Re: [CAD_CAM_EDM_DRO] Relation of a DRO to a CNC modification of a machine?

Gary;

As the fellow owner of a CNC'd 3in1 machine, I feel it my duty to pipe
up. <G>

If your DRO is the type that uses the standard Chinese "legless
caliper" type of scale, no, your DRO cannot be connected to the CNC
system.

As such, it is only useful when manually machining. Having said this,
I do a lot of manual machining, so don't feel that you may have
purchased something you won't be using. As cool as watching a CNC
operation is, it's still kinda neat to do it by hand.

Also, there are a number of operations where I use CNC to get it close
to the right size, particularly when there is a lot of material to
remove, then manually (using the DRO) to get it closer still, then
manually using traditional measuring tools for the last few cuts.

The issue is that there is enough play in my (and I suspect most) 3in1
machine that .010" is about as close as I'm willing to believe the
CNC can get something to (and I've upgraded mine with good-quality
ballscrews and double-nuts).

And there's enough stiction and flex in my "caliper" style DRO that I
don't believe it to be repeatable to within .002", so anything closer
than that gets mic'd.

However, if your DRO is a more standard type, where the output of the
encoders is conventional quadrature, then there IS a way use the
feedback from the DRO to the CNC system to "compensate". You'll need
(beside the DRO)

a. a "Kulaga/Mauch" DRO input board
b. a PC with an ISA connector to accept the above board, and
c. either EMC or DeskNcRT software (there may be others I'm unaware
of)

(I'm building exactly such a thing right now for my little Taig mill,
as I hope to make simple PCBs and .010" just isn't close enough.)

Hope this helps.

Alan

P.S. Oh yeah, you'll need switches to establish a HOME position ..
and you might want a few more just outside the HOME switches to act
as LIMIT switches, for those occasions where

a. you weren't careful enough during setup to consider where the table
was going to move to, or
b. you weren't careful enough during GCode generation, or
c. you're milling pseudo-manually (finger on the jog button) and are
paying more attention to the cutter and the work than the position of
the table

P.P.S.

What did you buy ?


--
Alan Rothenbush
Academic Computing Services
Simon Fraser University
Burnaby, B.C., Canada


Before me things create were none, save things
Eternal, and eternal I endure.
All hope abandon ye who enter here.