Peter L. Peres wrote:

> I once built a very good and safe coil winding machine from a scrapped
> dot-matrix printer stepper motor, that could be revived as a PIC
> project imho.

  Yeahh.  Love the idea.  Something useful to do with one of *all* those
steppers I have this compulsive urge to collect.

> Hmm. Assuming 1E6 life,

  I kind of thought (vacuum) reed switches had a life expectancy *much*
greater than this.

> Also, I suppose that the user would go on hearing click-click
> click-click in his head for a long time after stopping the unit.

  More like "tink-tink".  I know what my telephone exchange is doing
when I'm sitting in the office, though my secretaries don't seem to make
the same connections(!).

> 1. Lathes are NOT coil-winding machines, unless the shaft can be
> equipped with a torque limiter.

  Quite so.  This has proven a major limitation in the past, and the
stepper motor idea will amuse my father (chief coil-winder) no end!

> 2. Optical sensors are used a lot in lathes, both reflective and
> transmissive, but only in locations where they are encapsulated and
> protected from debris.

  Thus my comment to the effect; not for the amateur/ cheap job.  I have
however picked up some Logitech trackball assemblies from a local
disposals source.  The difference in the mechanics to a "cheapie" is
impressive.

  They contain three bearing points for the ball which appear to be
(synthetic) jewels (but could just be ceramic/ glass), and a
cantilever/ spring assembly to hold the "followers" against the ball.
The follower is a roller of fairly stiff foam which might wear if used
against an uneven surface, but has tremendous grip and shouldn't be put
off by dust.  I could envisage "hacking" this mechanism to follow a
slow, dry, smooth shaft quite well.  But not precision.

>  This could be a PIC project too. A PIC and a ULN 2803 would be all
> that's needed. And it's MUCH safer than a misused electric drill or
> lathe.

  Hmmm.  I'm thinking, along with the multiplexed seven-segment display,
it would automate really well.  No point using a PIC if it doesn't do
all the precision counting!  I can visualise a joystick or lever
forward/ backward control ("jog shuttle").

> hope this helps, and sorry for the long posting,

  Naah, for you, Peter, it was brief!
--
  Cheers,
        Paul B.