Plasma cutting

Hi guys,

I would like to experiment the MPCNC for plasma cutting.
I don’t know much about plasma cutting so far, I’ll purchase a cheap 40 amps plasma cutter this week and will try to fit it in the MPCNC.

Did anyone try this before? Do you see any particular reason why this shouldn’t work?
Any useful recommendation?

I believe I should use it basically as if it was a laser cutter, so do you have any programs that could generate the paths and activate automatically the machine at the right time, so that it won’t cut during travels?

Any advices are warmly welcome!

There are a few videos plasma cutting with the mpcnc, last I remember there were some grounding issues maybe, could have been the old rapids software issue as well.

There are a few threads about it on here, but I wouldn’t mind setting one up myself now. If I can get the LowRider CNC kits out I will have a bit of time to mess around with it.

I think a bit of post processor edits will be required for things like pierce dwell time and your trigger wiring.

The start up style matters, maybe HF start. Just a guess but it either needs to touch or have a ground wire maybe. Sorry for all the speculation but that should get you going. I will be following along for sure. I will offer any assistance I can. (checking amazon for plasma cutters now.)

A lot of the guys over on the plasmaspider forums use a magnetic ground clamp for their work. Seems to work well.

if you were to try this, please do yourself a favor and use shielded cable for everything. HF can play hell on electronics. Also, don’t share computer/ramps grounds with the plasma grounds.

Long term i don’t think the mpcnc would be a good plasma cutter without a torch height controller. If you are vigilant in keeping the material extremely level, it would work without one. Thin material warps easily when being cut. I would assume that you need lots of speed as well for thinner stuff.

Thanks for the advices guys. I’m indeed very concerned about grounding, since I had the issue already with my shop vac.

In my opinion, worst case scenario, I could use a few 12V batteries to power up the ramps, so that they are on a completely different power network with the cutter. I have shielded cables but I didn’t put them to ground, maybe I’ll do that if it turns out that I have issues.

For leveling, I will probably build a new bed just for that, since I cannot use the wooden one anyway.
I’m not concerned too much about it, but that may be because I’m totally inexperienced. Anyway, I think I can find some solutions to overcome this issue, either by lowering the amperage, finding a good way to clamp everything , some active cooling or just by increasing the cut speed (the MPCNC can move pretty fast from my experience).

I purchased my cutter today, I hope it 'll work!
I took the cheapest one, 40Amps version, here:

It is supposedly ok for a maximum of 12mm steel sheets, which should be more than enough for me. I think those things can cut any kind of metal, right?

Plasma is very high temperature, it will pretty much cut any metal as long as it’s thin enough. Keep us updated! Good luck!

Ok, I received my plasma torch yesterday. Made a few manual tests to see if it works. Cuts stainless steel sheets like butter!

I think I will have an issue though: apparently the torch needs to get in contact with the plate in order to initiate the arc. Then it can be lifted. I suppose this is because it is difficult to go through the initial air resistance, which probably decreases a lot once the arc is started due to the heat.
So I think I will need to find a way to generate this particular movement in estlcam: plunge until it touches the plate, then lift up a little and move around the path. Is this feature available in Estlcam? any easy way to do it?

Also, i’ll have to think about my support table.
I saw a few examples around youtube and I’m particularly interested in the ones that contain water.
Problem is that I know close to nothing about that, so any suggestion here again is welcome: how would you do the table ? Keep in mind that I need to protect the wood of the CNC structure so some kind of enclosure to protect the bottom from sparks is necessary.
I have a few ideas but more brain power is always welcome !

Keep in mind Im prob not exactly the best person to be chiming in here but…I would think you could create a start code and program it into any software including estlcam that would do as you directed. Basically it’s just like an end code (i.e. home all axis ) but right before the job.

Yes, but the issue is that it needs to do this move before any cut, not just at the beginning of a job. If a job has for example 3 paths and two travels between, then it will need to do that 3 times, one at the beginning of each path.
I could do that manually by editing the gcode file, but it would really be a pain.

Basically the logic is pretty simple, I think for anyone who knows a bit about coding it should be pretty straight forward (unfortunately I don’t):
-move the head over the beginning of the path.
-lower Z axis until specified zero height (the plasma cutter should touch the metal)
-activate the plasma cutter relay
-move up z axis by a few millimeters (this is for having a bit of clearance and not ruin/corrode the electrode too fast)
-Start the path
-Once we reach the end of the path, shut down the plasma relay.

I think it is almost the same as for any laser cutter, except the little head lift before each path.

Yeah, it wouldn’t be hard to do it in a postprocessor. There are some Python libraries that understand gcode. You would basically be going through line by line, keeping an eye on the z axis. When it goes down, you would make it go further down, then back up a little. In a one depth gcode file, the only two z heights would be cutting depth and clearance plane.

G00 Z5.0

G01 Z-1.0

G00 Z5.0
M105 ; turns it off

G-2.0 ; touch
M103 ; back on
G01 Z-1.0

You could do that with a text search/replace too.

I’m not sure if it is the style you bought or if it is possible with your machine but this was tackled a few ways in the other plasma thread. That is what I meant about the HF start or dragging a ground wire.

You also might be able to just get it with some creative CAM, like make a hole plunge at the beginning of each cut and then up a bit for the outline? Not sure. One of these days I’ll take the hit and buy a plasma.

@vicious, I though about that, the only problem being that in estlcam you can’t decide where your path will start, the machines will decide it for you.

Anyway, I have a very good news: turns out I was just stupid and I could actually start the spark a few millimeters over the surface. So, problem solved, it can start without having to actually touch the plate!

I’ve printed the support for the torch, I just need to design a nice table now. Maybe I’ll do a few tests with a crappy table first to make sure it works before investing money and time in a clean setup

Question: should I use some particular protection on the 3D printed plastic parts? I’m particularly wondering about UV light, since PLA is quite sensible to this, as well as temperature.

If I need to protect them, I plan on using some aluminum tape, which will reflect most of the radiative part of the heat, since I don’t think convection will be a big issue here.

Again, any thought or suggestion is welcome

In estlcam you can chose where it starts and you will also need lead in and lead out.

Great, I didn’t know that.

What do you mean by “lead in” and “lead out”?

I show it here,

Oh, great, that’e exactly something I had in mind and wanted to do to get clean cuts!

Thanks a lot for this information, I feel quite stupid since I’ve saw this button all the time and never even wondered what it was for… Same thing about the start path button…

Thanks again!

Ok, I built a new Z axis for the plasma cutter.

I think I’ll do that now for tool changes, instead of taking the tool apart, which necessitate to take off some screws, unplug everything and waste a lot of time, I’ll just swap the entire axis which only takes a few seconds and doesn’t necessitate any further adjustments. I simply hit “move axis” and the Z axis will pop out by himself eventually. Then do the reverse operation to put the new Z axis back in place. Easy peasy.

Anyway, here is how it looks like, nothing very special.

Here is the plasma cutter I’ll use. I purchased a straight torch so that it fits better on the CNC.

I’ll now need to protect the CNC frame from the hot metal sparks who will eventually fall on it, wire a relay to activate the torch and do the first tests.
Maybe this weekend if I have enough time.

Looks great! I can’t wait to see it working!

Interesting that the head has to touch the metal first… We have 20’ Lockformer plasma tables at work and we set them to nickel height. Literally put a nickel on the metal and drop the cutter head down on it and lock it. When it moves the head uses pneumatics to lift and when it cuts it just drops down and hits the stop you set. The head never touches the piece to be cut.

I can’t wait to see yours work. Although I have these big cutters at work I’d love to have one at home too.