Patent GB-284718-A (GB)
IPC: B23F5/12
Filed: 1928-02-03
Abstract: 284,718. Gleason Works, (Assignees of Wildhaber, E.). Feb. 4, 1927, [Convention date]. Gear-cutting. - In skew toothed gearing, each of a pair of gears is produced by moving a tool across a rotating tapered blank while simultaneously imparting an added relative rotation between the tool and blank about an axis offset from the blank axis. Preferably, a tapered pinion and a bevel gear gearing therewith are formed by a generating-process in which planing-tools represent the teeth of a basic crown wheel, which is either a true crown wheel with a plan pitch surface or a nominal crown wheel with true crown wheel with a plane pitch surface, the said teeth being longitudinally straight and preferably radial and with straight or fiat profiles. The pitch plane 16, Figs. 1 and 2, of the imaginary true crown wheel 17, of which the radial tooth 18, 19, centre 20, and axis 24 are shown, lies tangent to the conical pitch surfaces of the wheel 11, with axis 14 and apex 15, and pinion 10, with axis 12 and apex 13, so that the crown wheel can gear both with the wheel and with the pinion. The points 13, 15, 20 all lie in the plane 16. The point 22 is the theoretical point of contact in the plane 16 of the pinion 10, wheel 11, and basic crown wheel 17. The lines 14<1> and 12' are the projections of axes 14 and 12 in the plane 16, and the line 23 is the direction of the tooth of the wheel 17 at the point 22. Calculations are included in the Specification to show that, if it is desired that the points of the pinion, wheel, and crown wheel which will come into contact lie on a line perpendicular to the general direction of the crown gear teeth in the neighbourhood of the point 22, A2 tan h tan p = A, tan H tan P, where A1, A2 are the distances 13-22 and 15-22, h, H are the tooth inclination or spiral angles 13, 22, 20 and 15, 22, 20 of the pinion and wheel, and p, P are the pitch angles of the pinion and wheel, that is, the angles between the axes 12 and 14 and the plane 16. As this equation is independent of the radius 20-22 of the basic crown wheel, this radius may be so selected as to produce any desirable longitudinal mismatch between the tooth surfaces of the gear, preferably such that the same mismatch results on both sides of the teeth In Specification 251,953 it is indicated that the gears should mesh substantially along the line 12'. In the present invention, the line of mesh preferably passes from the point 22 between the lines 12<1>, 23, the inclination i from the line 12<1> being obtainable from the formula cot i = cot (H + h) + N cos p/n cos P sin (H + h) where N and n are respectively the numbers of teeth in the wheel and pinion. From a geometrical construction and a mathematical calculation based upon this assumption, the relation between quantities A1 and A2 for use in the firstmentioned equation is determined. In the case of mitre gears, the line of mesh lies midway between the lines 12', 23. Fig. 10 shows diagrammatically an elevation of an apparatus for cutting a pinion or wheel blank B rotatable on its axis 69 by gearing 71, 73, 75, 76, &c. The blank is carried in a member 63 vertically adjustable upon the framing 64 and is inclined out of the plane of the paper, its axis 69 being directed to a calculated point 66 in the vertical plane in which move the two planing-tools 30, 31, themselves moving towards the axis 67 of a carrier 60 in which they are mounted. The carrier is rotated in a vertical plane by gearing 72, 79, the blank and tools rotating at speeds corresponding to those of the blank and basic crown wheel gearing together. Two tooth sides are cut simultaneously before indexing. In a. modified use of the apparatus, the blank and tools are, continuously rotated for continuous indexing, in which case curved teeth are produced. The basic crown wheel may have curved teeth, if the tooth inclination angles of the gears conjugate thereto will fulfil the terms cf the first-mentioned equation. The teeth of the basic crown wheel may be of curved profile, in which case different pairs of tools are used on the gear and pinion. The profiles of the gear teeth are of different curvature on opposite sides, and to ensure correct cutting the profiles of greater curvature may be made of increased pressure angle. Specifications- 199,462, 263,798, and 270,669 also are referred to. According to the Specification as open to inspection under Sect. 91 (3) (a) the pinion and wheel may be generated from different basic crown wheels, at least one of which has non- radial teeth. The wheel may be cut as an ordinary bevel gear with straight radial teeth,. the axis of the blank not being offset from that of the generating basic crown wheel, the pinion being generated from an offset basic crown wheel and having its two tooth sides cut in separate operations. This subject-matter does not appear in the Specification as accepted.