24 and 26 in the master and top jaws; and an actuator screw 
28 threaded into the T-nut and mounted for turning or rotational movement 
but restrained against axial movement in the master jaw. 
In FIGS. 1-6, the jaw assembly 12 of this invention is shown on and in 
operative association with a work holding chuck of the type known in the 
trade as a Woodworth Universal Ball-Lok chuck. A chuck of this type is 
disclosed in U.S. Pat. No. 3,069,181 which was filed Aug. 3, 1961 in the 
names of George Hohwart and Paul Toth as joint inventors, and was issued 
Dec. 18, 1962 and assigned to the same assignee as this application. Since 
the construction and operation of the patented chuck is disclosed in 
detail in the patent document, it is not necessary for a complete 
description and understanding of the jaw mounting of this invention to 
repeat the description of the chuck in this application; and the 
disclosure of the patent therefore is incorporated by reference herein. 
Suffice it to say that the patented chuck has three jaw actuators 16 in 
the form of rocker arms 30 (only one of which is shown in FIG. 2) arranged 
concentrically about the chuck axis and spaced equidistantly with respect 
to each other. The three rocker arms 30 are identical in construction and 
operation and each is swiveled at 32 intermediate the ends thereof on the 
front cover plate 34 of the chuck body 36. The inner or rearward ends of 
the rocker arms 30 carry slidable swivel mountings 38 and are connected by 
the latter to a jaw actuator 40. In the particular construction here shown 
by way of example, the chuck body 36 is mounted on and rotatably driven by 
the lathe spindle 42; and the jaw actuator 40 is connected by a screw 44 
to a drawbar 46 that extends axially through the spindle. The drawbar, in 
turn, is connected at the rearward end thereof to a power cylinder (not 
shown). 
In operation, reciprocation of the jaw actuator 40 slides the rear swivel 
mountings 38 back and forth on the rocker arms 30. The front swivel 
mountings 32 are spaced equidistantly radially from the rotational axis of 
the chuck as are the rear swivel mountings 38; but the radial spacing of 
the front swivels is different from the radial spacing of the rear swivels 
38. Consequently, sliding movement of the rear swivel mountings 38 on the 
rocker arms 30 by reciprocation of the actuator 40 and the drawbar 46 
causes the rocker arms to pivot in the front swivel mountings 32 and work 
holding jaws 20 on the outer or forward ends of the rocker arms to move 
radially with respect to the chuck axis into and out of clamping 
engagement with a workpiece disposed centrally of the jaws. 
In FIG. 2 of this application and in FIG. 1 of the patent drawing, the rear 
swivel mountings 38 are spaced a lesser distance from the chuck axis than 
the front swivel mountings 32 so that retraction of the actuator 40 rocks 
the jaws 20 radially inwardly into clamping engagement with a workpiece 
disposed centrally on the jaws; and, contrariwise, forward movement of the 
actuator 40 rocks the jaws 20 radially outwardly to release the workpiece. 
Thus, the rocker arm arrangement shown in FIG. 2 of this application 
adapts the chuck for external clamping. On the other hand, if the rear 
swivel mountings 38 are spaced a greater distance from the chuck axis than 
the front swivel mountings 32, as shown in FIG. 5 of the '181 patent, 
retraction of the actuator 40 moves the jaws 20 radially outwardly to 
clampingly engage the work and forward movement of the actuator rocks the 
jaws 20 radially inwardly to release the work. Thus, the rocker arm 
arrangement last described adapts the chuck for inernal clamping. In many 
chucks of this type, it is possible to change from internal clamping to 
external clamping, or vice versa, simply by turning the rocker arms 
180.degree. and substituting a different size actuator. 
