GB310240A - Improvements in methods of milling screw threads - Google Patents

Abstract

310,240. McLeod, R. J. July 18, 1928. Milling screws. - In a machine for milling screw-threads by means of hobs having the same pitch as the work, a differential gearing is provided for varying the relative speeds of the hob and work to avoid the formation of facets, means being also provided for giving compensating relative axial traverse to the hob. A gear box 11 which may be coupled to a motor at 12 imparts a four-speed and reverse drive to a shaft 21 which is connected through further reversing gearing 18 to drive a spindle 3 carrying the work 1. The shaft 21 is connected through differential gearing 22, bevel gearing 23 and worm gearing 24 to the hob spindle 6. When cutting a screw to depth the differential gearing runs idle but for multiplying the number of facets formed in this operation the rotation of the hob is modified by imparting to it an additional rotation. For this purpose the spindle 21 is connected through gears 27, reversing bevel gearing 26, bevel gearing 28, change speed gears 29 and worm gearing 31 to the casing of the differential. Corresponding axial movement is imparted to the hob from the gearing 26 through a shaft 32, gears 33, change gears 35, worm gearing 37 and lead screw 38 operating the hob saddle 9. The hob may be fed to depth by means of a screw 39 and a former plate 40 may be used for screwing taper threads. The reverse gear 17 enables the whole machine to be reversed to take a fresh cut while maintaining the exact relative positions of the threads on the hob and work. The change gear 13 - - 16 enables the return movement of the hob and the finishing cuts to be effected at high speed.