Design Method for Profile of Screw Rotor Hob in Consideration of Interference. 1st Report. Method to Obtain Profile of Basic Thread Surface for Hob which cuts a Given Screw Rotor Surface.

Abstract

A precise analysis has been made for a design method in order to obtain the profile of a basic thread surface of a hob which cuts a given screw rotor surface, especially in the case in which a screw thread profile is given as a series of dispersive points. Firstly, it is clarified that under certain circumstances a singular point (a cusp) will occur on the basic thread profile of the hob corresponding to the screw rotor profile, and that, because of the cusp, the interference phenomenon will occur on the basic thread surface of the hob. Secondly, numerical analyses are proposed to determine the interference by using a conditional equation of the cusp as well as to obtain the basic thread surface of the hob. Then, these analyses are theoretically verified by applying them to the dimensions of a pair of screw rotors.