Re: [CAD_CAM_EDM_DRO] Timing Belts and Pulleys

I have worked with many machine tools that had very heavy tables and running
on timing belt and pulley's there is very little problem as long as the
frame that the motor mount is stiff enough. If all the ratios come out even
there shouldn't be any need for linear calibration. There are also side
benefits to the belts there will be a better finish on the parts compared to
direct drive.

Harko

On 11/17/06, Frank <ftkalcevic@...> wrote:
>
> I posted this in the DIY-CNC group and it was suggested this might
> be a better group to ask....
>
> I'm still in the process of cobbling together my gantry CNC mill. It
> is made up of mainly linear actuator assemblies gathered on ebay.
> They are all currently powered by servos directly connected to the
> ballscrews of the actuators.
>
> Seeing there is no way I'm going to be running the motors at speed
> to get the rated torque, I want to gear them down using timing belts
> and pulleys. I went to the www.sdp-si.com site and used their
> calculator. It came up with 50 tooth pulley and a 25 tooth pulley, a
> belt spaced 60.21mm apart.
>
> My questions...
>
> 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?
>
> 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?
>
> 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.
>
> 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?
>
> Thanks,
> Frank
>
>
>


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