From the foregoing, it will be readily apparent that, in this form of the 
invention, the jaw assemblies 12 are identically mounted on the rocker 
arms 30 regardless of whether the chuck is adapted for external or 
internal clamping; and it is a feature of the invention that, if the 
rocker arms cannot be simply reversed as suggested above, the chuck can be 
modified for internal clamping to external clamping simply by reversing 
the rocker arms and changing actuators as described above or at most by 
replacing the front plate assembly and the actuator 40, and in either 
event, replacement of the top jaw members 20. Manifestly, however, it is 
necessary most often in the use of the chuck simply to replace the top jaw 
members 20 in order to adapt it to a different diameter workpiece or to a 
different shape or form of workpiece. In this connection, it will be 
appreciated also that, in use in normal operation of the chuck, the jaws 
20 are moved radially only a sufficient distance to clamp and release the 
workpiece and to permit the latter to be loaded and unloaded when the jaws 
are released or open. Thus, in order to adapt the chuck for a different 
diameter or form of workpiece, the top jaws only must be replaced; and 
since the need to do this may occur relatively frequently, it is 
particularly advantageous to be able to make the replacement essentially 
quickly. As suggested, the top jaw mounting 20 embodying the present 
invention achieves this advantage in a novel and effective manner and it 
further permits the changeover to be accomplished in a manner that assures 
secure retention and accurate positioning of the top jaws at each 
replacement. 
As clearly shown in the drawing, the master jaw 14 is formed with a flat 
top surface 48 that seats the top jaw 20; and the latter is formed with a 
flat bottom surface 50 that seats on and solidly engages the top of the 
master jaw. Thus, the top jaw 20 is free to slide longitudinally of the 
master jaw 14 radially of the chuck within limits in its radial outer 
movement defined by an upstanding ledge or stop 52 formed integrally on 
the master jaw at the outer end of the supporting surface 48. The master 
jaw T-slot 24 is conventional in many chucks and is disposed medianly of 
the top surface 48. Both the stem portion 54 and the head portion 56 of 
the T-slot 24 extend longitudinally entirely through the master jaw. Thus, 
in this form of the invention, the T-slot 24 opens through both the inner 
and outer ends of the master jaw including the stop 52 and the head 
portion thereof extends parallel to the top surface 48 and at right angles 
to the rotational axis of the chuck. 
The bottom face 50 of the top jaw 20 is formed with a shallow groove or way 
62 that is disposed medianly thereof and through ends 64 and 66. Also, the 
groove 62 complements and is essentially the same width as the stem 
portion 54 of the master jaw T-slot 24. On the other hand, the inclined 
T-slot 26 extends from the end 64 longitudinally only part way through the 
top jaw 20, as perhaps best shown in FIG. 6; and the head portion 68 of 
the T-slot is inclined angularly radially inwardly and axially rearwardly 
of the top jaw and in converging relation with respect to the bottom 
mounting surface 50 thereof. The stem portion 70 of the T-slot 26 
preferably is the same width as the bottom groove 62. 
The double T-nut 22 has bottom and top head portions 72 and 74 that 
interfit with the head portions 56 and 68 of the T-slots 24 and 26, 
respectively; and the two head portions 72 and 74 are joined by an 
interconnecting neck portion 76. As perhaps best shown in FIG. 1, the top 
head portion 74 is substantially shorter than the bottom head portion 72; 
and it extends from one end of the T-nut 22 about half the length thereof. 
A guide member 58 of the same width as the neck portion 76 is disposed at 
the end of the T-nut remote from the head portion 74. Both the neck 
portion 76 and the guide member 58 fit snugly but slidably in the stem 
portions 54 and 70 of the T-slots so as to locate and guide the top jaw 
centrally on the rocker arm 16 and on the seating face 48 of the master 
jaw 14. To this end, the top T-nut head portion 74 has the same angle of 
inclination with respect to the bottom head portion 72 that the head 
portion 68 of the top jaw T-slot has with respect to the head portion of 
the master jaw T-slot 24. Thus, when the double T-nut 22 is moved radially 
outwardly with respect to the master and top jaws 14 and 20, the 
undersurfaces of the two head portions 72 and 74 define oppositely facing 
pressure surfaces that seat or tighten against confronting shoulders 
defined by the head portions of the T-slots 22 and 24 in which they travel 
and the wedging action resulting from the inclined orientation of the two 
head portions 68 and 74 xerts a component of force that slides the top jaw 
20 radially outwardly against the stop 52 and simultaneously draws the top 
jaw axially rearwardly solidly against the supporting top surface 48 of 
the master jaw. As suggested, movement of the top jaw 20 back and forth on 
the master jaw 14 is confined and guided by the neck portion 76 of the 
T-nut and the guide member 58. 
