Patent GB-365744-A (GB)
Title: Improvements in and relating to bevel gears and to apparatus for cutting the same
IPC: B23F1/06
Filed: 1930-12-20
Abstract: 365,744. Toothed gearing. KLINGELNBERG, G. A., KLINGELNBERG, M., KLINGELNBERG, R. G., KLINGELNBERG, W. H., and KLINGELNBERG, H. W., (trading as KLINGELNBERG SÍHNE, W. F.), Berghausen, Remscheid, Germany. Dec. 20, 1930, No. 38469. Convention date, Dec. 21, 1929. [Class 80 (i).] Bevel gears having longitudinally curved teeth, for connecting intersecting or offset axes particularly in automobile rear axles, are made with their tooth arcs more sharply curved on the convex side 7 than on the concave side 10, leaving a crown or bulge over a zone 3, 4 of their length, which bulge may be located centrally or near either end of the teeth under control of an adjustment during manufacture. The meshed wheels are thereby free to shift in either direction without jamming while still maintaining a large contact zone. The gears are bobbed by moving a cutter 11, having teeth in the form of an outwardly concave rack, in the common plane of an imaginary basic crown wheel, the cutter being rotated about its own axis and simultaneously being given a swinging movement about the crown wheel axis. Due to the concavity of the hob, the thickness of its teeth measured along a rectilinear chord, gradually decreases from each end towards the centre and since each part of the length of the bevel teeth is cut by a particular part of the hob teeth, the tooth spaces in the bevel wheel are cut narrowest at the central part, giving the teeth the required bulge. The root surfaces of the teeth are cut convex and the tips are made so initially. The bevel wheels are hobbed in the machine shown in Fig. 8, the bevel blank 35 and the pinion 34 to mesh therewith being mounted on opposite, or the same ends of a work spindle 58 carried in a work headstock 48 vertically adjustable in a guide 57 rotatable through 360‹ about the vertical axis 61. The guide 57 is carried on a cross slide 62 carried on a longitudinal slide 63. The work spindle 58 is driven from a shaft 75 through bevel gearing 76, shaft 77 bevel gearing 78, 80, provided to allow the transverse movement of the slide 62, shaft 61, bevel gearing 81, change gearing between the shaft 82 and the shaft of a worm 84 driving an indexing worm wheel 59 on the work spindle. The hob 11 is supported at each end on a head 50 and is rotated about its own axis by a worm 52 driven through change gearing from a shaft 53 mounted in a plate 54 which carries the head 50 and is radially adjustable in a face plate 55 rotatable about the axis 65 and driven through a worm 56 to give the cutter 11 its swinging movement. The face plate 55 is mounted in a headstock 47 longitudinally adjustable in guides 49 to give the required depth of cut. The machine is driven from a belt pulley 64 which drives the shaft 53 rotating the cutter 11 directly through bevel gearing 66, 68, and also drives the work spindle rotating shaft 75 through a differential gear 72 and a shaft 73. The face plate 55 is driven through a worm 85 on the shaft 73, change gearing to a worm 88 engaging the planet carrier of the differential and further change gearing to the worm 56. The cutter head 50 has an adjustment about the axis 52 and also about the axis 53. The Specification includes mathematical calculations for setting the cutter to obtain the minimum spiral angle at the small diameter of the gear. For holding bevel gears with offset axes the work headstock 48 is adjusted vertically in the guide 57. The conical hob 11 is shaped in the machine shown in Fig. 4 being rotated through worm gearing and simultaneously carried along by a table 14 moved in guides 16 by a lead screw. The thread is cut by a milling cutter 19 carried by a slide 21 reciprocated in a guide 22 by a cam 25 to supply the normal backing off movement to the tool. The guide 22 is carried in a fixed guide 26 and in addition to the normal backing off movement, the tool is given a movement parallel thereto by a cam 12 driven through change gearing 29 by a rack 33 on the table 14 so that the milling cutter 19 follows the concavity of the hob surface. The surface of the control cam 12 may be parabolic or sinusoidal and the slides 21, 22 are pressed against their cams by spring or oil-loaded plungers. The surface of the hob is thereafter gashed axially to provide its cutting teeth. In order to equalize the wear throughout its length, in view of the teeth at the larger diameter being called upon to perform the greater share of the roughing work on the bevel blank, the cutting faces are undercut at the large diameter about 10‹, this angle gradually decreasing to zero at the small diameter. This variability is provided for by inclining the grinding wheel which forms the axial gashes, at a variable angle with respect to the cutter radius, this angle being controlled by a templet. Grinding allowances are provided in the bevel gears towards the tops of the teeth of the driving gear and the roots of the driven gear teeth, by using different hobs for cutting each gear, the hob for the driving gear having a more acute flank angle than that for the driven gear. Specifications 208,177, [Class 83 (iii), Metals, Cutting], and 220,027 [Class 80 (i), Gearing, Belt &c.], are referred to.