LR3 plasma cutter build in New Zealand

It’s time for another lowrider… I built an LR2 about a year ago and then at the start of this year began printing parts for a second LR2 to use as a plasma cutter. I kinda stalled with the build as work got in the way then saw the teaser pics of the LR3 and that got me fired up again.

I’ve now printed all my parts and am working on the plates. Will start with printed XY and MDF or plywood YZ and strut plates but may upgrade these to aluminium.

Thanks to @darxide @kd2018 and @uthayne your plasma builds have given me a wealth of information to get started. I’m planning on using linuxcnc with mesa 7i96 with THCad as my controller. This will be a big learning curve after the skr-pro on my last build so will go with Kyle’s detailed build log for the electronics.


I’m not current on the latest in the linuxcnc front but some things I know that change since my log are qtplasmac should be easier to install than PlasmaC that I did the write up on. User guide: QtPlasmaC

… aaaaaand I was about to mention to use a specific distro besides the default debian but it looks like there are presently issues Installing LinuxCNC on other Linux distros does not work anymore - LinuxCNC

Keep an eye on the linuxcnc forums and they’ll set you straight. Post 2 in the linked thread shows someone is currently working on an updated installation guide… And fwiw all the people posting in that thread are plasma people.

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Thanks Kyle.

I installed Linux Mint 20.1 last year and installed LinucCNC which seems to be playing nice but hadn’t got as far as connecting to Mesa card and steppers.

I’ll have a read through these links and give it a go once I’ve wired up the drivers.

I’ve read up a bit on the linuxcnc forum and definitely found them helpful.

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That’s great, if you’ve got it setup stick with it! I’d mess around with the updates in a virtual machine or a testing machine first to get a handle on everything.

I look forward to seeing to your build. Have you thought about a design for a floating torch head for the lr3?
@vicious1 same question to you

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I’m pretty happy with the THC, not sure if a floating head would add anything? If anything maybe a breakaway.

The float is just for touching off. You’re using ohmic for touch off?

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In qtplasmac a float switch acts as backup to the ohmic should it fail and doubles as a breakaway when not touching off. Point being maybe the mount could be designed to use a single switch to accomplish both goals anyway? Maybe setup normally closed and then either mount floating OR falling off would open the switch… idk


The new LR3 core looks perfect for a straight machine torch, unfortunately I just have a hand torch for now.

Back in January I had started working on a floating mount for my hand torch on LR2 also with a magnetic breakaway as further level of safety.

I’m back to scratch now creating a new mount for LR3 core and definitely like the idea of a floating head.


I like where you went with the lr2 version! One lesson I’ve learned the hard way is it doesn’t take much spring pressure to function as needed, and it doesn’t take much spring pressure to warp the PLA over time. Next time I will adjust the spring so that the mount is under minimal if any pressure at all from the spring when at rest.


Good advice on the springs, the one’s I have are probably way too strong. I’ll probably go through a few prototypes before I get to a good design.

Now I need to get my head back into where it was at 6 months ago on the Linux and controller setup before a long pause!

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I am trying to dream up a water table. I think I want to have two LR3’s, but in the same footprint. Lift off the wood one when using the plasma. My buddy just called yesterday and wanted too plasma cut some stuff but I have it all apart…to finalize the LR3. Time for more plasma now that it is done!


Look forward to seeing what you come up with for convertible LR on same footprint. My plan is to have a separate dedicated LR3 plasma cutter in my welding area to keep the sparks and water completely separate from wood and dust.

I’ll post my table design soon, I’m open to any suggestions before I commit to the final design.

Looking forward to this build. I recently built a system running Linuxcnc on a rpi with mesa. Was going great until a slip of a screw driver totaled my mesa card. Please document this build as much as possible.


Down draft table might treat you well Ryan. You just have to ventilate and you will not get near as contaminated cuts. If you have a saw dust system, you might be part of the way there.

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Be careful mixing the two lest you end up with a thread like MPCNC Not Fireproof


Here’s my first draft of table design for the plasma cutter. I’m planning on using mostly 50x50 and 75x50 RHS as that’s what I have left from previous jobs. 75mm deep water table with the top of slats 20mm below the top of rails which Y rails mount to give a bit of clearance for splashing without compromising on the lowrider staying low in z if that makes sense.

I’m limited by space in my workshop so am designing for a 900x1250 workspace to fit 1/3 of a sheet of steel. Would love a bit larger sheet size but that’s what I’ve got.


I like that.

I had not considered running the slats lengthwise…makes so much sense. Less cutting and we have relatively small builds so the rigidity is still there. I need to find a local metal shop to get started on mine. I think I will aim for what you have just drawn up!


Biggest advantage I find with running slats along length is when loading material, you can slide the steel plate along the slats from the front without it catching as it hits the edge of each slat if the run across.

I’ve got a couple of minor tweaks then I’ll post a more detailed plan.

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I had not even thought of that!