SELF-ADJUSTING CHUCKS

Abstract: A self-adjusting chuck has a body (41), jaws (43) housed within the body and retractable to allow the insertion of a bit, the opening movement of the jaws being accomplished by the bit itself, means (42, 48) for ciamping the jaws against the inserted bit, and a drive fitting (52). Movement of a first member, which may be the jaws (43) or a separate member (44), to accommodate the bit relative to a second member (46) is such that a dimension between the two members remains constant. Also the clamping means (42, 48) apply a force at the remote end of the second member. The chuck may be for fitting to a power tool, e.g. a drill.

Description: SELS-ADJUSTING CHUCKS This invention relates to self-adjusting chucks, whether for hand-held tools or machine tools. Time taken in changing "bits" due to adjusting and tightening chucks, on hand-held power tools in particular, can be compounded with lost chuck keys and even injury if the drill or tool is accidentally started before the chuck key is removed. Keyless chucks are known but they suffer from an anomaly in that either they cannot be tightened sufficiently by hand or they take a longer -time to be adjusted than a chuck employing a chuck key. In the case of known chucks there is often a need to re-tighten the chuck during use due to the work-torque which is applied to the jaws causing vibrations to be transmitted directly to the jawclamping threads, resulting in the chuck loosening. The term "bit" is intended to include other tools besides drill bits which are required to be held in a chuck. According to the invention there is provided a self-adjusting chuck comprising a body, jaws housed within the body and retractable to allow the insertion of a bit, the opening movement of the jaws being accomplished by the bit itself, means for clamping the jaws against the inserted bit, and a drive fitting, characterised in that movement of a first member to accommodate the bit relative to a second member is such that a dimension between the two members remains constant, and in that the clamping means applies a force at the remote end of the second member. In a preferred form of the invention the first member is guided to rotate as it slides during retraction of the jaws and has a helical--shaped end remote from the jaws which maintains a constant spatial relation, or contact, with some part of a similar helical end of the second member, It is also preferred that the clamping means comprise means for locking the members together, if necessary after moving the second member into engagement with the first member and subsequently applying pressure to clamp the jaws onto the inserted bit. By way of example, specific embodiments in accordance with the invention will be described with reference to the accompanying diagrammatic drawings in which: Figure 1 is a section through a chuck; Figure 2 is a perspective view of one of the jaw operated cylinders of the chuck of Figure 1; Figure 3 is an exploded view of modified clamping means; Figure 4 is a section through another chuck; Figure 5 shows the jaws coordinating member of the chuck of Figure 4; Figure 6 is a perspective view of one of the jaws of the chuck of Figure 4; and Figure 7 is a section through the body and the surrounding sleeve of the chuck of Figu#re 4 taken along the line 7-7. Figures 1 and 2 illustrate diagrammatically a chuck having a one-piece body 1 and at one end a threaded spigot 2 forming a drive fixing for mounting the chuck in a power tool. ' Uhe jaws 3, which may be any convenient number, are housed in an appropriate cavity 13 in the other end of the body in a manner which allows the jaws to slide longitudinally of the body to accommodate bits 14 having different diameter shanks. Inward movement of the jaws is effected by the bit itself, and the outer ends of the jaws define a lead-in to assist insertion of the bit. ¯ The chuck is thus self-adjusting. Means for clamping the jaws 3 onto the inserted bit include two cylinders 4, 6 extending end to end along an axial bore within the chuck body 1. The adjacent ends of the cylinders 4, 6 have the same helical shape (only shown schematically in Figure 1) and teeth 15 which interengage when the cylinders are brought together to lock the cylinders against relative rotation. The cylinder 4 is also engaged by the inner ends of the jaws and a light spring 16 acts between the cylinders 4, 6 to apply pressure to the jaws via the cylinder 4 to close the jaws when the bit is removed. The cylinder 4 has a helical groove 7 having the same angle and length as the helical cylinder ends. Within the groove fits a peg 8 which a fixed in the