Re: [CAD_CAM_EDM_DRO] Re: EDM retrofit

Graham Stabler wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "WGB" <witekgb@...> wrote:
>
>
>>Does anyone have any info or do you know of any links that will help
>>me with this problem. I am thinking of buying an older wire edm
>>machine and replacing the old CNC control with a Linux EMC
>>controller. Has anyone done this? What are the issues with EDM. I
>>really do not know much about wire edm but I would like to get one for
>>my home machine shop, however I would prefer to use a commerical unit/
>>with mods rather then build from scratch. Any help would be great.
>>
>>
>It is far from straight forward as the feedrate needs to be altered
>with varying gap conditions, even reversed when needed. You would
>have to work out how to drive the generator, what feedback is used
>(voltage, current or ignition time) and then probably rewrite much of
>EMC to make it happen.
>
>

I don't think you'd need to rewrite much. The current core of EMC2
can't handle reversal (along a G-code path), which is the main issue.
There are hooks for reducing feedrate based on external stimulus - you
just need a way of getting the data into the software (such as an A/D
converter). Once EMC2 has the information, anything can be done with
it. There's an input to the motion controller that does adaptive
feedrate override, in realtime.
If something custom is needed, that's not a problem either. It's
trivial to write new components for special functions - they can be
compiled and installed with a single command (you don't need to
recompile all of EMC2, just the component you're adding). (see
<http://www.linuxcnc.org/docs/html/hal/comp/index.html> for more info)
Of course, trivial is relative - you have to know what you want the
machine to do given whatever feedback conditions you have.

>You can buy replacement controls for wire EDM machines but these will
>cost much more than the machine itself.
>
>At the moment there is no DIY route to proper wire EDM though a few
>people are working on it including myself (though it is well on the
>back burner).
>
>

At the moment, I believe reversal is the only thing keeping EMC2 from
being fully capable of doing EDM control. It's a pretty big thing, so I
don't expect full support for it any time soon. We usually try to make
any implementations generically usable rather than single-purpose, which
sometimes means features take a while to get implemented. For EDM, you
only need to reverse for a few thousandths of an inch. To remove a
broken dovetail cutter, you may need to reverse inches, through multiple
G-codes. A simple solution to back up a few thou would be - err -
simple :) A general solution to allow you to reverse as far as you want
(possibly to the beginning of a program, while properly handling G2/G3,
cutter comp, other modal codes, etc) isn't so easy.

- Steve