Re: How to establish repeatable home position w/steppers?

--- .000125 resolution is just the relationship between a leadscrew
and the step angle and how slow you are prepared to accept your
equipment. A direct drive from the shaft will still be as repeatable,
just with larger steps. A fine leadscrew does not make for more
accuracy, just smaller steps.
.000125 repeatability is difficult with expensive machine tools and
is
pretty impossible for home built crap.
Most use the the nc concept for making multiple parts that are
identical and the programmes can be adjusted if the fist piece does
not measure correctly. This is a lot easier than trying to adjust
discrepancies out.
Terry Ackland

In CAD_CAM_EDM_DRO@egroups.com, dougrasmussen@c... wrote:

> Dave,
>
> .0002" is getting into the ballpark. .000125" is my theoretical
> resolution so that's what I'm shooting for.
>
> Maybe some sort of encoder device on the motor shaft would be the

way

> to go?
>
> thanks,
>
> Doug
>
>
>
>
> --- In CAD_CAM_EDM_DRO@egroups.com, dave engvall <dengvall@n...>
> wrote:
> >
> >
> > There has been some discussion of limit switchs/home on the list

in

> the last month or so. One person was getting a thou or so out
> > of micro-switches ( he did not state his limit of resolution) and

I

> get 0.0002"repeatibiliity from hall effect devices. They might
> > be better than that but that is my resolution limit. :-)
> >
> >
> > Dave
> >
> > dougrasmussen@c... wrote:
> >
> >
> > > Group,
> > >
> > > On an open loop stepper system how do you establish a

repeatable

> home
> > > position? I'm thinking of a home position that will repeat to
> within
> > > the resolution of the machine.
> > >
> > > I can't see that normal, every day limit switches will do the

job.

> > > Dial indicators would be a pain, but would work provided they
> didn't
> > > get bumped or readjusted. Some very old machines used a

vernier

> dial
> > > which was manually stepped to position.
> > >
> > > So, what method are most of you using?
> > >
> > > thanks,
> > >
> > > Doug
> > >
> > >
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