chuck body 1 but, in this ernbod#ment, is provided with a compressible member 9 which allows the peg a slight movement towards the jaws. The provision of the peg and the groove will cause the cylinder 4 to turn during rearward movement of the cylinder. The other cylinder 6 has a slot 10 engaged by a second peg 11 which allows the cylinder a small degree of longitudinal movement, but not to rotate. In operation, if the jaws are pushed backwards by a bit, the cylinder 4 will be pushed inwardly, and will turn as it slides, whilst the cylinder 6 remains stationary. Hence the adjacent ends of the cylinders 4, 6 will turn past one another with a constant length of gap between them. Thinien the jaws are open enough for the bit shank to enter and pushing stops, there is still the same axial dimension of gap 17 between cylinders 4 and 6, whatever diameter of shank has been inserted. The cylinder 6 is then moved towards the cylinder 4 by rotation of a lever operated cam 12 until the teeth 15 engage and prevent relative rotation of the cylinders. Further pressure applied to the end of the cylinder 6 remote from the jaws, for instance by the cam 12 causes a force to be applied by the cylinder 4 against the jaws to make them grip the bit in the normal manner. The peg 8 can move forward slightly to allow for any strain as the stress on the cylinder 4, jaws 3, body 1 and bit 14 increases. Return movement of the cam releases the pressures, and peg 8 retracts cylinder 4 from any strain displacement and the bit 14 is freed for removal. The lever (not shown) for activating the cam extends parallel to the axis of the chuck and flush with the body 1 when this lever is in the clamping position. Figure 3 shows a different clamping arrangement having an additional cylinder 313 and a strong spring 314, or other compressible element, between the cam 12 and the cylinders 36, 34 which are equivalent to the cylinders 6, 4 respectively of the embodiment of Figures 1 and 2. The provision of the strong spring 314 in addition to the light spring 35 achieves a desired predetermined force between the pressure applied by the cam and the pressure applied by the cylinder 34 on the jaws and also a more constantly correct gripping force on the bit, regardless of any abrasion Qf the bit shank during use which would otherwise require rew tightening of the chuck. The embodiment of Figures 4 to 7la rsimilar in principle to the embodiment of Figures 1 and 2, The body 41 is again of one piece construction but in this case has a female drive fixing 5), The jaws 43 and cylinders 44, 46 are substantially the same as before (again the helical ends and groove are shown schematically for clarity) except that the cylinder 44 applies pressure to the jaws indirectly via a coordinating member 47. This member 47 (Figure 4) has three rebated grooves 50 for reception of equivalently shaped retaining elements 51 on the jaws 43 (Figure 5). The cam is also replaced by a bar 48 which extends through a transverse hole in the chuck body and an aligned slot in the end of the cylinder 46 remote from the jaws 45. This bar prevents the cylinder 46 from rotating and thereby allows the previously described slot 10 and peg 11 to be omitted. Axial movement of the bar 48 both to move the cylinder 46 into locking engagement with the cylinder 44 and cause clamping of the inserted bit is effected by a sleeve 42 which is in screwthreaded engagement with the chuck body. To assist rotation of the sleeve, both the sleeve and the body are provided with knurling 49. Since the basic adjustment of the jaws is effected by the bit itself, it is possible to clamp the bit with a small amount of rotation of the sleeve 42, e.g. one turn or less. Figure 7 shows the three milled slots 52 provided in the chuck body 41 for mounting the jaws 43. This particular arrangement allows the chuck body 41 to be produced by a single multioperation automatic machine. The invention is not restricted to the specific details of the embodiments described above. For example, the cylinders may be locked together against relative rotation by friction, in which case the cylinders need not have a separating gap when the clamping pressure is released. Also the cylinders may be replaced by wedgeshaped members, the motion of which maintains the inclined surfaces parallel to one another and maintains a constant distance between them at some point or points, which distance may again be zero if desired. In another embodiment, the same function is achieved by members, which may be the jaws them selves, which slide at an angle to the axis of the chuck body, and keep a constant dimension relative to a cone or pyramid which