On Wed, 2 Feb 2011 14:14:09 +0200, you wrote:
>When belts are tightened well, then I think it is good from backlash
>point of view. The main question, just like Gene pointed, is designing
>it to be compact, not a large and bulky box.
>30:1 ratio might require even more than 2 stages - one would need to
>combine 6:1 and 5:1 ratios to get it in 2 stages, but that involves
>very high differences in pulley sizes, so for compact design only very
>few teeth will be in contact on small pulley.
>But in the mill head the belt will have to deal all the forces between
>endmill bit and material, that is why I think that just several teeth
>in contact between belt and pulley might lead to short lifetime of the
>belt.
A 10 tooth 5mm pitch belt is only 15mm diameter
A 60 tooth 5mm pitch belt is 95mm diameter
There are no dimensions on the Doughty page for the bigger drive, but
I'd guess it's a bit wider than 100mm.
As for thickness, using 9mm wide belts, you'd get 2 in something 20mm
thick, (without covers) but that would only get you back to the same end
as the drive.
Now you could get three 6mm wide belts in there and use larger pulleys
for more teeth in :)
I reckon you could do it in something of a similar size of that drive.
Tooth shear strength exceeds the overall belt strength if Gates are to
be believed. They rate HTD belts max power transmission of a 5mm pitch
HTD belt as 12.3HP per inch of width, so the 6mm belts are good for
1/2HP or so, how that equates to the 20 ft pounds holding force Doughty
claim, I'm not sure.
Steve Blackmore
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