696,461. Grinding machines. RANSOMES, SIMS & JEFFERIES, Ltd., DYER, F. T., and REVETT, R. H. Oct. 17, 1952 [Oct. 19, 1951], No. 24495/51. Addition to 659,939, Class 60. [Also in Group XXIX] The feed carriage 41 of the grinding machine of the parent Specification is advanced and retracted by means of pressure fluid supplied to and exhausted from a hydraulic cylinder 300, Fig. 2, under the control of a valve 400 which is operable by hand to start and stop the carriage when desired and also automatically to stop the carriage at each end of its stroke. The carriage carries the traversing table 38 on which the worktable 34 is pivoted for operation as described in Specification 696,460. The hydraulic cylinder 300 is mounted in the machine frame 65 and has its piston rod 301 connected to a bracket 302 on the underside of the carriage 41. The valve 400 comprises a casing which has ports connected with a pipe 379, Fig. 10, for the supply of pressure fluid, pipes 371, 372 leading to opposite ends of the hydraulic cylinder 300, and pipes 380, 381, leading to an exhaust sump 190through, respectively, a speed-regulating valve 392 and gate valve 393. These ports are controlled by a piston valve 382 consisting of three pistons 383, 384, 385 on a piston rod which projects from the ends of the casing for contact with tappets 386, 387 on a slidable push rod 388, Fig. 2. An inward or feed stroke of the carriage is effected by pulling on a handle 421 on the rod 388 so that the tappet 387 shifts the piston valve 382 from its neutral position to one in which pressure fluid passes through the pipe 372, Fig. 10, to one end of the cylinder 300 and is exhausted from the opposite end of the cylinder through the pipe 371, valve 400, and regulating valve 392 to the sump 190. The carriage is therefore advanced at a speed determined by the rate of passage of the exhaust through the valve 392. This valve consists of a casing 394, Fig. 7, provided with inlet and outlet ports 395, 396 and a piston valve 500 having a tapering slot 406 so co-operating with the outlet port 396 that the more the piston is depressed against an upwardly-acting spring 401 the greater the opening of the port 396 and therefore the speed of the carriage. The upper end of the piston projects from the casing 394 for actuation by a pivoted arm 402 having a roller 404 co-operating with a cam 405, Figs. 2 and 7, which is so curved as to provide for a more rapid feed at the ends of the stroke than intermediately; such an arrangement is necessary when dealing with workpieces of varying curvature and length, such as the mouldboards of plough bodies, which require that the rate of feed of the carriage 41 should be slower when the traversing table 38 is making long strokes than when making short strokes. At the end of the feed stroke of the carriage, a tappet 143, Fig. 2, on the latter engages a collar 342 on a slidable rod 134 and moves the latter so that a further collar 142 thereon strikes a collar 146 on the push rod 388, whereby the tappet 386 moves the piston valve 382 to its neutral position and the carriage is stopped; the movement of the rod 134 acts as described in the parent Specification to stop reciprocation of the traversing table 38 and raise the grinding wheel. By then pushing on the handle 421 the tappet 386 shifts the piston valve 382 into position to cause pressure fluid to pass through the pipe 371 to the cylinder 300 and exhaust therefrom through the pipe 372 and gate valve 393 so that the return stroke of the carriage occurs at a more rapid rate than does the feed stroke. The speed of the feed stroke may be varied by adjustment of the effective area of the slot 406 in the valve 392 by rotating the piston valve 500 by means of a hand-operated nut 415, Fig. 7, operating through a screwed rod 414 and lever 407.