Re: Building A Cheap DRO

I built the inferface for this DRO about a year ago and played with it
using some of the Surplus Center encoders that were available at that
time. It works great, and I am currently building the encoder mounts
as designed by Bubba to put a DRO on my 7x12 lathe and my small mill.
With a little scrounging, I really think you could build a 3 axis DRO
for cheap, like $100 or less. The biggest expense will be the
encoders but I am sure they can be found on ebay or at the various
surplus houses for low $. Any old PC wil run the DOS software for
this DRO and your will have all the accuracy you could ask for,
probably more than your machine is capable of.

The encoders I used / will use are 1000 line encoders, which in
quadrature is 4000 lines or .00025 per line. If you use any type of
mechanical advantage system on Bubba's DRO design you could be looking
at .000125 resolution which I doubt most machines can achieve or
maintain.

Thanks for your design Art, your work is greatly appreciated.

John Guenther
Sterling, Virginia

-- In CAD_CAM_EDM_DRO@y..., Art Eckstein <axtein@d...> wrote:

> I "was" worried about the tension issue until I designed the

housings that

> I used that include ball bearings. Not only will this allow greater
> tension, it lowers the friction required to turn the shaft.
>
> I thought about using the multi-turn idea but quickly discarded it

for the

> very reasons you mentioned. The result was to build the system to

maximize

> the amount of cable around the shaft (and keep a simple design) so

the

> contact angle is 180 degrees. I am always trying to think of better

ways

> and one that I recently thought of was to add a pressure roller

(again with

> a ball bearing) similar to what is done on a tape recorder capstan.

This

> should increase the pressure on the encoder axle without increasing

the

> cable tension further. However, right now there are other projects

on my

> plate and the darn thing works as is!
>
> At 09:42 PM 3/18/02 -0800, you 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
> >
>
> Bubba
>
> OLDER THAN DIRT
> Country Bubba
> (Actually the inventor of Country and Bubba)
>
> axtein@d...
> LaGrange, GA
>
> http://members.dicomm.net/~axtein
>
>
> [Non-text portions of this message have been removed]