Re: bench top DRO

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ebiz_59" <chuckm@3...> wrote:

>
> I'm looking for a cheap implementation for a 2 axis DRO on a benchtop
> mill - about 30" by 15 travel. Looks like I can get some free
> software to read encoders from Steve Lindsay
> http://www.lindsayengraving.com/other_interests/dro.html
> I'm wondering about buying linear scales and using them for the
> encoders , I should be able to make them work, don't you think? And
> anyone who has a source for linear scales or appropriate rotary
> encoders who could point me would be greatly appreciated. Chuck
>

For "cheap" you almost have to implement some form of rotary encoder.
First check out the "low cost" solution of at Sumatech forum. They
have a solution for the cheap chinese scales.

If you were to get the backlash down on your mill (look for group
threads on building zero backlash nuts on this list) and mount some
rotary encoders (best deal for new ones is US Digital encoders) then
you can download the MACH3 demo and hook up the encoders to parallel
port pins and readout position with that. Once you have that then the
addtion of motors gets you close to having a full CNC conversion! As
long as you don't run over a thousand lines of g-code with MACH3 then
its free to play with. There are some interesting threads over at
MACH1MACH2CNC (home of the MACH group) of using steppers in an open
loop control but taking the feedback from encoders and performing a
safety stop if postion is lost.

The key to doing any of this is to get your leadscrew backlash to as
close to zero as possible. While ballscrews will do that, there are
some lower cost (but more labor intensive) options.