Thanks everyone for the great spread of replies, liked Neil's interesting variation on the theme.
Yes, John Stevenson was a very prolific contributor to engineering topics but particularly because he seldom re-gurgitated old ideas, nearly new and original every time. I was well aware of his contribution to the topic before I placed my post but for all who are interested you can peruse these links:-
http://bbs.homeshopmachinist.net/threads/42051-A-form-tool-for-gearcutting
….and-
https://metalwebnews.com/howto/gear/gear1.html
Thanks again.
By the way, I suspect that most of you posters are in the UK (I'm in New Zealand). I can't resist relating an amusing anecdote to you. Some of you may well know that New Zealand has a mini cottage industry re-building de Havilland Mosquitoes (the production form-tooling/jigs are amazing, by the way). Having witnessed the first public display flight of the first-build I was mightily impressed…..
….. so there I was just about to walk into the local supermarket in Papakura last Wednesday when, what should I hear, but the familiar sound of two roaring R-R Merlins overhead? Yes, it was the latest new-build dH-M doing test-flights. A great sight and as I craned my head skyward I muttered to the guy standing next to me, words to the effect "I bet that'll frighten a few Germans!"
He said something like "Hmmm, Interesting" – but in a thick, German accent and "No", he wasn't having a joke with me!
"Ooops!"