Re: [CAD_CAM_EDM_DRO] rack&pinion

Peter,
there are a few ways to get rid of the backlash of a
toothed bar and pinion construction.
first you can mount two toothed bars little displaced to the second
or as I have seen in one occasion the second smaller one had e spring
load against the first.
second which i saw more often is a parted pinion where one half is
pressed with some springs away from the other and had a kind of end
stop so it wouldn't displace too much.
In both cases there is the inconvenience that even if you have
perfect envolvent curves the machine always will make jumps.
Like when you have a chain drive with small sprockets the polygon
effect makes that the chain gets tensioned end loose.
The rack and pinion construction will have a speed oscillation which
becomes worse as smaller the the pinion is.

To get a perfect movement you would have to vary the speed according
to the displacement speed. (I guess it wouldn't be to good for the
driver and motor.)
Or to get a perfect positioning you will need a linear encoder.

I would recommend this construction for long movements without
high precision in speed and positioning. Like for example
in the x movement in a surface grinder. and there you will not have to
take out the backlash.
Or a wood working machine.

Best wishes to Malaysia
Sven Peter

cadcamcenter@... wrote:

> Hi,
>
> Excuse me for going in a different direction as everyone here seem to
> be fixed on ball-screw or its poorer cousin the lead-screw, and would
> thumb their nose at rack-and-pinion, but.....
>
> Questions:
>
> Why? Is it because of higher backlash? If so, any qualitative
> indication? Any redeeming factors? (like higher speed, easier
> construction, lower cost?)
>
> How would one keep the "pinion" on the "rack"? Any link to a site for
> more information, especially diagram?
>
> Thanks
>
> Peter
>
> Addresses:

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