Patent GB-952899-A (GB)
Title: Torque control device for power screw drivers and the like
IPC: B25B23/14
Filed: 1961-04-10
Abstract: 952,899. Screwing up and unscrewing screws. SKIL CORPORATION. April 10, 1961 [April 11, 1960], No. 12783/61. Heading B3N. [Also in Division F2C] A nut running or screwdriver attachment 5 for a power tool comprises a casing 14 screwed to an adaptor 11 secured to e.g. an electric drill 6. A hollow spindle 16 supported in the casing for rotational and axial movements is selectively driven from the drill spindle 13, through a torque control clutch 21, 23 and a second clutch formed by three dogs 45 on a member 43 which engage dogs 45 on member 23. Member 43 is urged to the right by a spring 52 and has three equi-spaced grooves 46 which carry sets of balls 47 in driving engagement with grooves 48 in spindle 16 and a counterbore 50 in member 43 is periodically engaged during operation of the attachment by three latching balls 51. Clutch 21, 23 is urged into engagement by a spring 20, adjustable by rotating a member 18 screwed into a slidable but non-rotary nut 30 which engages the spring. Three balls 36 are seated in deep dimples 37 in member 21 and engage in one set of shallower dimples 38 two sets of which are provided, so that when the resistance to rotation of spindle 16 due to the tightness of the nut or screw being tightened reaches a predetermined value, balls 36 will be cammed out of dimples 38 and will move into the next set of dimples. Dimples 38, Fig. 8, are drilled on a slant, face 41 being normal to the face of clutch member 23, and face 40 being at an angle thereto to assist the ball camming action, thus the torque required to cam balls 36 out of the pockets is greater when unscrewing a nut &c., than when driving it. The end of spindle 16 has a hexagonal socket for receiving a hexagonal shaped screwdriver 55, the inner movement of which is limited by a shoulder 57 in spindle 16; and a detent 58 retains driver 55 against accidental removal. A sheath 64 slidable in member 18 is retained in the latter by a detent 66 and is urged into its outer position by a spring 71. Latching balls 51 are actuated to move into counterbore 50 by a spring spool 75 carried by a rod 74 having a plunger 72 for engagement with driver 55. In operation shaft 13 is rotated in a clockwise direction looking from the right of Fig. 2, thus rotating clutch members 21, 23 in the same direction, with the other members of the attachment remaining stationary. Sheath 64 is placed over the screw to be tightened and is pressed against it and moves to the right to compress spring 71 until driver 55 engages plunger 72. Further pressure moves plunger 72 to the right and driver 55 engages a shoulder 57 on spindle 16 and the latter is also moved to the right against a spring, 78. Spring 52 moves clutch member 43 until teeth 44 engage teeth 45 on clutch member 23 and spindle 16 along with driver 55 is rotated to drive the screw. When the screw is tightened balls 36 cam out of dimples 38 and clutch member 23 is moved to the left against spring 20, also clutch member 43 is moved to the left to allow balls 51 to move into counterbore 50. Balls 36 move into the next set of dimples 38 and clutch member 23 is again rotated during which time teeth 44, 45, are disengaged and the parts of the attachment other than clutch 21, 23, are stationary until pressure is removed from the fastener whereupon the springs move the parts to their original positions as in Fig. 2.