Bob,
I finally got a response from the HobbyStore.
This is so far the best concept of a worm gear I have found. (out of about 30-40 designs)
It's the cheapest version of a metal worm gear set that I could find, that is relatively sized to suit the scope.
The gear is around $200 inc gst and the worm is around $60 I think.
My ideal price range for the set would be around $100-$150, but the gear set went up about 25-30% after June 30th.
(and they call this a recession where prices should come down somewhat???)
The other ones I have found, were cheap and plastic (...pffft)
But I suppose I can't complain, as I haven't yet hit the costs on astrophotograhy........Many thousands to go....Hahaha.
Oh the joys (and expense) of a hobby.
For what it's worth:
This gear's diameter is about 150mm and a has 360 teeth.
http://farm3.static.flickr.com/2443/...ea316f4c_b.jpg
http://farm3.static.flickr.com/2586/...52492a79_b.jpg
EDIT:
I'd love to make one, I have the tools at work, but I don't think I'll have the permission to use them.
Which is the reason I have gone down the road of "purchase".