That’s correct. I can jog around at 300 ipm, too much more and it will skip steps. However that’s more than enough. I think they are 84 Oz-in nema 17s.
That's awesome! I've mentioned a few times over at the LinuxCNC forums that I'm building with nema 17s and someone usually questions the choice. Hopefully I'll get as much milage out of them as you do.
It can be quite surprising when they see such an inexpensive machine rival cut quality of the $10,000+ tables. Rightfully so, most people don’t believe it until they see the results.
Being able to use book values with the Hypertherm which were developed for rack and pinion or ballscrew, Nema 23/34 or servo driven machines and not belt driven Nema 17s is such a good feeling. Early on when I was frustrated with my build and not getting the results I was seeing others with much more expensive machines attain I would just have to stop and look at the price tags over again. I don’t know how many times I looked at cnc router parts’ website wishing I had bought a pre-built one instead. Now I couldn’t be happier, and the same can be said for my wallet
The Plasmac component is a huge reason why my table cuts so well
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That is cool to hear from my side. I just saw that company’s booth at maker faire, they had a plasma running. The are amazing looking machines I see no issues with them. Lucky for me we cater to different crowds. When I see the “big” guys machines it used to kinda get to me, now it just reinforces exactly why I made the very first one. I don’t use my CNC everyday all day, if I did maybe at some point that kind of money would make sense. I have all kinds of tools now, none of them are top of the line, but I think I have all the tools I need now (crazy right!?) When I want to build or fix things I have my whole shop worth of tools including two CNC’s for less than the price of one of those machines. Plasma is the only thing I have left to get…and maybe a break.
I am glad you guys have stuck with it and figured out how to get this stuff working so well and I am excited to try plasma cutting out myself.
What’s great about the MPCNC project is that everything is already figured out. Not just the machine’s engineering but with the electronics and configuration.
There isn’t any one getting started guide for dummies that tells you exactly what electronics you need, how to wire it, how to configure software, etc for a plasma table. There is a wealth of information out there, but most of it assumes a certain level of technical knowledge of the systems involved. As a layman, sifting through the linuxcnc docs and electronic manuals and technical jargon and forum posts has been slow going. After I get this thing built I intend to make a write up of every little detail of what it took for me to get up and running with LinuxCNC. Hopefully it’ll be enough for new users to be able to follow along and get start burning metal in a much shorter amount of time.
[EDIT]
Here’s a frustrating example: I’ve happend to learn just now that there is a new mesas card in development called the 7C80 that is intended to turn a raspberry pi 3b+ into a viable linuxcnc computer. Looks like it’s expected to be released any time now. It would have been nice to have known that a week ago when I was spending so much time and effort exploring options for suitable old used computers when I have plenty of rpi’s laying around my shop!
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Actually my idea was to use Marlin to feed the torch voltage value so that it can be accounted for in the motion planner. I think that it can be used the same way that the bilinear bed leveling works, but instead of recalling values from the bed map from the memory, you’ll read voltage values in real time from the torch. This way you could adjust the height in order to compensate for warpage, but you could also plan corners and other special spots, because Marlin knows what path will be next so you could have some flags on specific spots, with various possibilities of adjustments. It would be a fully integrated solution, much better than any THC I could think of.
I think that the only thing needed here is some kind of voltage divider + some kind of filtering, in order to convert the high voltages from the plasma to lower ones, usable with the ADC of the Arduino. Then it’s just a matter of tweaking Marlin, which, according to Marlin’s guys, shouldn’t be very hard to do. They were opened to work on that, provided I could get them information about how the voltage divided would work specifically IRL, but unfortunately I don’t really know how to build the voltage divider. It’s not very easy to do at my little electronics level, you can’t just use two resistances and call it a day, there’s high frequencies involved… I’m not very comfortable experimenting since those power levels can be quite dangerous when you’re not sure about what you’re doing. So I just hope someone who actually knows that kind of electronics will jump in and come up with a solution.
Yes, this is exactly how mine is setup right now. Just a guess, but I think Marlin may have a hard time adjusting since it is a buffer driven motion planner. LinuxCNC is real-time so it can adjust the Z axis in parallel to other moves. The reason a Proma THC would work with marlin is because it’s totally independent. I could be wrong on this, but that is my thinking.
Are you trying to stay with marlin due to the availability/low cost of the hardware or is it some other reason?
This is what mesa has accomplished with the THCAD card. A third or better the price of THC and you’re still integrating it into your controller. To me it’s cheap enough that it’s not worth the effort/risk of trying to cobble together homebrewed circuitry.
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It’s real time relative to things like windows or standard linux, but it’s not as deterministic or as low latency as a microcontroller.
