Counterbalanced chuck

Counterbalanced mechanism for a jaw chuck. There is provided for an otherwise conventional multi-jaw chuck suitable mechanism for independently balancing each said jaw. In a preferred embodiment, a pin is pivotally fixed at one of its ends into each master jaw, pivoted to the chuck body intermediate its ends and pivotally related at its other end to a radially movable counterbalancing mass. Each said mass and jaw are so related to the lever pin upon which they operate that they create balancing moments when the centrifugal force acting on each is equal and, due to the geometry of the apparatus, said moments remain sufficiently close to equal at any speed of operation of the chuck that a substantial balancing of the parts is obtained. Thus, whether the chuck is inside gripping or outside gripping, it can be properly adjusted in a normal manner at a standstill and the pressure of the chuck onto the workpiece will not materially change within the range of any normal operating speed.

FIELD OF THE INVENTION 
The invention relates to jaw chucks and particularly to an otherwise 
substantially conventional jaw chuck which is effectively counterbalanced 
in such a manner that the pressure of the chuck jaws onto the workpiece 
will remain substantially constant even though the rotative speed of the 
chuck changes through a normal range of operating speeds. 
BACKGROUND OF THE INVENTION 
It has long been recognized that in any jaw chuck arrangement operating at 
other than relatively low rotative speeds, the centrifugal force developed 
on the chuck jaws as rotative speeds increase may cause an appreciable 
change in the force by which the jaws engage the workpiece. Accordingly, 
where the jaws are arranged for inside gripping, an increase in rotative 
speed will increase the centrifugal force applied by the jaws to the 
workpiece and may effect a substantial distortion of the workpiece. This, 
particularly with relatively thin workpieces, often requires that the 
operating speed of the chuck be kept much below the speed at which cutting 
could otherwise be carried out with a resulting increase in the time 
required for a given operation and consequent greater expense. Conversely, 
where the chuck is arranged for outside gripping, centrifugal force will 
tend to diminish the force by which the chuck grips the workpiece, even to 
such a point that if the workpiece is subjected to substantial cutting 
pressure, it may slip in the chuck. This, again, often requires the 
operating speed of the chuck to be held below what would otherwise be 
possible. 
This problem has long been known and several types of counterbalance chucks 
have in the past been offered. These, however, have usually been either 
relatively complex, requiring parts having close dimensional tolerances, 
and requiring precisely constructed means for evenly applying a 
counterbalancing force onto each jaw. These chucks have been truly 
effective for only a narrow range of speeds and tend at other speeds to 
distort the workpiece to an undesirable extent. They also have other 
disadvantages well known to the trade. 
Accordingly, the objects of the invention include: 
1. To provide a counterbalanced chuck as above set forth wherein the 
counterbalancing means is effective in a substantially constant manner at 
all normal operating speeds of a given chuck, whereby the force by which 
the chuck engages the workpiece will remain substantially constant 
throughout the entire range of normal operating speeds for such given 
chuck. 
2. To provide a device, as aforesaid, which will constitute only a simple 
alteration in a wide range of otherwise standard chucks. 
3. To provide apparatus, as aforesaid, which is simple and may be added to 
a wide range of otherwise standard chuck designs with only simple and 
inexpensive modifications thereof. 
4. To provide apparatus, as aforesaid, wherein the changes required from 
otherwise standard chuck designs may be applied without adversely 
affecting the operation of the chuck. 
Other objects and purposes of the invention will become apparent to persons 
acquainted with apparatus of this general type upon reading the following 
specification and inspection of the accompanying drawings.

