Re: [CAD_CAM_EDM_DRO] Updated DRO using screw threads not pulleys

Ian Wright wrote Fri, 7 Jul 2000:

> I have been considering a similar set up to yours for a DRO but I was going
> to use another pulley outboard of the encoder as well. By doing this you can
> take a complete turn around the encoder shaft (yes, I know it will screw but
> I thought that the shaft would probably be polished enough for the line to
> maintain a reasonable position) and it also takes all the strain off the
> encoder shaft.

How about this improvement? What we'd like is to do is wrap the wire
several times around the encoder shaft to:
- increase holding friction (so the wire doesn't slip)
- take bending strain off the shaft (so the encoder shaft is in the middle,
not the end), and say the wire comes from left, around the shaft a few times,
and unspools right.

We can't do this with a bare shaft, because the wire wants to 'walk' down
the shaft and wear by rubbing against itself. Also presumably there are pulleys
at the ends which don't walk, causing misalignments.

Answer:

Instead of using pulleys and bare encoder shafts, substitute screw threads
everywhere. The wire sits in the grooves of the screw threads.

In the center is an encoder shaft with screw threads, so the wire
(for encoder or even direct power drive) winds around the screw threads numerous
times, and also at the ends, the wire "walks" down the screw threads at the
same rate! Everything stays in alignment.

Doug Fortune