CIgweld Cutskill 60 - adapting to CNC use

When you say "half the resistance on each wire" if we take an example where I am setting up a THCAD-10 to max scale at 200V then I believe I need 1.9M Ohm (based on the forumula in the manual). So per you suggestion I have 950k Ohm on the POS and NEG input wires of the THCAD - yes?

Where
THCAD Input NEG ---> Torch
THCAD Input POS ---> Work clamp

Re the metal box on the back of the plasma unit, that was what I had been thinking but changed it based on the non HF description in the plasma primer. I take it what you are suggesting is a bit more conservative/safer?

Cheers - J.

Joco wrote: When you say "half the resistance on each wire" if we take an example where I am setting up a THCAD-10 to max scale at 200V then I believe I need 1.9M Ohm (based on the forumula in the manual). So per you suggestion I have 950k Ohm on the POS and NEG input wires of the THCAD - yes?

Yes

Joco wrote: Re the metal box on the back of the plasma unit, that was what I had been thinking but changed it based on the non HF description in the plasma primer.

Oops I wrote that!

If you look at a plasma machine that has raw arc voltage output (eg Thermal Dynamics, Esab, Everlast) Typically they add 100K resistance to each terminal to reduce the current to a non lethal level. This resistance (200k) must be counted as part of the THCAD scaling resistance.

I did set my 120 amp Thermal Dynamics up to use Raw arc voltage for fun when I first got it with the THCAD in the control box and it worked fine. So in answer to your question, reducing the current with the scaling resistors inside the case reduces the current to non lethal levels so its safe to route it to a THCAD in the control box.

But on the flip side, on a machine that is not designed for CNC, to my mind locating the THCAD at the plasma cutter provides a more robust solution. If you do do this, it must be powered from the Control box to avoid noise and ground loops. The plasma cutters i've opened all seem to have a bit of room in the cases so if I could, I would avoid attachments on the plasma case for cleaner install.

Rod - plasma primer is awesome. Great job.

Get the logic for install close or in machine. If inside the machine assume you just have it on mounting bracket? Not in a box?
For hypersensing do you also put that THCAD in the plasma unit given its going to have wires to it with cutting voltage on them? If so it might start to get a little crowded. The cigweld unit is pretty compact already. But it will be easier to visualise when I get the parts.

Question on control board, obviously going with mesa but 7i96 or 7i76e? I like the tighter price of the 7i96 but will I run into issues with limited IO?

Cheers - J

Joco wrote: Rod - plasma primer is awesome. Great job.

Get the logic for install close or in machine. If inside the machine assume you just have it on mounting bracket? Not in a box?
For hypersensing do you also put that THCAD in the plasma unit given its going to have wires to it with cutting voltage on them? If so it might start to get a little crowded. The cigweld unit is pretty compact already. But it will be easier to visualise when I get the parts.

Question on control board, obviously going with mesa but 7i96 or 7i76e? I like the tighter price of the 7i96 but will I run into issues with limited IO?

Cheers - J

Yeh inside, I'd just mount it on standoffs or some kind of bracket if required.

The hypersensing thcad would still live in the control box. Mine does. It needs the power and everything and connection to star ground point so it will be better there.

For someone like you who can't help but take things to the next level, I'd get a 7i76e. I've used all of its inputs I think. My Lam Technologies stepper drivers consumed 4 inputs and 4 outputs and then there is my hard wired pendant...... Use the spindle relay to trigger your torch.

Thanks.

Next level? Who me?

Star grounding, is that something in the plasma primer? Have read so much stuff I'm loosing track of what is where. I can remember seeing it mentioned but have not bottomed out an "explanation for dummies" as yet.

I think we did it to death here
forum.linuxcnc.org/plasma-laser/36734-le...ring-and-emi?start=0

Its easilly overlooked but does make a big difference. the intent is to create a seperate path from the torch holder and each motor over any sliding part to drain away any emi back to a central ground point.