Screw thread formation on tapered work - has angle of feed of screw cutting tool altered to compensate for change in helix due to taper

摘要

The method is for formation of a screw thread of constant pitch on a frusto conical workpiece by relative rotation of the workpiece (17) and thread-forming tool (24) so that the conical surface of the workpiece is held firm. The thread-forming tool (24) is moved axially w.r.t. the workpiece. The tool is simultaneously moved radially to the workpiece. The angle deviation, defined between a first plane normal to the axis of rotation of the rotating tool (24) and a second plane normal to the rotary axis of the workpiece, is also simultaneously altered. This causes the first plane on the rotary axis of the tool to be cut so that the required direction is adopted in order to produce a geometrically correct conical thread, to compensate for the increased helix angle at the narrow end of the work.