637,241. Trueing grinding wheels. AEPPLI, A. March 3 1947, No. 6052. Convention date, March 1, 1946. [Class 60] In a grinding-wheel trueing apparatus, the trueing operation is initiated, after a certain number of automatic re-settings of the grinding wheel to take up wear, by a counter which adds up the number of resettings. A motor 4 drives the grinding wheel 2 and, through reduction gearing rotates a shaft 8 on which is mounted a cam 9 engaged by a bell-crank lever 10. When the lever drops into the notch of the cam, one end 11 contacts the wheel or, if the wheel is sufficiently worn, contacts 12, 13 are closed by the other end of the lever. A coil 14 then withdraws a stop 15 from a friction clutch 16 and an eccentric 17 is rotated, causing a pawl 18 to rotate a ratchet wheel 19 by one tooth space so that a lead screw 20, Fig. 2, feeds the grinding wheel to take up wear. This cycle is repeated until all the wear has been compensated. A friction coupling having leaf-springs 21 connects the wheel 19 with a second ratchet wheel 22 on which is mounted an insulated disc 23 engaged by a lead-in brush 25 and having circumferentially-spaced contacts 24. After a certain number of movements of the wheel 19 by the pawl 18, a brush 26 engages one of the contacts 24 and a coil 29 is operated to close switches 31, 32 and a holding switch 33. At either end of the traverse of a carriage 47 carrying a gear-hobbing spindle, a dog 48 or 49 shifts a rod 51 to open one of two switches 27, 28 and to close one of two switches 52, 53 ; the contacts 31, 32 are, however, maintained closed by the holding switch 33. A coil 38 then rotates a lever 39 to close switches 35-37 and thus a coil 34 withdraws a stop 42 from a friction clutch 43 so that a crank 44 moves a diamond-studded trueing arm 45 once over the wheel. Actuation of the coil 34, however, opens a switch 30 and thus coil 29 is deenergized, contacts 31-33 are opened, coil 38 is de-energized and the lever 39 tends to move away from the coil 38 under the action of a spring 57 behind a plunger 56. This movement is retarded, however, by the closing of a ball valve 60 so that fluid can be drawn into the space behind the plunger only through a narrow bore 59 and, before the movement is completed and, because of the lost-motion coupling 135, before the switches 35-37 open, contacts 12, 13 will have closed again and also switch 62 so that a coil 41 closes a switch 40 and energizes coil 38 to shift the lever 39 again. While switch 35 is closed, coil 63 is energized and holds a stop 64 against the ratchet wheel 23 so that the re-setting operations to compensate for trueing of the grinding wheel are not counted by the wheel 23. When the end 11 of the bell-crank lever again contacts the wheel, the contacts 12, 13 fail to close, coil 38 remains de-energized, the lever 39 returns to its normal position, the stop 64 is withdrawn and the subsequent re-settings are counted by the wheel 23. At either end of the traverse of the carriage 47, the rod 51 also operates a valve 72 controlling the supply of fluid to a carriage-feed piston 69. When the lever 39 is shifted the plunger 56 cuts off the supply of fluid from a port 65 to a plunger 66 which is then pushed down by a, spring so that a pin 68 locks the valve and prevents traverse of the slide 47 during trueing of the wheel. The Specification as open to inspection under Sect. 91 describes also a modification, Fig. 4 (Cancelled), in which the trueing is carried out after a certain number of teeth in a gear have been ground, and a ratchet wheel 80 having spaced abutments 81 is rotated by a pawl 79 operated by a crank 78 on an indexing shaft 77. The abutments 81 operate a switch 83 which is the counterpart of the contacts 24, 26 described above and the stop 64, coil 63 and switch 35 are not fitted. A switch 84 allows the trueing operation to be started at any time. This subject-matter does not appear in the Specification as accepted.