Application of interferometry to the measurement of the pitch of threads on a lead screw.

A rapid, interferometric method for measuring the pitch of a nonrotating lead screw that involves no mechanical contact with the thread is described. The moving plane mirror of a Michelson interferometer is set on the axis of the lead screw. The lead screw is mounted on the carriage of a machine which moves it parallel to its axis. The Michelson fringes are counted continuously as the screw threads are moved across a light beam. The Michelson interferometer uses the green line of a (198)Hg isotope electrodeless lamp. The passage of a pitch point, to punctuate the fringe count, is sensed by photoelectric microscopes, and associated electronic circuitry, as described herein. The performance of the apparatus is presented.