Marlin has a lot of advantages, starting with the fact that you don’t need a computer present and it is very inexpensive.
I couldn’t agree more. There are a lot of thing I take for granted in the hobby electronics that change a lot when talking higher voltage or higher frequency. The best thing is if there was just a way to copy the design of one that works. Maybe someone could convince Great Scott to do it. 
I can't really say for sure with my little knowledge. But the Marlin experts seemed to think it was easy enough to do, using the babystep function. No idea what it would imply specifically, but if those guys think it's easily doable then I guess they could be trusted :)
I found the discussion we had on their forum, here: https://github.com/MarlinFirmware/Marlin/issues/7562
For many reasons:
-Not having to swap my board whenever I switch from Milling or 3D printing to plasma, just reflash it with the correct firmware, change the toolhead and I could be good to go in less than 10 minutes
-Possibility to use the plasma machine with only the SD card, I don’t really like having my computer around whenever I’m doing stuff on the MPCNC, I always use the SD card. This is even more important in this case since the plasma cutter tend to throw a lot of EMF all over the place and spit molten metal everywhere.
-Super cheap board, the arduino/ramps is the best price/stuff you can do ratio
-Possibility to use the screen to tweak settings on the fly
-I’m already familiar with Marlin and Estlcam for milling. Plasma cutting is almost the same process so I’d prefer not having to learn a new complicated tool again. Everything worked fine with plasma cutting last time I tried it, the only issue remaining was torch height control.
I’ve seen it but it doesn’t seem to work the way I want. The output is a variable frequency, what I’d like is a variable analog voltage. I wouldn’t know how to make that work. Also, it’s quite expensive, at that kind of price I guess I could spend the extra buck and go for a “real” THC.
Yeah… it feels funny converting the input voltage to a frequency, only to be converted back to voltage at the controller. Though I figured this has to do with safely isolating the plasma from the electronics. Would frequency readings be more accurate over a length of wire than voltage readings due to voltage drop, emi, etc?
Lots of extra bucks. A “real” THC would be at least 3x the cost, though I have no idea what shipping would be like going to China. But, with the Mesa cards in hand, these things are the real deal! I’m used to handling cheapo imported boards and this ain’t that. I just wouldn’t want anyone to have the impression that we’re cheaping out on quality.
Integrating THC into an Arduino controller would be a very cool setup. It would really lower a few barriers to entry.
Yes. Anything that depends on the edges of a digital signal would be more resistant to emi. Even duty cycles, measuring the time delta between a rising and falling edge will be affected by emi, triggering a little early or late. CAN bus uses a differential signal for high noise environments (cars and trucks), and the signal is digitally encoded.
I’m not sure if Marlin can read that signal fast enough. 1MHz is fast enough to be trouble. I’m not great with embedded software, but I am guessing it would at least be a sacrifice of an interrupt, which are often hard to come by and pretty hardware specific.
You could put a slave arduino to read the frequency, and send it to the marlin one, and put them both in a metal box. That’s the simplest solution I can think of ATM.
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At the maker faire this year lightburn is now controlling there nozzle height with an some sort of range finder. I know plasma has a lot of sparks and smoke, but so does laser, well fire. Maybe have a look at there page and see how they are doing it. The setup seemed to work really well. Maybe a full time induction probe, laser range finder?
That looks cool.
I wonder if you could achieve the same with an ultrasonic sensor, or if there would be drawbacks Ie. delay / interference from arc.
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That looks like it would work well.
I would assume a proper shielding of the cables and enclosures could be enough to get readable values, with a little filtering. I don’t think you need insane accuracy here, the cutter will work fine between a couple of millimeters. It will impact cut quality a bit but as long as it cuts you can still massage the part a little with a grinder to get proper finish later.
Well here in China you can find THCs for around 100-120 bucks. No idea if they are any good but it’s not that much more. Plus you’d need some kind of interface to convert the signal from a frequency to a voltage, so that’s another Arduino (not very expensive, but still) and some more complications/cause of failures harder to diagnose.
I’d rather prefer going for an easier DIY solution, if possible. I’m pretty sure it is doable with a few basic components for a fraction of the cost, but I’m not good enough with electronics unfortunately. This guy seem to have made it, but I’m not clear enough on his circuitry. I tried to reproduce his circuit on Falstad but it doesn’t seem to work fine, so either Falstad doesn’t work well (which is sometimes the case), or I did something wrong, or either his circuit doesn’t work… I don’t really want to find that the hard way…
https://tamarisktechnicals.com/pages/CheapTHC.html
Anyway, that’s not for a soon future, I’ll have to move out of the place I rented those past years so that will be a big stop to all my projects for a while…