As indicated previously, movement of the double T-nut 22 is accomplished 
according to the present invention by the actuator screw 28 that extends 
longitudinally through and is in threaded engagement with an internally 
threaded hole 78 in the T-nut. A radial flange or collar 80 formed on the 
actuator screw 28 adjacent one end thereof is received in a transverse 
slot 82 formed in the master jaw 14 at opposite sides of the T-slot stem 
portion 54 immediately inwardly of the stop 52. Thus, the screw 28 is free 
to turn or rotate relative to the master jaw 14; but it is captured or 
confined against longitudinal movement so that rotation of the screw in 
one direction or the other causes the T-nut to move either inwardly or 
outwardly in the T-slots 24 and 26. When the actuator screw 28 is rotated 
in a direction to move the T-nut 22 in the T-slots radially outwardly with 
respect to the chuck axis, it also acts initially to move the top jaw 20 
radially outwardly on the master jaw 14 and against the stop 52. When this 
occurs, continued turning of the actuator screw 28 simply tightens the 
head portions of the T-nut against the T-slots 24 and 26 and presses the 
top jaw 20 simultaneously radially outwardly against the stop 52 and 
axially rearwardly against the master jaw 14. Thus, the stop 52 positions 
the top jaw 20 radially on the master jaw 14 and also holds it securely in 
its located position when the jaws are moved into clamping engagement with 
a workpiece in the chuck. To assure secure retention of the top jaw 20 on 
the master jaw 14, the angle of inclination of the T-nut head portion 74 
and the head portion of the T-slot 26 in which it travels preferably is 
disposed at or substantially at the locking angle of the metal from which 
the parts are made. In the case of tool steel normally used in the 
manufacture of these parts, the locking angle is substantially 
16.degree.-18.degree.. 
The actuator screw 28 preferably extends away from the threaded section 
thereof beyond the radial flange 80 and the projecting portion is formed 
with angularly related, hexagonal peripheral faces 84 that permits the 
screw to be readily turned by a conventional wrench such as a socket 
wrench or the like. The opposite end of the actuator screw 28 extends 
beyond the threaded portion of the shank and the extremity thereof is 
formed also with angularly related hexagonal faces 86 that serve the same 
purpose as the faces 84 at the other end of the screw. In this connection, 
it will be observed that the actuator screw 28 is of sufficient length so 
that one end thereof is disposed adjacent the radially outer end of the 
master jaw 14 and the other end thereof is disposed inwardly of the master 
jaw. As a result of this particular construction and arrangement of parts, 
both ends of the actuator screw 28 are readily accessible for actuation by 
a wrench regardless of whether the chuck is in the external chucking mode 
shown in FIG. 2 or the internal chucking mode shown in FIG. 6. 
The top jaws 20 normally are made initially as a solid block or jaw blank, 
as shown in FIG. 2 for example, and the jaw blank is recessed as at 88 
(FIG. 4) to accommodate the particular workpiece. In this connection, it 
is contemplated that the recess 88 be adapted to engage the part directly, 
as shown in FIG. 4, or it may be provided according to conventional 
practice with work grips of the type shown in U.S. Pat. No. 3,459,433, for 
example. 
After the jaw blank has been cut away or recessed to accommodate the work, 
the radial or rear face of the jaw that engages the stop 52 may be 
recessed or beveled as shown at 90 to position the clamping surface of the 
jaw precisely with respect to the rotational axis of the chuck. 
