Re: [CAD_CAM_EDM_DRO] Building A Cheap DRO

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.