Re: cheap edm tap buster?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Paul Kelly" <tech@...> wrote:

>
> In the spirit of "I've no daily use for EDM but if it were easy, or

I could

> use the kit for something else as well..."
>
> Strikes me that a plasma THC and basic software control (ie mach3's

THC

> code) could manage the spark gap.. And then you have a THC unit too..
>
> PK
>

Paul: If the EDM can be setup to provide constant current then it
would work. THC is based on the fact that the plasma (and TIG)
process uses constant current and the arc gap voltage varies with
distance. So in those machines the voltage changes to try and
maintain the same current across the gap. If the power source lets
both vary then you lose the ability to determine the arc length.

On the other hand if you used a regulated voltage (constant voltage)
and measured the current then you would have an indication of the cut
and be able to provide a constant cut and feedrate.

Since it sounds like better cutting can be obtained using a pulsed
current with high peaks then the control would need to average that
out.

The voltage (if you used the constant current approach) variation and
amount would proabably be below the normal levels of plasma cutting
(79 to 160VDC). While the Digital THC will go all the way to zero the
resolution of 1 volt might need to be be dropped. In plasma anything
below 50 VDC is considered a "fault" an ususally indicates a tip
crash. That parameter would need to be changed too.

I have though about offering an EDM electronics solution for the Small
Shop but offers in the past have been met with luke warm response.
It's difficult to embark on an enginnering project when the scope of
the market appears to be so limited. Not using it myself I have to
first understand the physics behind the process (beyond the obvious).
Since it's arc based there has to a lot of simularities with plasma
and TIG but it's the technical details that are hard to gleen.

Tom Caudle
www.CandCNC.com