Patent GB-562535-A (GB)
Title: Improvements in or relating to gear grinding apparatus
IPC: B23F23/12
Filed: 1943-03-25
Abstract: 562,535. Grinding gears. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. March 25, 1943, No. 4856. Convention date, March 25, 1942. [Class 60] [Also in Group XXII] In a machine for finishing hardened gears. having helical involute teeth by grinding, a grinding wheel with a flat operative surface is given a cycle rectangular movement in a plane containing, or parallel to a plane containing, the gear axis, the cycle of movements giving a cutting feed parallel to the gear axis for a distance approximately half the axial pitch of the teeth, a withdrawal away from the gear, a rearward movement opposite to the cutting feed, and an advance towards the gear to engage the corresponding flank of the succeeding teeth. The line of engagement of the wheel with the involute surface of a tooth, forming a chord of the wheel and reaching from the dedendum to the adendum of the tooth, thus sweeps out a rectangular surface a, a<1>, d<1>, d, Fig. 3, on the flank of a tooth 21 during the cutting feed and with continuous rotation of the gear about its axis together with a continuous feed of the wheel carriage parallel to the gear axis, a series of such rectangular surfaces is formed in overlapping helical disposition around the gear, producing one finished flank from end to end of each tooth during a rotation of the gear. The machine comprises a table 12, Fig. 4, rotatably carrying the gear 20 and adjustable to and from a pillar 11, to suit the size of gear, by means of a screw 14. Rotation of the table is caused by a worm drive and shaft 17. The pillar 11 carries a carriage 22, fed vertically by a screw 16 and having the cutter slide 32 connected thereto by a parallel motion linkage 23, Fig. 5, which controls the cyclic movements. Springs 97, 98, Fig. 6, take up backlash in the pivots of the linkage and serve to balance part of the weight of the slide. The cyclic movements are imparted to the slide by four cams such as 49, 50, Fig. 10, on a shaft 47 driven through a flexible coupling, the cams acting on flat surfaces 53-56 on the slide. The cam which produces the cutting feed operates through approximately 180 degrees to give a slow feed and the other three complete the cycle rapidly through the remainder of the revolution of the shaft. The grinding wheel 38, having a flat operative surface 41, and its driving motor 39 are mounted on a plate 40 adjustable on guides 42, 43 on a wedge-shaped bracket 35 angularly adjustable about a horizontal axis on the slide 32 to which the parallel motion linkage is attached. The wedge angle of the bracket 35 maintains the operative face of the wheel 38 at the pressure angle of the involute, being cut and angular adjustment of the bracket on the slide 32 places the face of the wheel at the helical angle of the teeth on the gear 20. The plane of cyclic movement of the wheel 38 and slide 32 is usually the vertical plane containing the gear axis, but it may be displaced parallel to the latter plane, in which case it must be adjusted to suit the diameter of the gear being cut in each instance. After completing one flank of each tooth in the gear 20, the bracket 35 is rotated about its horizontal axis through 180 degrees, thus setting the grinding wheel at the angle required for trueing the teeth on the other flank. Trueing cutting-wheels.-The grinding wheel 38 is trued periodically on its operative face 41 by a diamond 60, Fig. 6, adjustably held by nuts 64 on an arm 62 carried by a rock-shaft 63 rotatably mounted on the bracket 35 and biassed by a spring 71 to maintain the diamond outside the periphery of the wheel. A rod 73, Figs. 5 and 11, engages the free end of an arm 86 attached to the shaft 63 and normally is freely slidable through a bush 74 in the carriage 22 so that the diamond remains out of action as the slide 32 moves to and from the work. A disc 77 projects through a slot 75 in the bush 74 and is rotated a portion of a revolution during each cycle of movements of the slide 32 by means of a ratchet and pawl 79 having an arm 82 engaged by a plate 84 on the slide 32 each time the latter makes a downward feeding movement. After a predetermined number of cyclic movements by the slide 32, the disc 77 is rotated sufficiently to cause a dog 78 thereon to pass through the slot 75 and into a notch 76 in the rod 73, which is then in its retracted position as shown in Fig. 11. On the next rearward movement of the slide 32 away from the work, the rod 73 will be held stationary in the bush 74 and the shaft 63 will thereupon be rocked to cause the diamond 60 to be brought close to the axis of the grinding wheel 38. During this oscillation of the shaft 63, an arm 91 thereon carrying a pawl 92 rotates a ratchet 93 connected by gearing 96 to a screw 46 rotatable in the bracket 35 and engaging the plate 40. The latter is then moved upwards slightly in its guides 42, 43 to bring the operative face of the wheel 38 into contact with the diamond and thus restore this face to its true position to compensate for wear. During the next cutting feed of the slide 32, the disc 77 will be rotated to remove the dog 78 from the notch 76 and free the rod 73 so that the spring 71 may return the arm 62 and diamond outside the periphery of the grinding wheel, this transverse of the diamond across the face of the. wheel turning it to a plane surface.