GB452239A - Improvements in and relating to generating hobs - Google Patents

Abstract

452,239. Hobbing splines. BURGESS, A. F., 10, New Court, Lincoln's Inn, London.- (Barber-Colman Co. ; River Street, Rockford, Illinois, U.S.A.) Aug. 23, 1935, No. 23695. [Class 83 (iii)] A generating hob 10 for cutting the keys 13 of a shaft 11 for securing an outer member such as a gear hub has a helical thread consisting of a series of successive finishing teeth of uniformly varying width at the pitch line, the opposite faces of the teeth having different constant lead angles. The spaces between the keys have roots b, Fig. 4, which lie on a cylinder and are thus of constant depth while the sides c d bounding these spaces taper inwardly from the shaft end and form helicoidal surfaces. Clearance slots 15 are preferably formed along the sides of the roots b. The hob is preferably single threaded and has longitudinal gashes 20 to form teeth 21 which are backed off spirally in the usual way. For generating straight sided splines, the sides f, g, of the teeth are of involute form. The thread 18 has uniform lead but opposite sides of the thread have different leads according to the form of splines to be generated. Thus the two sides c, d of the splines are generated on different pitch circles, Fig. 2, i, j, showing the pitch circles and ii, jj, the corresponding pitch cylinders of the two sides of the hob thread. The mean longitudinal pitch of the hob thread is found by dividing the pitch circle at the outer end of the work by the number of keys 13. The difference in lead of opposite sides of the hob thread is then calculated from the difference in widths of the keys at opposite ends and the number of convolutions of the hob, the two sides of the thread preferably having leads equal to the mean lead plus and minus, respectively half the above difference. Spaced clearance lugs 22 produce the grooves 15. In one form, Fig. 2, the teeth are of uniform height but in a modification the hob is uniformly tapered externally so that the teeth are of decreasing height. In operation the hob 10 is positioned as shown in Fig. 3 with the wide end of the teeth leading and the operative teeth lying along the grooves to be cut. During the timed rotation of hob and work the hob is fed in the direction k to the dotted line position, the component n being preferably a constant speed and the component o adjustable to give the required resultant. Specification 454,291 is referred to.