GB767507A - Improvements relating to methods of and machines for forming screw threads on fastening elements - Google Patents

Abstract

767,507. Screwing. WINWOOD, D. G. A., and MASON, R. V. Dec. 21, 1954 [Sept. 23, 1953; Nov. 25, 1953], Nos. 26171/53 and 32655/53. Class 83 (3). A machine for screw-threading the pointed or " gimlet " end 18 of a screw 16 comprises a holder for a screw-blank, a first tool-holder 24 to support a thread-cutting tool 23 for cutting a parallel or slightly tapered thread on the screw shank or to support a nut-member for engaging a thread on the shank, a second tool-holder 30 to support a tool 31 for cutting the thread on the pointed end, and means 37, 38 for moving the second holder towards the axis of the blank. The tool-holder assembly is held in a tailstock 12 and can be moved angularly by a handle 29 within limits determined by a stop 46, not only to close the tool-holders 23 towards the work against spring-pressure by an amount determined by cam-slots 28, but also to move the rollers 37 into the path of the cams 38. If the shank of the screw-blank is unthreaded, the dies 23 cut the thread thereon as the tailstock is traversed away from the screw-head, by a lead-screw rotated in correct ratio to the rotation of the blank. At the end of the traverse the rollers 37 engage the cams 38 and are moved in a straight or curved tapered path to thread the pointed end. If the shank of the screw is slightly tapered, a longitudinal camslot on the machine bed rotates the member formed with the cam-slots 28 to produce the taper. Alternatively, a set of rollers and cams such as 37, 38 is provided for this purpose. If the shank is already threaded, the dies 23 are replaced by nut-members to provide an automatic feed when the blank is rotated. If the screw-blank is not initially tapered at its end, the thread is cut thereon in a series of steps by arranging for an incremental radial in-feed of the cams 38.