GEAR HOBBING WITHOUT CHANGE GEARS

摘要

It all started way back in the early 1990's while watching the Norton Racing Team at Cadwell Park on their Wankel powered machines, I decided to have a go at making a Wankel engine. After many trials and tribulations I successfully made two, a single and a twin chambered. Both ran but were difficult to control, so I decided to make a half size Norton engine. I needed some means of accurately cutting the internal gear teeth on the rotors and the fixed gear pinions. The gear size to be used was 32DP which is also the same DP as the gear train on my lathe. Two gears were bought from "Hinchcliffe Gears" which enabled me to make a 32DP hob using the method described by Dr Giles Parks in M.E.W. No. 57 - April 1999 (photo 1). To be able to hob gears it is necessary to synchronise the gear blank to the hob. As in screw-cutting, it is normally achieved mechanically by a gear train. To cut different numbers of teeth the gear train has to be altered, hence, as with a lathe, you need a good stock of change wheels. If instead of a gear train a stepper motor was used to synchronously rotate the gear blank, life would be easier.