KEYLESS CHUCK

A keyless chuck (10; 301) comprises a jaw housing (28; 311) with jaws (32; 333, 335, 337) which are slidably mounted in guideways (40; 319, 321, 323) between a rearward opened position and a forward closed position. A jaw thrust member (34; 345) is coupled to the jaws and is slidably mounted in the jaw housing to apply a thrust force to the jaws and to maintain the jaws in the same relative axial location. A nut (42; 355) is fixed to the jaw housing and has a threaded opening (46; 357) coaxial with the chuck axis (Ax). A threaded spindle (48; 305) is engaged in the nut opening and is movable forwardly to apply clamping force to the jaws and rearwardly to remove clamping force. The spindle preferably engages the jaw thrust member through a small area contact patch (72; 401) to limit operating friction. The jaws either may be opened and closed responsive to rearward and forward movement of the spindle respectively or to simplify loading of a bit in the chuck, may be spring biased forwardly to a closed position (self-centering) and thus not movable responsive to movement of the spindle. A lock mechanism (22, 104, 42; 309) is preferably provided to limit relative rotation between the nut and spindle to prevent the application of excessive clamping force and to limit removal of clamping force. The lock mechanism also preferably permits incremental self-tightening when in the locked position through an automatic tightener (397) and through the sizing and spacing of two sets of teeth (373, 375) to limit the application and removal of clamping force on a drill bit. To limit the run out in a finished chuck, deformable (during assembly) interfaces (204; 401) are preferably provided between the jaw housing and nut and between the spindle and jaw thrust member (stop). To further enhance the accuracy of assembly and to reduce run out, the spindle and nut preferably have a smoothed walled interface (415, 417) to accurately control coaxial alignment of the nut and spindle.