Patent GB-878396-A (GB)
Title: Improvements in metal cutting and like machines
IPC: B23B39/20
Filed: 1960-01-27
Abstract: 878,396. Drilling; tapping; turret lathes. BROWN & SHARPE MFG. CO. Jan. 27, 1960. [April 21, 1959], No. 2960/60. Class 83 (3). A machine tool comprises a tool-holder 78 and a work-holder, a spindle 26 rotatable at different speeds and attached to one of the holders, means 133, 140 for moving the spindle and the other holder relatively to and from each other, and second means 87, 102 for moving the spindle and the other holder relatively towards each other only, which latter means is operative during the final portion of the relative movement towards each other. The machine tool may be a turret lathe or turret-drilling machine with the work or tools or both being movable towards each other. In a turret-drilling machine having a vertically movable knee 20, the work WP is secured on a holder H on a horizontally movable table PT as described in U.S.A. Specification 2,880,632. A shaft 34 is rotated by a motor 39 through variable-speed pulleys 40, 41 and 35, 36, the former being adjusted by a yoke 43 moved by an air device 47 to positions determined by an indexible stop disc 49. The shaft 34 is connected to rotate the spindle 26 forwardly through a magnetic clutch 60 or at half speed in reverse through gears 51, 55 on a shaft 52 and a magnetic clutch 59. A switch 1SS may be operated by a dog 210 to cause the motor to run at low speed. The gears 55, in an oil-containing enclosure 29, act as a pump to force oil through a pipe leading to the gears 51. The shaft 52 carries a pulley 63 to drive a tachometer 66. The spindle 26 is carried by a quill 23 which is fed downwardly by a rack engaged by a pinion on a shaft 25 driven from a pinion 33 on the shaft 34 driving a belt 84, variable-speed belt gearing 87, 102, a shaft 107 and worm gearing 109, 111, 112. The variable-speed gearing is set by a lever 88 operated by an air device 95 cooperating with a setting disc 97 having adjustable stops 98, the disc being indexed with the turret 78 and the speed set being indicated on a tachometer. When the quill is fed downwardly, a lug thereon engages one of a number of stops 69 on a disc 68 indexible with the turret 78, which disc is moved downwardly by the lug against spring pressure until a downward limit switch is actuated to release a magnetic feed clutch connecting the worm-wheel 112 to the shaft 25. The shaft 25, Fig. 12, except for manual operation, is clutched by operation of a knob 120 to a shaft 116 carrying a gear 125. The gear 125 is driven by a double-toothed rack 127 either through teeth 127a or through teeth 127b, Fig. 11b, and gears 128, 132 to give a faster speed. The rack is attached by a rotary joint to a rod 133 carrying dogs 166 adjustable on a drum 163 indexible with the turret. The rod and drum can be moved axially by a projection 139 or a stud 137a on a rod 138 moved by a fluid-pressure device 140. The rod 138 is moved in one or other direction according to the setting of a feed valve. Movement of the quill and turret does not commence until the projection 139 engages a dog 166. During an advance movement of the turret towards the work, the speed is at first rapid until the abutment 139 actuates a switch LS-1 to engage the feed clutch and cause the feed speed to be effective from the belt gearing drive 87, 102. When the tool has been fed to the desired depth, the disc 68 is depressed and the downward limit switch is actuated to release the feed clutch and reverse the feed valve. The rod 138 then returns the rod 133 and the rack 127 to their initial positions, the movement at first being rapid while the rack teeth 127b operate and then slower as the teeth 127a operate. The slower speed drive gives a greater power to effect a disengagement of the operative tool from the spindle as described in Specification 764,671. The turret is indexed by a motor 190 driving through a one-revolution device and a Geneva mechanism, after a switch has been operated by the quill 23 at the upper limit of its travel. The Geneva wheel is disengageable from its shaft by a manually-operated plunger for manual operation. When one of the turret tools is a tap, a dog is set on the disc 68 to engage a switch to operate the motor 39 at a lower speed and to set a circuit for reversal of rotation, and an adjustable cam is set on the drum 163 to move throttle plungers in passages leading from the feed valve to cause a reduction in speed for the feed movement of the rack 127 with a doubled speed in the withdrawal direction. This doubled speed is combined with a doubled speed of tap rotation due to the operation of the lower limit switch causing the solenoid clutch 60 to be engaged. The belt gearing drive 87, 102 is not used during tapping. In manual operation, a hand-wheel 212 has slight lost motion which causes a switch to be actuated to reverse the tap when the handle is operated in the direction for withdrawal. In a modification, the rack 127 has only one set of teeth.