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This thread might take a fair while to develop. Its been 12 months in the making already. My Arduino Rotary table controller project got me interested in CNC but I did not want to do the obvious and convert my mill to CNC. I eventually got interested in CNC plasma cutting and I started about 12 months ago by cramming the electronics into an old Plasma machine case complete with a Torch height control.

Wow rod, I wish I had seen this thread from the beginning. The person I bought my Milling machine from had a CNC plasma machine in his garage. I got to look at it in detail and decided I'd really like one, one day. I wonder if it's worth it for a smaller table size... versus getting 3/8" plate waterjet cut...

anyway, looks like I will be busy reading about your adventure
I can tell you want one!

You only need about 90-100 psi. This Thermal Dynamics A120 uses 189 Litres per minute (7 CFM). My single phase compressor produces 320 litres per minute (11 CFM) FAD (Free air delivery). This one is a bit old school and has a manual regulator built in and a set of LED's showing the pressure. You flick a switch to enable the air flow and set the pressure based on the LED's to suit the material to be cut then flick back to cutting mode.. That cut was at 80 psi. The Hypertherms control the pressure automatically. I had the compressor and its only new. According to the air shop I got the dryer from its a bit undersized. He said your compressor should have double the air flow of what you need to reduce cycle times.

You do need a source of clean dry air so I think you should add the refrigerated dryer to your shop air. Some people do use Dessicant dryers and a toilet roll filter (Motorguard filter) right as the plasma. You will save a lot of money in consumables with the refrigerated unit and it has pre and post filters on it so there is no filtering required in your whole shop.

I defnitely need to finish off the downdraft hopper or you could run a water table to catch the mess. There is black dust everywhere!
Wow rod, I wish I had seen this thread from the beginning. The person I bought my Milling machine from had a CNC plasma machine in his garage. I got to look at it in detail and decided I'd really like one, one day. I wonder if it's worth it for a smaller table size... versus getting 3/8" plate waterjet cut...

anyway, looks like I will be busy reading about your adventure

John, There are plenty of small tables out there. You have to be sure you can get plate steel cut down but you can cheat like I did with flat bar. for 3/8 you could get by with a 45 amp plasma cutter. Hypertherm 45XP or Thermal Dynamics/ESAB A60i. Here we'd use a laser cutting service for that job. It should be cheaper than waterjet. The side rails on my plasma cutter were laser cut from 12mm (1/2") to get exact hole positioning and the M6 holes came back ready to tap but the M4's they etched for position and I had to drill them. Thinner material will let them cut holes ready to tap down to M4 though.

I will say that a plasma table sounds simple enough but in hindsight its probably not ideal for your first CNC machine unless you purchase an external torch height control. But I think what I've achieved in software is superior to what the external controllers can achieve and the voltage sensing board was only USD $69. What I did not understand was that plasma support was not well supported in LinuxCNC (as its kinda an orphan CNC process) but since I started its come ahead in leaps and bounds with several projects on the forum which are bound to get good plasma control into the base source code soon. There is a more complete build here
John, also the plasma spider forum is a good source of info. I weakened and put a briefer build thread there too
But the forum is very Mach3 oriented. They have no idea what we've been able to achieve in LinuxCNC... Stuff that leaves the commercial software for dead.
Well of course I "want" one !

But I do not have the room for anymore stuff in my shop :(
If I do end up with a bigger shop, my compressor should handle it. I have a 70's vintage LeRoi-Dresser 400 series it is spec'ed at 23cfm at 175psi. And I just rebuilt the pump a couple years ago.
I do a lot of sandblasting and needed the cfm.

Well its been a while since I updated this thread. Once I upgraded the machine, I needed to do 2 things. Add a larger drag chain for the larger torch cable and also to install ohmic sensing to sense the material height more accurately than my float switch.


The plasma cutter came with a clip to connect a wire to the torch shield. Note this is not the actual electrode tip but a protective shield that is isolated from the arc voltage.

The Ohmic sensing took a lot more work than I expected as it required a seperate isolated power supply and a three optoisolated relays. 2 of these isolate the probe circuit while cutting and the third switches field power to an input n my Mesa 7i76e when the torch touches the material. I also added a small circuit board with some protectivediodes and some LED indicators which are now redundant as the relays have LED on them anyway!
IMG_20190428_182050 (1).jpg

I've spent a fair bit of time with some plasma enthusiasts in the Linuxcnc movement working on a new plasma controller written by Phill, a fellow Aussie. He has been amazing with the features he's added from feedback by people like me and there is now no point buying a commercial controller as this is that good and very easy to install.


Whats so unique about this config called Plasmac is that all control is built into the GUI so the plasma cutter just receives a M3 command to start and all probing and torch height control just happens. I have not shown it here but on the Plasma Run tab, I have a list of about 50 cut charts that can be selected from G code or by walking up to the machine and choosing your material from a dropdown. It also has a Statistics tab which tracks the number of piercings and distance cut so you can monitor consumable life or gather data for quoting purposes.

Today I wrote a Sheetcam post processor which found a lack of error checking and while I was workin on the Post, Phil added some clever error checking that checks for invalid tool selection in G code before a cut is made. (Which you can see in the screen dump)

But proof is in the pudding. Here is a part I cut yesterday on a steeply angled bit of material and it had no trouble following the material at the 2mm cut height I was working to just be reading the arc voltage and using a PID loop to control height.

In the next post I'll add a couple of videos but it looks like its about time plasmac did the obligatory cutting of a sheet of corrugated iron!
So here is a video cutting the part on the slope.

And a bit of a walk around my machine

Do you have a link to the Plasmac controller?

Yes, on the very first post on this thread there is a link to the repository on github

There are some instructions on how to install it on this thread I wrote

Recommended hardware is a Mesa 7i76e ethernet board and a Mesa THCAD voltage interface but it will work with external hardware like the Proma. You can get that here or from Mesa direct.

It currently requires compiling LinuxCNC from source and I recommend that you start with one of these ISO's (probably the latest AMD64 one for 64bit hardware)

The main reason why it requires compilation is that its included the reverse run branch that is not in the core code and Phill has added it to his repository. This lets you step back and forward through the gcode when paused which helps with error recovery if a flameout occurs. Eventually, I think this will become a part of the linuxcnc core distribution as we are now just tidying up the last few things including a Sheetcam postprocessor I finished writing yesterday.
Very Cool !!

I know it has been a lot of work but your results are outstanding. Thanks for your efforts, kind of makes me want to build one :)