Thanks for the info Bojan. those are good articles.
friction drive is an attractive option, but maintaining pressure on the rollers and concentricity of the rollers would be key factors.
if i can fabricate an assembly that can adjust pressure on the rollers, it might be practical.
my existing stepper has got a 20 tooth T2 timing pulley.
i also have a 130 tooth timing pulley.
so the first stage would give a ratio of 6.5:1
if I get a 100:1 reduction with a worm/worm wheel stage, i should get a reduction of 650:1 which is ample.
will also look at driving the worm directly with the motor with low freq pulses and a high torque motor.
I was reading up on worm parameters, apparently lower pressure angle yields lower noise but lower power transfer. 20 degree is the industry norm.
also lead angle.
smallparts actually have a pretty extensive collection. this is why i started this thread as I wasnt sure of what to choose.
http://www.smallparts.com.au/store/categories/worms/
I found these options close to what i could use. only issue is that with a quadruple start, I think the ratio is teeth/4.
what is the significance of number of starts, does it affect efficiency?
100 tooth quadruple start
http://www.smallparts.com.au/store/i...ries5metallic/
100 tooth antibacklash worm wheel
http://www.smallparts.com.au/store/i...ries5metallic/
single start 120 tooth
http://www.smallparts.com.au/store/i...ries2metallic/