Re: [CAD_CAM_EDM_DRO] Building A Cheap DRO

Has anyone tried photographic methods to put lots of
black lines around the circumference of a plastic disk
to make an optical encoder? How are long linear encoders
made?

Raymond Heckert wrote:

>
> I'd be greatly concerned about the amount of tension you need to have in
> the wire that's wrapped around the encoder shaft. Most rotary encoders are
> designed to handle only very light "side-loads". Also, even at 1 inch of
> wire wrapped per rev, how many turns of wire can you even put on the
> shaft?? You probably only get 20" of travel, max. And don't forget about
> the "sweep-angle" error that would be induced. Also what keeps the wire
> from "piling up" as the sweep angle gets greater. I'd worry more about
> these things than the dia of the "pulley" (shaft), or the uniformity of the
> wire dia. There must be better ways of doing this ...for what it's worth.
>
> RayHex
>
> ----------
> > From: cutsgems <chuknospam@...>
>
> > I'd like to add a 3 axis DRO to my mini-mill. I've investigated the
> > Calareo/Wholesale tool import digital machine scales & readout box,
> > nearly $500 to cover all three axis. So what I had in mind was some
> > encoders from US Digital, something like 2000 PPR?? to get 0.0005"
> > resolution, use a simple wire under tension wrapped around the axle of
> > the encoder to convert the linear motion to rotary. Use an old laptop
> > & printer port & available software for the readout.
> >
> > My questions are the mechanics for the encoder.
> > Would a 1000 PPR encoder give me the resolution required if I used
> > 0.6369" diameter hub on the encoder as opposed to a .3183 diameter hub
> > which would only yeild a .001" resolution. Or am I better off using a
> > 2000 PPR encoder with the .3183 hub? (The .3183 is a rough calculation
> > required to convert 1" of travel into 1 rev on the encoder).
> >
> > Secondly, when calculating the hub diameter, how do I account for the
> > wire diameter in the calculation? Is it 1/2 the wire diameter +/- the
> > hub diameter???? Thanks.