Re: Cheapie import DRO scales for a Mill/Drill Quill?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, shyningnight@y... wrote:

> I've been contemplating upgrades to my Enco (Late 80's mfg, round

column) Mill/Drill...

> I plan to add CNC to the X and Y, and later to the Z.. the Z is

going to take a lot of work on

> the quill feed or building a new Z drive system...
>
> Anyway... that's not the point of my post.. (damn antihistamines

for allergies keep me

> from thinking a straight line...).
>
> I happened to spot some "cheapie" DRO scales on eBay in the $25 to

$35 range, for a 4" or

> 6".
> I was wondering if anyone had any experience with these glorified

calipers with delusions

> of grandeur on a Mill/Drill Quill?
>
> In the short term, just as a "dumb" DRO...
> And MAYBE, in the long term, could one be interfaced with a

computer (paralell port) as

> part of a CNC retrofit?
>
> I'd appreciate anyone experience or views on 'em!
> Paul F.

Two quick things here: Check out the yahoo group Shumatech. They
are using the cheap scales and external electronics to make DRO's.


If your intent it to use the scales as feedback for a closed loop CNC
control then you will be faced with the challenge that there can be
little if any slop in the mechanicals. If you measure the table
position and have any backlash in the mechanics (motor, leadscrew,
etc) then the loop gain will have to be cranked so low that accuracy
will suffer or the system will oscillate violently. If you use zero-
backlash ballscrews to take out the backlash (recommended) then you
might as well put rotary encoders on the motors.

I don't know if the external electronics output the quadrature
signals you will need to match up to the possible CNC solutions. I
do know that the output from the scales is NOT quadrature and will
not interface directly with standard hobby type CNC equipment.