SUMMARY OF THE INVENTION 
The invention contemplates the provision for each jaw of the jaw chuck of a 
pin pivotally suspended onto the chuck body at a point intermediate the 
ends of such pin and having one end thereof pivotally connected to a 
radially movable jaw of the chuck and the other end of the pin pivotally 
connected to a radially movable counterweight. The relative masses of the 
jaw and counterweight are proportioned to the relative lever arms upon 
which they operate with respect to the pivotal support of said pin that 
same are in substantial balance regardless of the rate of rotation of the 
chuck throughout normal ranges of operating speeds. It is recognized that 
as a chuck jaw moves in one radial direction and the counterweight moves 
in the opposite radial direction the relative radii will change slightly 
and thereby somewhat change the centrifugal force acting upon the chuck 
jaw and counterweight, but these changes are sufficiently minor within the 
range of normal changes in operating speed that same can be tolerated and 
not interfere appreciably with the effective operation of the apparatus. 
DETAILED DESCRIPTION 
Referring now to the drawings in more detail, there appears in FIG. 1 a 
front elevational view of a chuck which insofar as this view is concerned 
may be any of several standard constructions, such as that of the chuck 
shown in U. S. Pat. No. 3 252 710. For convenience in understanding of the 
present invention, such chuck will be briefly described herein and 
reference made to said patent for such further details as may be desired. 
Referring therefore to the drawings, there is provided a generally 
cylindrical chuck body 1 having a rearward opening 2 for the reception 
thereinto of a conventional mounting flange, same being fixed to the chuck 
body as shown in the above-mentioned patent, by screws extending thereinto 
from the front of the chuck through a plurality of openings, of which one 
such appears at 3. A plurality, here three, of radially arranged slots 4 
communicate into a central opening 6 which in this embodiment is connected 
to the recess 2 by a further central opening 7. A plurality of master jaws 
8A, 8B and 8C each bearing appropriate means, here indicated as teeth 9, 
for carrying conventional top jaws (not shown) are slidably arranged in 
said slots. Each of said master jaws 8 terminates in a suitably sloped 
wedge follower 11 which is in turn engaged by conventional wedge means 12 
formed as part of a slider 13. Said slider 13 is supported, as is 
conventional, for axial movement on and by the cylindrical surface 15 of 
the usual internal opening in the chuck body and is in dust sealing 
contact with a dust sleeve 14. Said latter is fixed by any convenient 
means such as the screws 16 to the top plate 17 which is in turn fixed, as 
by the screws 18, to the chuck body 1. Said slider 13 may be axially 
operated in either direction in any convenient conventional manner, such 
as by a drawbar, not shown, extending through the opening 7 and fixed to 
said slider 13. 
All of the foregoing is conventional, forms no part of the present 
invention as such and is given only to illustrate the environment in which 
the invention operates. Further, it is given only as an example of typical 
chuck to which the invention may be applied and it will be recognized that 
the invention may be applied to a variety of other specific chuck 
constructions provided only that same utilize radially movable jaws for 
engaging and disengaging a workpiece. 
Turning now to the construction embodying the invention, and referring to 
the jaw 8A, there is provided a radially aligned opening 21, same being in 
this embodiment spaced from but in axial alignment with the one of the 
slots 4 occupied by jaw 8A. In this embodiment, though not necessarily, 
said opening 21 extends all of the way through to the central opening 7. A 
further opening 22 is provided for connecting the slot 4 with the opening 
21. If desired, and preferably, a wear bushing 23 may be provided as a 
liner for the opening 22. A counterbalance weight 24 is positioned 
slidably in the opening 21 and is provided with an opening 26 therethrough 
which is axially parallel to the axis of the chuck. A lever 27 is received 
at one end into a suitable slot 28 in the bottom of the master jaw 8A and 
preferably is provided with a spherical knob 29 at said end for effecting 
contact at the same point on the wall of the opening 28 in any normal 
pivoted position of the said lever in order to provide a lever arm of 
substantially constant length from said contact point with the master jaw 
8A to the pivot center of the lever 27. Similarly, said lever is provided 
with intermediate spherical knob 31 for contacting the wear bushing 23 and 
doing so at substantially constant points thereon by which the point of 
pivotal support of said lever likewise remains substantially constant 
regardless of the angle or position of said lever. Adjacent the other end 
of said lever there is provided a further spherical knob 32 engaging at 
least one wall of the opening 26 and again the shape of said knob is to 
effect contact at a substantially constant point on the walls of the 
opening 26 regardless of the angular position of said lever to insure that 
the lever arm from such point of contact to the center of pivoting of the 
lever remains substantially constant in all positions thereof. Identical 
levers and mounting and receiving means therefor are provided for each of 
the other master jaws 8B and 8C of the chuck in the same manner as above 
described. 
OPERATION 
Turning now to the operation of the apparatus, and assuming for the moment 
that the chuck was designed on the assumption of the lever 27 having a 
normal or base position parallel to the central axis of the chuck, it will 
be recognized that the moment generated by the mass of the master jaw 8A 
together with that of the top jaw carried thereby about the theoretical 
pivot center 30 may be caused by appropriate design to balance the 
corresponding moment of the counterweight 24 about the same theoretical 
pivot point. Further, assuming that same are in actual balance when the 
lever 27 is aligned parallel to the central axis of the chuck, such 
balance will remain effective regardless of the speed of rotation of the 
chuck. This balanced relationship can, of course, also be provided by 
appropriate design for any other desired base position of the lever 27. 
As the master jaws are moved outwardly or inwardly from said base position, 
the radius upon which the parts revolve will change slightly and thereby 
inversely change the centrifugal force acting upon such radially movable 
parts. However, such movement is relatively slight within the normal range 
of rotative speeds experienced by chucks of this nature. Whatever 
unbalance is created by such radial adjustment is of minor nature and can 
be tolerated. 
It will be observed that the construction required for providing the 
counterbalance of the invention can be readily incorporated into a 
standard chuck inasmuch as the openings 21 can be drilled from the outside 
of the chuck into the central opening 7 thereof. The opening 22 may be 
easily drilled through from the slot 4 and the slightly enlarged portion 
thereof receiving the bushing 23 may be similarly drilled. The slots 28 
may be cut into the bottom of any standard master jaw in a simple manner 
and the parts are ready for assembly as shown. None thereof are required 
to be of other than normal tolerances and since each counterbalance acts 
independently of each other counterbalance-jaw system, it is not necessary 
that exact uniformity be maintained for all of said systems. Substantial 
uniformity, however, is, of course, desirable in order to avoid excessive 
unbalancing and consequent vibration of such chuck particularly when 
rotating at a high speed. The parts may also be readily replaced as they 
wear and the chuck thereby easily maintained at all times in good 
operating condition. 
It will be recognized that the invention may be easily applied to a wide 
variety of specific chuck designs. Particularly, although three jaws are 
here shown, the invention is applicable to a chuck having any number of 
radially movable jaws and although it has been indicated above that the 
wedge 12 operates in response to a drawbar, it will be evident that same 
may also be operated hydraulically insofar as the present invention is 
concerned if desired. 
While the lever 27 is shown as lying in a plane which is axial of the chuck 
structure, and it is one of the advantages of the invention that such an 
alignment of the lever may be obtained, it will be recognized that at 
least some of the broader aspects of the invention may also be obtained by 
a generally similar counterbalance arrangement positioned with said lever 
27 arranged parallel with the face plate 17. 
Although a particular preferred embodiment of the invention has been 
disclosed in detail for illustrative purposes, it will be recognized that 
variations or modifications of the disclosed apparatus, including the 
rearrangement of parts, lie within the scope of the present invention.