589,283. Grinding-machines. RICKENMANN, A. Jan. 5, 1944, No. 159. [Class 60] In a screw grinding machine comprising a grinding-disc having thereon a number of annular grinding ribs arranged to grind simultaneously a number of thread convolutions, and mounted so as to be advanced in stages towards the work, which is reciprocated axially past the disc, a set of cam discs is provided slidable on a shaft driven in fixed relation to the work spindle and adjusted on the shaft to co-operate selectively with a feeler, the movements of which are transmitted by a lever and hydraulic piston to the slide carrying the grinding-wheel, whereby the wheel enters the rotating work at a predetermined time and for a predetermined number of revolutions of the work; the machine may be adapted for plunge cut grinding with short traverse of the work, or for long traverse grinding. The machine comprises a base 1, Fig. 1, upon which is slidable a work table 2 and a slide 3 carrying the grinding-disc S, the work being carried by a tailstock 5 and a headstock 4 in which is journalled a work spindle 11. The machine is driven by a motor through worm gearing 192, 193 on a shaft 191 upon which is slidable a, reversing clutch 19 engageable with gears 20 or 21 to drive a shaft 9. The shaft 9 drives the spindle 11 through bevel gearing 194, and also drives a lead screw 13 for traversing the work table 2 through change gears 12 and reverse gearing 470-474 operated by a sleeve 47 slidably keyed on the screw 13 and movable by a fork 475 actuated by a piston 46. The piston is controlled by valve mechanism 18 comprising a piston 22, Fig. 27, which actuates a lever 224 moving the sleeve 19, movements of the piston being controlled by a valve 23, Figs. 9 and 10, rotatable and axially movable in a cylinder, in the valve body 18, and connected by a conduit 48 to a pump P. Fig. 27. The valve is turned by a cap 381 carrying a handle 38 which may be set in positions A ... D corresponding respectively with grinding long left-hand threads, long righthand threads, plunge cut left-hand threads and plunge cut right-hand threads. The travel of the table 2 is controlled by a pilot piston 233 in the body 18, Fig. 8, having a notch in which engages one arm 271 of a lever 27 mounted on the base 1 on a shaft 26 carrying a handle 25, one arm 251 of which projects into the path of two dogs 24 adjustably mounted on the table 2, so that as the dogs strike the lever the pilot piston is moved to cause movement of the valve 23 to reverse the rotation of shaft 9 and screw 11. For plunge cut grinding the travel of the table 2 is small and the dogs are not used to effect reversal, this being effected by two cam discs 28, 29 adjustable on a shaft 33 and having faces spaced at an adjustable angle which actuate the lever 27 ; the shaft 33 may be clutched to a worm-wheel 32 driven by a worm 31 driven from the shaft 9. Simultaneously with the reversal of movement of the table 2, the direction of rotation of the lead screw is reversed, the movements of the valve 23 acting to connect appropriate conduits to move the piston 46 and the fork 475. The grinding disc S is carried by a shaft 6 in the slide 3, the slide being provided with a screwed sleeve 17, Fig. 3, engaging a screw 16 which may be rotated through gearing by a hand wheel 14 ; the slide also is movable by hydraulic means, comprising a piston 51 on the screw 16 working in a cylinder 52 in the base 1. Oil is fed to the cylinder by a conduit 54, valve 545 and conduits 541,143, 144, Fig. 13, to move the slide towards the work against the action of a return spring 210. Smooth movement is provided for by the use of a pin 57 in a bore 245, 246 in the screw, the pin having a head 248 which, near the end of the movement of the slide to the right, engages a stud 56 and thereby contracts the conical space Q, slowing down movement of the slide ; a similar action at the end of the reverse movement of the slide is provided by an annular groove 146 which is partly covered by the edge 1451 of the groove 145 in the screw 16. The stud 56 is carried by the arm 551, Fig. 4, of a lever 55 eccentrically mounted on a shaft 123 journalled in a support 250, and the arm 552 of the lever carries an adjustable follower 58 contacting the arm 592 of a lever 59 pivoted in the support 250. The other arm 593 of the lever 59 carries a feeler 61, which may be moved by a piston 249 against the action of a spring 260 to contact with any one of a series of cam discs 621-625 mounted on a sleeve 73 slidable on a shaft 63 ; the shaft 63 is rotated from the shaft 9 through gears 300, 641, shaft 64 and change speed gears 66, and the cams serve through the operation thereby of lever 55 to cause the grinding-wheel to be fed into and out of the work. The different strokes of the work are accompanied by different feeds, brought about by moving the sleeve 73 to bring appropriate cams into action, the sleeve being moved whilst the grinding disc is moving away from the work by means of a lever 75 actuated by a rod connected to an arm 87 on a shaft 86, with which co-operates a rotary valve 100 turned by a handle 95 to occupy positions E, F, G, corresponding respectively to automatic movement of the slide 3 to and from the work and automatic movement of the cam discs 621 ... 625, transverse feed of the slide 3 by hand, and stopping of the shaft 9 &c. The shaft 86 is rotated, to move the sleeve 73, by means of a rack 81, Fig. 10, slidably mounted on the piston rod 221 and movable by faces 226, 227 on the shaft, movement of the rack being limited by a pin 225 ; the rack operates a gear 82 attached to an arm 83 carrying a fluid-operated pawl 84, which may engage a ratchet-wheel 85 connected to the shaft 86. A second fluid-operated pawl 88 also is provided, the two pawls 84, 88 being operated by fluid from the valve 100 according to the position of the handle 95. The machine is stopped automatically after the desired number of strokes of the work by means of a lever 98 carried by a sleeve 106 on the shaft 86 and connected thereto in adjusted angular position by a disc 104 on the shaft carrying a pin 105 which may be engaged in any desired one of a series of holes 107 in a head 108 of the sleeve 106, after the shaft 86 has made the requisite number of angular steps to move the lever 98 so that a nose thereon engages a disc 99 on the valve 100 and rotates it to the stop position G, and also allows a stop 91 to move under spring pressure into a notch 93 in the piston-rod 222. The machine is started by moving the lever 95 to position E or F ; this withdraws the stop 91 from the notch 93 in the piston-rod 222, so that the piston 22 may move. Taps, milling cutters, &c. are ground and relieved in a cycle in which a tap &c. with four flutes is treated in four full turns of the tap, the grinding-wheel being fed whilst it passes over the flutes ; during each turn of the tap, the wheel makes four relieving movements, these being effected by a single cam which replaces the cams 621 ... 625 and is rotated to give four revolutions for one revolution of the tap. The feeding of the wheel is effected by step-by-step rotation of the eccentric shaft 123 from a disc 124 on a shaft 129 through levers &c. 130. When cutting threads on cylindrical pieces, the table 2 is reciprocated by the dogs 24, and the slide 3 and wheel S adjusted by hand or automatically ; when automatic feed is employed, the cam discs 621-625 are used, but are not rotated, the discs being moved to engage the feeler -61 with one of the discs to give the feed during the return stroke of the grinding disc. The grinding-wheel S is dressed or profiled by a roller 161 pressed into the wheel by hydraulic pressure, under control of a valve 152 operated by a lever 151, whereby a piston 156 in a cylinder 169 operates, through a link 157 and lever 158, a shaft 159 carrying the roller 161 on an arm 160. The pressure of the roller on the wheel is adjustable and indicated on a gauge 173, the reduction in diameter in the wheel being also indicated on another gauge ; during trueing the wheel is rotated slowly under control of a lever 174 which also operates a valve 155 to admit fluid to the cylinder 169.