The Measurement Of Involute Worm Wheels

Abstract

This paper describes the traditional methods used for checking worm gears, using contact marking techniques and discusses a new method for the analytical measurement of worm gears which uses a CNC gear inspection machine at the UK National Gear Metrology laboratory. Some of the development and validation problems are discussed and example measurement results are given. 1.0 Introduction and Background Equipment, standards and procedures for the measuring of involute spur and helical gears have been available for many years. During this time, manufacturers of involute worm gears, although an important part of the transmission business, have not had this luxury because the geometry of involute worm gears is far more complex than involute spur and helical gears. A typical worm gear pair is shown in Fig. 1. The development of analytical inspection techniques could not be implemented until CMMs or CNC machines, with sufficiently powerful computers became available. 1.1 Conventional Contact Marking Inspection Procedure The involute worm is an accurate screw thread with an involute profile and it is relatively simple to measure. Standard gear inspection machines or CNC gear checking machines may be used with acceptable accuracy. The worm wheel is far more complex. It is not feasible to build a mechanical inspection machine for checking worm wheels. Worm wheel manufacturers have traditionally used a contact marking test procedure, as outlined below: Transactions on Engineering Sciences vol 16, © 1997 WIT Press, www.witpress.com, ISSN 1743-3533