Patent GB-830332-A (GB)
Title: Improvements in or relating to screw thread cutting devices
IPC: B23B31/08
Filed: 1956-03-16
Abstract: 830,332. Tapping &c. attachments; sockets. SVENSKA PRECISIONSVERKTYG A.B. March 16, 1956 [March 18, 1955], No. 8335/56. Class 83 (3). A screw-cutting attachment having driving and driven elements with a yielding clutch between them and yieldingly connected to one of them, has one or more auxiliary members which are displaced when the clutch yields and which form a continuous surface which prevents the clutch parts from re-engaging until the drive is reversed. In one form, the driving element 12 has recesses 68, Fig. 1, receiving conically-ended pins 74 axially slidable in recesses in a clutch-ring 60. Balls 88 are pressed by springs 82 against the pins 74 and normally transmit torque from element 12 to a flange 66 on the driven element 18 in which the tap is mounted. When the tap meets undue resistance, the increased-torque cams the pins 74 out of recesses 68, and element 12 rotates slightly, as limited by pins and arcuate slots, relatively to ring 60 so that pins 74 rest against the flat end-surface of element 12 to form a continuous surface therewith. The balls 88 are thereby depressed into flange 66 so that the driving element and ring 60 may continue to rotate whilst element 18 remains stationary. The limiting-torque may be adjusted by varying the compression of springs 82 by a screwedring 16. Relative rotation between elements 12, 18 is allowed by balls 22. On reverse rotation of element 12, the ring 60 is reversely rotated until the pins 74 re-enter the recesses 68 to rotate the tap in the reverse direction. In another form a ring 90, Figs. 4 and 7, is drivingly connected to driven element 18 and has peripheral recesses 98 engaging arcuate teeth 106 on driving element 12. Another ring 96, rotatable on ring 90 by balls 94, within the limits of a pin and arcuate slot, has recesses 100 normally aligned with recesses 98 and engaging teeth 106 so that the latter may drive element 18. On excessive torque, the teeth 106 depress rings 90, 96, due to bevelled surfaces 100<SP>1</SP>, against a spring 112. Since ring 96 is freely rotatable by the balls 94 it is carried round with element 12 until its pin 102 engages the end of the slot in ring 90, in which position the recesses 98, 100 are staggered to prevent entry of teeth 106, and the element 12 rotates freely. On reverse rotation of element 12, ring 96 rotates to its former position and teeth 106 enter the recesses to drive the tap reversely; if excessive torque in this direction is encountered, the teeth 106 ride out of the recesses with a ratcheting action. The limiting- torque in either direction is adjusted by rotating the abutment-nut 16 for the spring 112. In another modification the driving element 12, Fig. 8, has teeth 106 engaging teeth 108 in a ring 110 splined at 132 to an inner ring 112 rotatable by balls 118, within the limits of a pin-and-slot, on the tap-holder 18. The lower edge of ring 110 is plain, but teeth 124 on ring 112 engage teeth 126 on a ring 114 splined at 140 to holder 18 and pressed upwardly by springs 146, thus driving the tap. When a limiting-torque is exceeded, the teeth 106 displace balls 138, Fig. 11, from recesses 136 in ring 110, to depress ring 110, and consequently ring 114, the balls riding up inclines 111 to ensure that teeth 124, 126 are completey disengaged to stop the drive. On reverse rotation of element 12, the balls 138 ride into recesses 136 again to re-engage teeth 124, 126 and drive the tap reversely. Sockets.-The tap is held in an adapter 34, Fig. 1, secured to a sleeve 32 by a pin 36. The sleeve 32 is held in a socket 18 by a spring 38 which is partly extended by a stronger spring 46 to allow the tap to yield slightly on engaging the work. Axial movement between sleeve 32 and socket 18 is facilitated by balls 50 in a cage 52, which also locates a ball 54 to transmit torque by grooves 56, 58 from the socket to the sleeve. Specification 609,973 is referred to.