In practice, the top jaw 20 can be easily and quickly released for removal 
from the master jaw 14 by a simple rotational movement of the actuator 
screw 28. As soon as the screw is loosened, the inclined top head portion 
74 of the double T-nut 22 moves away from the surface of the T-slot 24 
normally engaged thereby in the normal use of the chuck; and, as the T-nut 
advances in the slot, the clearance normally provided above the head 
portion 74 permits the radially outer end of the jaw to be lifted or 
tilted away from the master jaw sufficiently to clear the stop 52 so that 
the top jaw can be pulled off of the inclined T-nut head. If necessary or 
desirable, the outer bottom corner of the top jaw can be beveled, as shown 
at 90 in FIG. 1, to facilitate disengagement thereof from the stop 52 and 
removed from the master jaw. Manifestly, after the top jaw 20 has been 
removed in the manner described, a substitute jaw can be mounted in its 
place and securely attached to the master jaw by reversing the operations 
required for removal of the jaw. Again, only a simple turn or two of the 
actuator screw 28 is required to attach the substitute top jaw 20 securely 
on the master jaw 14; and, once the actuator screw has been tightened to 
secure the substitute top jaw, the latter will be held precisely in the 
desired location position on the master jaw until the actuator screw is 
again loosened. 
While the top jaw mounting of this invention is primarily adapted and 
pre-eminently suited for use on the Woodworth Universal Ball-Lok chuck, as 
described above, it is readily adaptable also to other conventional types 
of chucks such as power or scroll chucks having serrated master jaws of 
the type shown in FIGS. 7 and 8. In this form of the invention, many of 
the parts are the same or similar to corresponding parts described in 
detail with reference to the first form of the invention shown in FIGS. 
1-6, and corresponding numerals therefore are used to designate 
corresponding parts of the two forms. In this type of chuck, the master 
jaws 92 are moved radially of the chuck body (not shown) under power in 
any suitable or conventional manner and the top surfaces of the jaws are 
formed with transverse serrations 94. Only one jaw is shown in the 
drawing, but it will be readily appreciated that the type of chuck 
referred to has a plurality of chuck jaws (usually three) arranged 
concentrically about the chuck axis and in equi-spaced relation with 
respect to each other, similarly to the chuck shown in FIGS. 1-6. In these 
chucks, each master jaw 92 is conventionally provided with a radial T-slot 
96 having the usual head portion 98 and neck portion 100 that opens 
through the top surface 102 of the master jaw as in the Ball-Lok chuck. 
In order to adapt the master jaw 92 for use with a top jaw embodying the 
present invention, it is only necessary to mill or otherwise form a 
transverse slot 104 adjacent the outer end 106 of the jaw to accept and 
capture the radial flange 108 of an actuator screw 110. The latter is 
similar to the actuator screw 28 described in connection with the first 
form of the invention except that it is formed with only a single wrench 
receiving terminal portion 112 at the flange end thereof. As shown in the 
drawing, the T-slot 96 opens through the outer end 106 of the master jaw 
92 so that the bottom head portion 72 of the double T-nut 22 can be 
inserted into the T-slot from the outer end of the master jaw with the 
neck portion 76 of the T-nut in the stem portion 100 of the T-slot 96 and 
the upper head portion 74 of the double T-nut spaced above the serrated 
top surface 102 of the master jaw. A top jaw 20 similar to the one 
previously described except for the provision of a master key 114 recessed 
into the undersurface thereof behind the inclined T-slot 26. The master 
key has bottom serrations 116 that interfit with the master jaw serrations 
92 and it is detachably fastened to the top jaw 20 by a screw 118. 
From the foregoing, it will be readily appreciated that the top jaw 20 can 
be mounted on the master jaw 92 as in the form of the invention first 
described. As previously, the actuator screw 110 is threaded into an 
internally threaded hole 78 in the double T-nut 22 from the radially outer 
end of the T-nut; and the top jaw 20 is mounted on the master jaw 92 by 
sliding the top head portion 74 of the double T-nut 22 into the inclined 
slot 26 of the top jaw and engaging the serrations 116 of master key 114 
with the serrations 94 of the master jaw 92. Manifestly, in this type of 
chuck, the top jaw 20 can be approximately positioned on the master jaw 92 
within incremental distances determined by the spacing of the serrations 
94 and 116. 
In use, the master jaw 92 is moved in the conventional manner to clamp and 
release a workpiece in the chuck. When the master key serrations 116 are 
interengaged with the jaw serrations 94, tightening of the actuator screw 
110 pulls the upper head portion 74 of the T-nut 22 against the bottom of 
the T-slot head portion 68 to lock the top jaw 20 securely in the selected 
adjusted position on the master jaw 92. Here again, the locking angles of 
the head portion 74 and the T-slot head portion 68 mutually cooperate with 
the lead angle of the screw thread that interconnects the T-nut 22 and the 
actuator screw 110 to hold the top jaw 20 securely on the master jaw 92. 
