GB315063A - Improvements in method of generating helical gears - Google Patents

Abstract

315,063. Trbojevich, N. May 29, 1928. Gear-cutting.-Helical involute gears and like twisted surfaces are generated by means of a pair of plane disc cutting or grinding tools mounted on the same arbor and having their operative faces located and maintained in tangent planes drawn to two different tooth surfaces of the blank. An involute helical surface, Fig. 1, is generated by tangents t to a base helix h, these tangents intersecting a plane xy perpendicular to the helix in an involute d drawn from the projection circle co of the helix. Thus such a surface may be generated, as described in Specification 160,832 by a cutter J. Fig. 3, containing a generator t of the helical tooth surface. According to the invention it is shown that a pair of parallel cutters J1, J2 representing two tangent planes may be set so as to straddle a number of teeth of a helical gear G and to generate two different tooth surfaces simultaneously. If -y, is equal to the base helix angle then, denoting the distance A1, A2 representing the intercept of a tangent to the base circle co between involutes d1, and d2 by x1, it is seen that x1 = arc o1, o2 = aw. Also if x2 represents the distance between the generating planes then x2 = x1 cos gamma0 = aw cos gamma0. If # represents the transverse pressure angle of the gear blank then w may be found from the equations The distance x2 between the operative cutter surfaces is thus exactly determined and during operation in a milling machine the blank is rotated and fed axially to produce the required helical lead. After each cut the cutters are returned, the blank indexed and the process repeated until all the teeth are generated.