A chuck comprises a body (10) rotatable about an axis (11) and at least one jaw (12) movable in a radial direction to clamp a workpiece in the chuck. At least one operating lever (14) is mounted on the body (10) and the, or each, lever is operable to move a jaw (12) radially. The, or each, lever is also movable axially with respect to the chuck body (10), to disengage from the associated jaw (12), enabling the associated jaw (12) to be removed simply and quickly from the chuck body (10) by movement in the radial direction.

BACKGROUND OF THE INVENTION 
The invention relates to chucks. 
DESCRIPTION OF THE PRIOR ART 
Our European patent application No. 81303746.2 relates to a form of chuck 
having a readily removable jaw or jaws designed to reduce production time 
lost during jaw changes, an important consideration with relatively costly 
numerically controlled machine tools. 
In the form of chuck to which European patent application No. 81303746.2 
relates, the or each jaw is first moved radially and is then withdrawn 
axially. 
The axial movement enables the jaws to move clear of an operating mechanism 
such as the lever 22 shown in FIGS. 7 and 9 of European patent application 
No. 81303746.2. 
OBJECT OF THE INVENTION 
It is an object of the invention to provide for rapid change of the jaw or 
jaws of such a lever operated chuck without the need to complicate the 
construction of the jaw or jaws themselves by providing for the jaw or 
jaws to move axially. 
SUMMARY OF THE INVENTION 
Accordingly the invention provides a chuck comprising: 
(a) a body rotatable about an axis; 
(b) at least one jaw movable in a radial direction to clamp a workpiece in 
the chuck; 
(c) an operating lever mounted on the body and operable to move the jaw 
radially, the operating lever also being movable axially with respect to 
the chuck body to disengage the operating lever from the jaw thus enabling 
the jaw to be removed from the chuck body by movement in the radial 
direction. 
Preferably the lever co-operates with an eccentric device, rotation of the 
eccentric device causing axial movement of the lever. 
The eccentric device may include a member which projects to a point 
adjacent an outer surface of the chuck, rotation of the member such as to 
move the lever out of its normal operating position causing a part of the 
member to project from the said surface of the chuck thus giving a visual 
indication that the lever is not in its normal operating position. 
Alternatively or in addition there may be provided electrical means to 
signal if a lever is out of its normal operating position. 
The electrical means may comprise an electrical proximity detector arranged 
to detect the condition of the eccentric device. 
The chuck may be arranged so that the lever can only be moved axially to 
disengage the lever from a jaw when the chuck is in the fully open or 
fully closed position, thus reducing the likelihood that the lever will be 
moved out of its normal operating position when the chuck is gripping a 
workpiece. 
The chuck may be such that a device obstructs the axially inner end of the 
lever, preventing it from moving axially inwardly, except when the chuck 
is in the fully open or fully closed position.

DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION 
The chuck shown in the figures comprises a body 10 rotatable about an axis 
11, the body having three jaws movable in a radial direction to clamp a 
workpiece (not shown) in the chuck. The jaws and their operation are 
identical, and so only one jaw 12 is illustrated. 
The jaw 12 comprises a base jaw which is generally T-shaped in 
cross-section, as best shown in FIG. 1. The jaw is slidable radially in a 
generally T-shaped slot 13 in the body 10, so that the jaw is movable in 
the radial directions illustrated in FIG. 2 by the arrows A. In use a top 
jaw (not shown) is mounted on each base jaw, and it is the top jaws that 
actually make contact with the workpiece. 
The object of the invention is to enable the base jaws, together with any 
top jaws carried thereon, to be rapidly removable from the chuck, so that 
they can be rapidly replaced by a different type of jaw if the chuck is to 
be used to carry out a different type of operation or grip a significantly 
different size of workpiece. 
Mounted within the chuck body, axially inwardly of the jaw 12, there is an 
operating lever 14. This lever has an inner end 15, an outer end 16, and a 
generally spherical intermediate portion 17. The intermediate portion 17 
engages within a sleeve 18 such that the lever can make limited rocking 
movements, rolling within the sleeve 18 on the generally spherical 
intermediate portion 17. 
