574,524. Grinding screw - threads. RICKENMANN, A. Dec. 3, 1943, No. 20219. [Class 60] A screw-thread grinding-machine is provided with automatic dressing-apparatus for the grinding-disc, wherein the traverse of the dressing-tool over the working face of the disc is derived from a single straight line motion effected by a fluid-operated motor, the traverse being subdivided into (1) an enveloping motion of predetermined radius and angle and comprising a number of short tangential oscillatory movements of the dressing-tool, to shape the rounded portion of the disc, and (2) a straight line motion on each side of the disc to shape the flanks of the working face and including several to-and-fro movements of the dressing- tool. The machine comprises a base 1 on which is slidable a carriage 2 carrying the work 5, the work spindle 6 being driven, through worm gearing 13, 14 and shafts 11, 12, by a shaft 101; the shaft 101 carries a slidable clutch member 9 movable by a lever 23 to engage either of two gears 103, 104, whereby the direction of rotation of the work is reversed, the direction of movement of the carriage 2, which is driven by gearing 7 and a screw 110 from the spindle 6, also being reversed. The lever 23 is actuated by a piston 21 movable in a cylinder 20, to which fluid is admitted by a reversing-valve 19, operable by electromagnets 18 controlled by a reversing switch 17 actuated by dogs 15, 16 adjustably mounted on the carriage 2. The valve 19 is fed by a pump P and its movements also control the flow of fluid from the pump to a cylinder 40, through pipes 38, 39; the cylinder 40 has therein a piston 41 provided with rack teeth engaging a gear 42 rotatable on a shaft 55, and carrying an arm with a pawl 44 thereon engaging a ratchet-wheel 45 fast on shaft 55. The shaft 55 has thereon a rotary distributing valve 37 controlling flow through pipes 35, 36 to a cylinder 32 on a slide 31 mounted on the grinding-wheel carriage 25, which is acted upon by a weight 30 to move the wheel 26 away from the work 5, the carriage being adjustable by a screw 28 carrying a hand wheel 27. The shaft 28 also may be actuated, through ratchet gearing 611, 64, 65 by a cam 57 on shaft 55 which engages an arm on the sleeve 611. The stroke of the piston 41, and hence the angle through which the valve 37 and shaft 28 are turned, is limited at one end by an abutment 47, and at the other end by any selected one of a series of pins 46, 461 ... 466 of different length carried by a gear 49 rotatable through a gear 50 by a knob 52, and the shaft 55 also may be turned by a hand wheel 60. The cylinder 32 has therein a piston 33 for, operating a dressing-tool 74, and is arranged on the slide 31 which is adjustable vertically by a screw 93, carrying a hand wheel 95 and a ratchet-wheel 92 with which engages a spring pawl 91 withdrawable by a knob 96. The pawl is rockably mounted in the slide and actuated by a pin 89, which is moved by bevelled faces 342, 343 on the rod 34 of piston 33 ; the piston is locked in its end positions by catches 97, 971, which are released when fluid is admitted to the cylinder. On the rod 34 is slidable a sleeve 68 having rack teeth 688 engaging a pinion 71 on a shaft 72 journalled in the slide 31 and carrying a casing 73, angular movement of which is limited by stop screws. This angular movement may be varied whilst the piston 33 always makes full strokes, as allowed by a spring 70 mounted between a shoulder on the rod 34 and a nut 681 on the sleeve 68. The rod 34 has thereon a tooth 69 co-operating with a cam plate 78 pivotally mounted on a shaft 79 and having cam faces 781... 785 engaged by the tooth ; the other face of the plate 78 has thereon a segmental row of teeth 791 engaged by a pin 801 on a block 80 slidable in the casing 73 and provided with a rack 81 engaging a gear 82 on a shaft 86, which gear also engages a rack 83 acted on by a spring 84. Movements of the pin thus oscillate shaft 86, which carries eccentrically the diamond 74; the shaft 86 is adjustable axially by a nut 87 screwing on the casing 73 and acting on a ball bearing 803 on the shaft 86. The casing 73 is oscillated by movement of the piston 34, and during this oscillation, the pin 801 passes over the teeth 791 and gives a vibratory movement to the tool 74; in addition, the plate 78 is rocked and the pin 801 displaced as determined by the cam faces 781 ... 785, movement of the tooth 69 over the face 783 corresponding to movements H of the tool 74, Fig. 15, whilst as the casing 73 oscillates from one stop to the other, the edge of the grinding-wheel is rounded off to the radius r. When the faces 782, 784 are engaged by the tooth 69, the tool 74 is swung over the flanks E, F of the wheel, the cam faces giving three swings of the tool; when the tooth engages cam faces 781, 785, the tool 74 is moved out of contact with the'grinding-wheel and the bevelled parts 342, 343 may actuate the pin 89 to feed the tool 74. The valve 37 is arranged so that a half rotation thereof is necessary to cause reversal of the piston 33, this corresponding to a full stroke of the piston 41 ; by placing a selected pin 461 ... 466 to limit the stroke of the piston 41, the number of strokes of the table 2 before the tool 74 becomes operative may be determined. The cam 57, through the ratchet-wheel 65, advances the carriage 25, when the tool 74 is out of contact with the wheel 26, by an amount to compensate for the wear of the wheel.