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Offline stirling

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plasma torch control
« on: December 09, 2007, 08:02:57 AM »
Hi - Can someone give me a brief lesson in how this works/ties in with Mach please. Things like...

turning the torch on and off - presumably this is similar to spindle control?
how do you tap into the torch to "read" arc voltage for THC?
Can this be done with any torch or do only some have this "output"?
Presumably I need some (AD converter?) hardware between this and Mach?

TIA

Offline stirling

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Re: plasma torch control
« Reply #1 on: January 14, 2008, 10:50:13 AM »
bump - anyone?

Offline Chaoticone

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Re: plasma torch control
« Reply #2 on: January 14, 2008, 09:36:08 PM »
Hey Stirling, I know very little of this, but will try to play with it a little tomorrow if no else has you fixed by then. Keep bumpin this thread, someone knows all of this allready.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: plasma torch control
« Reply #3 on: January 14, 2008, 09:46:06 PM »
To make a THC that actually works fast is a very complex task, commercial THC's cost ~$8k but here is one that people say works just as good or even better: http://www.candcnc.com/MP1000C.htm.

I will be buying one them in a little bit as soon as my plasma table frame is finished.

Offline stirling

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Re: plasma torch control
« Reply #4 on: January 15, 2008, 04:21:06 AM »
Hi Brett - thanks.
Hi DennisCNC. Thanks for your response  - Can you expand a little on what you mean by fast is complex?
I've looked at candcnc's THC and had discussions with them. The problem is that over here in Europe we've just had a law imposed banning whats called none ROHS compliant electronics. Candcnc quite understandably havn't enough business in Europe to warrant the time and money involved in getting compliance. I could have bought one prior to 1st Jan this year but as I explained to candcnc I'm looking for an oem supplier for ongoing supply/business reasons not just a one off.

It's because of all this I'm looking into what's involved with a view to designing one or having one designed. To be honest - at the moment I can't see why they're complex at all...

if voltage > reference then
  output a THCup to Mach
elseif voltage < reference then
 output a THCdown to Mach
endif

sort out touch off and pierce height and job done...

OK maybe now I'm expecting some "It's not that easy" comments - but can anyone say why it's not that easy? - I've tried asking on the zone as well but it seems either no-one knows or no-ones saying :-)
Re: plasma torch control
« Reply #5 on: January 17, 2008, 10:48:09 PM »
This RoHs stuff is a pain for all you in Europe,  If you plan on cutting I would say under ~40 IPM you can make one like you mentioned and it would work ok as long as you figure out how to have a clean arc voltage signal from the plasma.   Have you seen the Plug-in Brian made for a THC:http://www.machsupport.com/artsoft/plugin.htm

The higher power plasma you run the harder it will be to control it as more noise will be generated and if the arc fires above the material too high the voltage will spike high also.

I meant fast like ~200 IPM and staying with in 1 volt of the ~250 volts of the arc.

Offline stirling

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Re: plasma torch control
« Reply #6 on: January 21, 2008, 07:06:16 AM »
Hi DennisCNC - Thanks for your response.

I guess the bottom line is that candcnc seem to have managed a cheap and (from what I hear) effective solution, so it's obviously "doable". I took a look at Brian's plugin but couldn't figure out how to get it to do anything.

Cheers

Ian