Re: [CAD_CAM_EDM_DRO] Timing Belts and Pulleys

Hi Frank,

> 1) With a 50 and 25 tooth pulley, will this give me an exact 2:1
> ratio or will there be an error factor? Will I need to calibrate my
> mill by counting steps and measuring the distance?
>

You will get exactly 2:1.

> 2) Can I place the pulleys at the specified distance, 60.21mm? Or do
> I need to add some to allow for belt tensioning? In this case would
> I be better off making one side adjustable? I will probably use two
> stages to give me 4:1, so do I need to make the middle pulleys
> adjustable?
>
>

Allow for adjustment. Toothed belts need a fair amount of tension to
work well. Even if the spacing is exactly 60.21 you would never be able
to fit the belt. If you need 4:1 why not do that in one go. If you can't
get exactly 4:1 it doesn't matter. You just tell your controller exactly
how many steps/unit you get and it will work the rest out.

> 3) What is backlash like with timing belt pulleys? I've read some
> other posts, and it seems the elliptical tooth profile is a good
> choice.
>

In practice this is negligible. If you are paranoid about backlash,
larger pulleys have less effective backlash than smaller pulleys. If you
are using pilot bore pulleys, bore them in a lathe rather than drilling
them using the pilot. You want the pulleys running dead nuts true or you
will get cyclic errors.

> 4) How will timing belts effect the required servo stiffness? I
> currently have the gain quite high to get a rigid feel (still
> haven't milled anything though). Do the timing belts allow for a
> softer (and hence quieter) gain ie will the stiffness be multiplied
> like the torgue? Or, do the timing belts add a springiness to the
> drive?
>

The stiffness will increase with the ratio. If you use 2:1 then the
stiffness will double. A properly sized and tensioned belt will have
very little give.

Les