Re: [CAD_CAM_EDM_DRO] A/B (anti-backlash) rack/pinion drive was Re: tensioned ballscrew

----- Original Message -----
From: ballendo <ballendo@...>

> Doug,
>
> Most routers using rack/pinion just use a spring to "load" the pinion
> toward the rack.

I presume they use a special pinion with an enlarged tooth profile to get
zero clearance without over-engagement of the pitch line..

>
> At lower levels of preload, a split gear is used, with springs.

Or for higher preload the split gears can be bolted together and adjustable
to accomplish zero clearance per my above comment.

>
> You could also "skew" the pinion axis in relation to the rack to
> create anti-backlash. You'll create uneven wear, but it is a simple
> approach. a spring could provide a constant (and adjustable) source
> of "skew-ing" pressure.

Yup. Uneven wear, and point contact instead of line contact at the pitch
line. The split gear approach would likely be easier to implement anyway.

>
> Be sure to calc the tooth loads if you decide to use rack/pinion
> drive, whether preloaded or not. And as I've mentioned before, you
> will have less backlash due to center distance variations with the
> older 14-1/2 degree Pressure angle, at the expense of some tooth
> strength, compared to the modern 20 degree PA.

Agreed. I am looking exclusively at 14.5 degree PA.


>
> Just thinking here out loud: If you used a wider rack (to allow 1/2
> tooth to carry the necessary load) you could fabricate a "torsion-
> based" pinion of smaller diameter than the A/B "split" gears commonly
> available.

Here's another thought. Use two pinions in tandem and tie them together
with a double sided timing belt. Drive them with a third timing pulley on
the outside belt teeth. Preload between the pinions would be adjustable
using the third pulley and an idler on the opposite side. This gets around
the double tooth loads associated with a split gear - at the expense of more
complexity. It's still simpler than rotating nuts or moving screw supports.

Doug