Worm gear?

Does anyone know where to buy a worm gear and wheel - come to think of it, does anyone know what the parts are called? Is the spiral thing the worm, and the gear thing the pinion? Or what?
Anyway, looking for something say 30-50 mm gear diameter, 40-90 ratio. Sort of thing you might use in a 2" rotary table.
Ta,
-- Peter Fairbrother

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HPC do worms and worm wheels:- http://www.hpcgears.com/
http://www.hpcgears.com/newpdf/worm_wheels_0.5mod.pdf
You might not like the prices but they're probably not outrageous. You can play with the options to try to get a cheaper solution.
Alternatively, you could go down the route of free-hobbing a worm wheel using a home made hob or even a tap as a crude hob. Might not be acceptable for a rotary table, but you never know. You could compromise by using Meccano gears and worms. The gears were cut with 40DP cutters, but the pitch and tooth form or the worms and racks are actually that of 9/16"BSW, so you could hob a custom worm wheel with a tap and expect it to work.
Mark Rand RTFM

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College Engineering list 40:1, 60:1 and 90:1 in their on line catalogue.

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Hi If you let me know exactly what you want ie ratio diameters dp etc, I can hob the pair for you and I will be cheaper tjan HPC and College. Peter