subsequently is caused to apply the clamping pressure to the jaws. The locking together of the members may be achieved by interengaging teeth or protrusions, or friction, or magnetic force, If desired unlocking movement of the jaw clamping mechanism may operate a switch, key or clutch to cut off the power source to the chuck. For example, loosening of the sleeve 42 could be arranged to depress a $witch protruding from the adjacent end of the power tool body. An advantage of each chuck described above is that it allows the bit changing time to be substantially reduced compared with conventional chucks, since the chuck is self-adjusting to the inserted bit, leaving just a quick clamping action to hold the bit tight. Also, the tightening thread or cam is not directly vibrated by the work torque and thus the chuck should not loosen during use and thereby require re-tightening. Moreover, a predetermined spring pressure can readily be used if necessary to maintain the jaw grip on the bit even if strain or abrasion has otherwise loosened it. Furthermore, whereas in each embodiment described above there is a one piece body, the construction may also be in the form of a two or more piece body. In this case the work-torque could be used for tightening the grip on the bit. This could be achieved, for instance, by the sleeve 42 in Figure 4 being in one piece with the drive fixing member 53, which together then screw on the remainder of the body 41, for the purpose of tightening the jaws. Such a construction would give the possibility of automatic jaw tightening.

Claims: CLAIMS: 1. A self-adjusting chuck comprising a body (41), jaws (43) housed within the body and retractable to allow the insertion of a bit, the opening movement of the jaws being accomplished by the bit itself, means for clamping the jaws against the inserted bit, and a drive fitting (52), characterised in that movement of a first member (44) to accommodate the bit relative to a second member (46) is such that a dimension between the two members remains constant, and in that the clamping means (42, 48) applies a force at the remote end of the second member. 2. A chuck as claimed in Claim 1, characterised in that the first member is the jaws (43). 3. A chuck as claimed in Claim 1, characterised in that the first member (44) is guided to rotate as it slides during retraction of the jaws (43) and has a helical-shaped end remote from the jaws which maintains a constant spatial relation, or contact, with some part of a similar helical end of the second member (46). 4. A chuck as claimed in Claim 1 or Claim 2, characterised in that the members are wedges having adjacent inclined surfaces which remain parallel to each other and maintain a constant distance between them at some point or points during movement of the first member. 5. A chuck as claimed in Claim 1 or Claim 2, characterised in that the first member slides at an angle to the axis of the chuck body and maintains a constant dimension relative to the second member which is a cone or pyramid. 6. A chuck as claimed in any one of the preceding claims, characterised in that the clamping means comprise means (15, 42, 48) for locking the members (44, 46) together, if necessary after moving the second member (46) into engagement with the first member (44), and subsequently applying pressure to clamp the jaws (43) onto the inserted bit. 7. A chuck as claimed in Claim 6, characterised in that the members (44, 46) are locked together by interengaging teeth (15) or protrusions, or friction, or magnetic force. 8. A chuck as claimed in Claim 6 or Claim 7, characterised in that the locking means includes an external sleeve (42) in screw-threaded engagement with the body (41), and an element (48) intermediate the sleeve and the second member (46) whereby tightening the sleeve applies said pressure to clamp the jaws (43). 9. A chuck as claimed in any one of the preceding claims, characterised in that the jaws (43) retract against the pressure of a spring (16) until the jaws are sufficiently open for the bit to slide between them. 10. A chuck as claimed in any one of the preceding claims, characterised in that the clamping means (12; 42, 48) include a compliant member (314) intermediate the application of the clamping pressure and the jaws (3). 11. A chuck as claimed in any one of the preceding claims, characterised in that the chuck is fitted to a power tool and the unlocking movement of the clamping means (12; 42,48) operates a switch, key or clutch to cut-off the power source to the chuck.

Inventors: WALTON, JEAN
Applicants: WALTON, JEAN
Application year: 1981
Main classification: B23B31
IPC codes: B23B31