When the chuck is in normal use, the outer end 16 of the lever 14 engages 
within a recess 19 in the jaw 12. Thus rocking movements of the lever 
control the radial inward and outward movement of the jaw. 
It will be appreciated that there is a separate lever 14 for each of the 
jaws. 
The way in which rocking movement is applied to each lever 14 is 
conventional and need not be described in detail. It is sufficient to say 
that a control member 20, which bears against the inner end 15 of the 
lever, can be moved radially inwardly and outwardly by means of an axially 
movable cylinder 21 which has a wedge face 22 co-operating with a wedge 
face 23 of the member 20. 
In order to change the jaws 12, the levers 14 are moved axially inwardly to 
the position shown in FIGS. 1 and 2, in which the ends 16 of the levers 
are clear of the recesses 19 in the jaws. 
Axial movement of each lever 14 is controlled by a pin 24 which projects 
eccentrically from a cylindrical member 25 arranged in the bore 26 in the 
chuck body 10. The pin 24 engages in a slot 27 provided in the 
intermediate portion 17 of the lever 14. Rotation of the cylindrical 
member 25 causes axial movement of the lever. 
During axial movement of the lever, the side of the lever opposite to the 
pin 24 is guided by a peg 28 which is screwed into the lever, the 
projecting end of the peg engaging in a slot 29 which is formed in the 
collar 18. 
A backplate 30 is provided which, as best seen in FIG. 2, obstructs the end 
15 of the lever in this embodiment except when the chuck is in the fully 
closed condition. In this condition, a hole 31 in the backplate is in 
register with the end 15 of the lever, so that the lever can carry out the 
neccessary inward axial movement. If an attempt is made to move the lever 
radially inwardly when the chuck is in any other position, the end 15 of 
the lever will abut against the backplate 30 and the movement will be 
prevented. This is a safety feature intended to reduce the risk that the 
levers will be moved radially inwardly, thus completely freeing the jaws, 
when a workpiece is being gripped by the chuck. 
When the jaws are to be changed, and the chuck is in the appropriate 
position, with the workpiece removed, a manual operating key 32 has its 
hexagonal cross-section shaft 33 applied to a mating driving hole 34 in 
the outer end of the cylindrical member 25. Rotation of the key 32 one 
half turn disengages the lever 14 and permits the corresponding jaw to be 
withdrawn and a replacement jaw inserted. Return of the cylindrical member 
25 to its original position re-engages the operating lever. 
The limiting positions of the cylindrical member 25 are defined by a pin 35 
which engages in a groove 36 which extends around part of the periphery of 
the cylindrical member 25. In addition, a spring loaded ball 37 is 
provided engageable in each of two circumferentially spaced apart recesses 
37a provided on the periphery of the cylindrical member 25. These cause 
the cylindrical member 25 to click into each of its two limiting 
positions, thus assisting the chuck operator to tell when the cylindrical 
member is correctly positioned. 
The outer end 38 of the cylindrical member 25 is angled to blend with the 
periphery of the chuck body when the associated lever is in its normal 
operating position. This then permits the end of the cylindrical member 25 
to be used to give a clear visual indication of the position of the 
cylindrical member 25 and hence the associated lever. When the lever is in 
the disconnected position, as shown in the Figures, part of the end 38 of 
the cylindrical member 25 is proud of the periphery of the chuck by a 
significant amount, as shown in FIG. 4, and this can readily be seen by 
the operator of the chuck. 
The invention is not restricted to the details of the foregoing embodiment. 
For example, an electrical proximity probe 40 may be positioned to detect 
the condition of the eccentric pin 24 and provide an electrical signal 
should any of the eccentric pins be in the position which indicates 
disengagement of the associated lever. When the chuck is in use on a 
machine tool, this electrical signal can be provided during the first few 
revolutions of the machine tool spindle and be used to stop the spindle 
rotation prior to acceleration to a speed which would be dangerous with a 
disconnected jaw. 
There is a further safety factor inherent in the embodiment described 
above, in that normal operation of the chuck is prohibited when any of the 
levers are in the disengaged position, since the associated jaw will not 
move when an attempt is made to open or close the jaws.