GB1005230A - Improvements in or relating to a method and machine for cutting cam grooves in worms - Google Patents

Abstract

1,005,230. Grinding; copy milling. A. E. BISHOP. March 4, 1963, No. 8578/63. Headings B3D and B3K. A method of producing a cam groove 10a in a worm 10 for co-operation with a cam follower pivoted about an axis transverse to the longitudinal axis 20 of the worm comprises rotating the worm about its longitudinal axis, rotating a cutting member 35 in engagement with the peripheral surface of the worm and with the axis of rotation of the cutting member substantially parallel to the axis of the worm, and effecting relative rotation of the worm and cutting member about an axis 14a transverse to the longitudinal axis 20 of the worm and having the same relation to the longitudinal axis as the axis of the cam follower, the velocity of such relative rotation being varied to provide the cam groove as a helical groove of varying lead. In apparatus for carrying out the method, the worm 10 is mounted between centres 18, 19 in the arms 16, 17 of a bracket having a depending shaft 15 rotatably mounted in a trunnion 13 on a bed 12. One of the centres 19 is provided with a dog 23 in driving engagement with a pin 24 on the worm and is rotated by bevel gearing 31, 32 connected by a shaft 30, which is journalled in an extension of the bracket, to gearing 28, 29 driven by a motor 26 mounted on the bracket. A cam 50 is secured to the gear 29 and is engaged by a roller 51 mounted on an arm 52 extending from the trunnion 13 so that, as the worm is rotated about its axis, the bracket carrying the worm is rocked in timed relation about the axis 14a of the shaft 15. A spring 53 or hydraulic plunger maintains the cam and follower in engagement. The grinding wheel 35 is mounted on a shaft 37 supported at an angle corresponding to the helix angle of the groove to be ground on the worm by a pair of bearings 38, 39 on a slide 40 which is adjustable towards and from the worm by a screw 47 and supports a motor 45 connected by a belt-drive 46 to the shaft 37. In an alternative embodiment, the slide carrying the grinding wheel is rookable about the axis 14a by the cam 50 and follower 51. The cam may be formed so that the groove 10a in the worm has a smaller helix angle or higher pitch at its centre than at its ends or vice versa or have constant pitch. The grinding wheel may be used for rough or finish machining of the groove. Alternatively, an end milling cutter may be used for the initial roughing operation, the cutter rotating about an axis which is perpendicular to the axis of the worm and passes through the axis of rotation of the grinding wheel.