However, a turn or two of the actuator screw 28 in a direction to loosen 
the double T-nut 22 and advance the top head portion 74 thereof in the 
inclined T-slot head portion 68 permits the outer end of the top jaw 20 to 
be lifted sufficiently to disengage the master key serrations 116 from the 
master jaw serrations 94 so that the master jaw 20 can be pulled radially 
outwardly off of the T-nut 22. A substitute top jaw adapted for a 
different size or form of workpiece can then be slipped onto the 
projecting top head portion 74 of the T-nut 22, the master key of the 
substitute jaw engaged with the master jaw serrations 94 in the desired 
radially adjusted position of the top jaw, and the latter locked securely 
in place by turning the actuator screw 110 to tighten the T-nut head 
portion 74 in the top jaw T-slot head portion 68. 
In FIG. 7, the top jaw 20 is adapted for external chucking. This requires 
that the inclined T-slot 26 open through the radially inner end of the top 
jaw, that the master key 114 be disposed behind or at the radially outer 
end of the T-slot 26, and that the double T-nut 22 be disposed with the 
outer head portion 74 thereof at or adjacent to the inner end of the 
master jaw and radially inwardly of the master key 114. 
In order to adapt the chuck for internal clamping, it is necessary to 
reverse the top jaw 20 and the double T-nut 22, as shown in FIG. 8. In the 
case of internal chucking, however, it is desirable to have left hand 
threads on the actuator screw 110 and in the double T-nut 22 so that the 
actuator screw is turned clockwise in the normal manner for locking the 
top jaw 20 on the master jaw 92. 
FIG. 9 shows the top jaw mounting arrangement of this invention adapted for 
use with a conventional chuck of the type having master jaws 120 formed on 
the outer faces thereof with step-along serrations 122. This form of chuck 
and jaw mounting is similar to the one shown in FIGS. 7 and 8 and the same 
numerals therefore are used to designate corresponding parts or 
substantially corresponding parts in the two structures. The serrations 
122 extend transversely of the master jaw top surface in the same manner 
as the serrations 94 shown in FIGS. 7 and 8. However, in the type of chuck 
shown in FIG. 9, the serrations 122 conventionally are V-shaped with the 
individual serrations usually spaced approximately 1.5 mm apart and the 
surfaces of the individual serrations disposed at an included angle of 
approximately 60.degree.. When adapting the top jaw mounting of this 
invention to the type of chuck involved here, the bottom face of the top 
jaw 20 is serrated similarly to the top surface of the master jaw 120 so 
that the entire mating surfaces of the two jaws are utilized to hold the 
top jaw in its selected radially adjusted position. As a consequence, it 
is not necessary to use a master key such as the one shown at 114 in FIGS. 
7 and 8. It will be readily apparent, however, that in the chuck shown in 
FIG. 9 the top jaw 20 is locked in a selected radially adjusted position 
on the master jaw 120 in the same manner as in the chuck shown in FIGS. 7 
and 8 simply by tightening the actuator screw 110 in one direction to draw 
the upper head portion 74 of the double T-nut 22 tightly against the 
underlying surface of the T-slot head portion 68, and that the top jaw can 
be similarly released for replacement simply by rotating the actuator 
screw 110 a turn or two in the opposite direction to loosen the outer head 
portion of the T-nut sufficiently so that the serrations on the top jaw 
can be disengaged from the master jaw serrations and the top jaw tilted 
slightly and slipped radially off the T-nut. It will be apparent also that 
a substitute top jaw can be mounted on the master jaw simply by reversing 
the above operations. Manifestly, the chuck shown in FIG. 9 can be adapted 
for either internal or external chucking in the manner described for the 
chuck shown in FIGS. 7 and 8. 
While it will be apparent that the invention herein described is well 
calculated to achieve the benefits and advantages as hereinabove set 
forth, it will be appreciated that the invention is susceptible to 
modification, variation and change without departing from the spirit 
thereof.