Patent GB-842285-A (GB)
Title: Improvements relating to machine tools
IPC: B24B47/04
Filed: 1958-03-25
Abstract: 842,285. Grinding. JONES & SHIPMAN Ltd., A. A., and HOULDSWORTH, J. March 3, 1959 [March 25, 1958], No. 9564/58. Class 60. A surface grinder of the kind in which a worktable is reciprocated relatively to the tool on a saddle automatically fed by a feed screw 14 transversely to the travel of the worktable at the end of each stroke of the worktable and before the return of the latter in reverse direction is provided with saddle feed mechanism comprising two pawl-and-ratchet gears of which the ratchets 1, 2, Fig. 2, are simultaneously rotated in opposite effective directions in response to the reversal of the worktables, and each gear has one pawl drivingly coupled with the feed screw 14 but so arranged that, when the two ratchets are rotated in response to one direction of table reversal, one pawl operates the feed screw in feed direction while the other pawl runs idly over the teeth of its ratchet in readiness for engagement on the next reversal of the ratchets when what was the driving pawl becomes the idler. The two pawls of each ratchet, Fig. 3, are movable in union into their engaged and disengaged positions by a setting device comprising a centre shaft 3, within the feed screw 14, which has a flat 5 near one end engagable by oppositelydisposed plungers 6, 7 which bear at their outer ends or the tails of the spring-loaded pawls 8, 10 ; when in contact with the flat the plunger allows one pair of pawls to engage their respective ratchet discs, one in the driving and the other in the idling position. The functioning of the pawls is controlled by rotating a knob 4, Fig. 2, at the external end of the centre shaft 3 to one of three angular positions, the first in which one plunger 7 is in contact with the flat 5, the second after 90 degrees of rotation in which neither plunger contacts the flat, both being extended by contacting the full diameter of the shaft 3, and the third, at 180 degrees, when the other plunger, 6, contacts the flat 5. Pawls 8 and 9 transmit a clockwise rotation of the ratchet discs to the feed screw 14 and pawls 10 and 11 rotate it in the opposite sense, the knob 4 thus being used to set the direction of feed or, in the intermediate position, to stop it or to permit of manual feed. Rotation of the ratchet discs is effected by a fluid pressure operated, double-headed piston 15, Fig. 1, having a rack 17 arranged, between the heads, transversely of the feed screw 14, the rack meshing with a pair of similar pinions 18, 19. The pinion 18 is secured directly to the ratchet disc 1, Fig. 5, the pinion 19 being keyed to a countershaft 20 and driving the ratchet-disc 2 in a reverse direction through a pair of equal gears 21, 22. The reciprocation of the piston 15 and rack 17 is effected at each reversal of the worktable by a valve mechanism described in Specification 549,936, the stroke being variable by an adjustable abutment 25, the position of which can be controlled by a screw 26 rotatable by a knob 30 and bevel gears 20, 27, to enable the extent of rotation of the ratchet discs 1, 2, and thus each step of saddle feed, to be set.