GB871020A - Improvements in or relating to the manufacture of cast worm wheels - Google Patents

Abstract

871,020. Copy-milling; casting; moulds; making worm-wheels and moulds therefor. HATCH, J. A. July 12, 1957, No. 22216/57. Classes 83 (1), 83 (2) and 83 (3). A method of manufacturing a worm-wheel consists in casting the wheel in a mould consisting of several machined metal segments. A mould segment B slides on a bracket 29 and is attached to a sector 46 rotatable by a worm 25 about an axis WH representing the axis of the worm-wheel to be cast. The bracket 29 is vertically adjustable on a cradle 5 rotatable by gearing 87, 88 about an axis WO representing the axis of the meshing worm. The cradle is mounted on a bracket 1 supported on a vertically and horizontally movable slide M. The position of the bracket 29 is adjusted by moving the slide M and by moving the worm 25 axially on its shaft 17. The blank is secured to the sector 46 by a locating screw 50 passing through one of a series of holes 47. When the shaft 17 or the shaft 10 of the cradle 5 is rotated, interconnecting change gearing 76 causes the shafts to rotate at a selected ratio and the tool T to cut a tooth space of the correct lead on the blank. The shaft 17, Fig. 9, may be rotated from a power- or hand-driven shaft 92 through gearing 104, a shaft 106, gearing 118 and swinging arms 117, 127. Alternatively, the shaft 106 may be coupled to the shaft 10 and the arms 117, 127 omitted. The cutter T, Fig. 12, is mounted in a block 145 adjustable angularly on straps 141, 142 secured to an over-arm 140. A drawbar 166 secures the cutter in a spindle 148 supported against thrust and axial bearings 149, 160. The spindle is rotated by the machine spindle 170 through bevel gears 168, 163. The mould blanks are initially made by making slantwise cuts in a circular blank to produce eight sections. The sections are assembled as shown in Fig. 14, allowance being made in machining for shrinkage. The cutter may have a straight or involute profile, and may be tilted to vary the pressure angle. For setting-up purposes, a master pattern may be made by positioning a toothless wooden segment below a finish-machined master worm-wheel, pouring plaster into the spaces and machining a locating hole therein. The master is then mounted in the machine which is operated manually to move the master into contact with the stationary cutter. Adjustments are made until the cutter correctly follows the master contour. A blank is then cut, indexing being effected by moving the screw 50 into successive holes 47. When one side of all teeth of the blanks has been cut, the blanks are reversed and the other sides are cut. Alternatively, the blanks may each be finished at one setting by moving the cutter. The cradle may be counterbalanced and the cut always be taken in one direction to eliminate backlash. The cast worm-wheel may be hobbed or lapped or run-in or used directly as cast if lead is included in the bronze. Specification 871,021 is referred to.