A Study of Effects of Geometric Form Variations to Diametric Differential of Threads

Abstract The effects of geometric form variations on a difference of functional diameter and pitch diameter of manufactured threads are studied. The difference is defined as a diametric differential. The four types of errors, flank angle, pitch, circularity, and taper are individually investigated for the effects on the diametric differential. Inherent relationships and behaviors of the errors are explored. Calculation methods of individual effects and a combined effect are discussed and developed. This research found the form errors of a thread part deviate its functional diameter from its pitch diameter towards the maximum material size; the form errors can significantly impact on the diametric differential so that their effects can easily cause functional dimeter (FD) and pitch diameter PD out of a pitch diameter tolerance; pitch variations within tolerance can make a pitch diameter easily out of tolerance in their conformance assessment; a total diametric differential by all the form errors is approximately an arithmetic sum of the individual diametric differentials.