From Scratch

Hello Everone
Usually I'd like to dig into problems before asking someone else help. But after making some research about Linuxcnc, I understand it would cost too much if I don't get help before solving this one.

We are a metal works company and planning to build our plasma cutter with the help of Linuxcnc.
Plasma table will be 1500x3000 mm in size
We drew the plasma table construction on cad software. No help needed about mechanics yet.

But we would like to know minimum electronics requirement to run the table smooth and perfect.
We only bought mesa 7I76-5I25 PLUG-N-GO KIT for this project for now.
So we need to know,

What PC to use with,
What stepper drives shall we get,
Do we need stepper encoders for this job,
Do we need THC, if so which THC would you suggest,
And we would like to know any other information about our needs for this job.

Thanks in advance
Best regards
Firat

I think in general you are better off with Ethernet connected I/O cards
for plasma machines so if using Mesa products, a 7I96 or 7I76E
would be a better choice for the step/dir and general I/O.

As far as motor sizing and types, there are some experienced plasma table
experts here that can likely answer your questions.

PCW thank you. But we already bought this plug n go kit. Can't we use it for plasma ?

Yes its possible, but you need to make sure you have no ground loop issues
or conducted noise from wiring It would also be better if the PC was in the same control case as the 7I76

thank you so we will separate the motion parts and pc.

Just an aside. I Was going to use NEMA 23's all round but then I found this NEMA 34 reduction gear So the price was less than what I would have paid for the parts to build a reduction gear for NEMA 23. So I bought the smallest NEMA34's I could find to keep within the maximum current of my stepper controllers.

Anyway back to your problem. Recognise that you may need to upgrade to a 7i76e but the available pins are very similar so start with what you have. Some pointers from my experience building a table from scratch:
1. Basic steppers are fine
2. Find the tech note about earthing a table from Hypertherm and follow it. Basically run an earth wire from every motor and every moving part back to a star earth point. Consider adding an earth stake the moment you have any RFI issues.
3. Put an IEC RFI filter socket on the AC input to your control box. Best thing I ever did!
4. Use shielded cabling to every stepper. Earth to cabinet ground at the control box end but leave ungrounded at the stepper end.
5. Use 5 wire connector sockets for the steppers at the control box. (I use microphone connectors). Pass the shield through one of these pins and earth it to chassis ground as close to the stepper controller as you can. I crimped on a spade connector to the ground, folded it back and held it in place with shrink tube and used it to connect the final earth wire to the cabinet ground.
6. As PCW said just get a PC motherboard that runs off a 12 V power supply and wire it in as if its just one more component. it will then be protected from the big bad world by the RFI filter on the IEC input socket.
6. Mount a Mesa THCAD board as close to the plasma cutter as possible as its frequncy output is designed to resist noisy environments.
7. Learn to compile LinuxCNC and use the Plasmac build.

Should I buy stepper drives or 7i76e is capable of driving steppers please ?

No, the 7i76e outputs 5 volt step and direction so you need stepper controllers. I use DM542a drivers from Longs Motor ex eBay. Stepper motors from stepper online who are global.

I understand. What about reduction for steppers? Which rack and pinnion is good to use or do you use gearboxes ?

And I saw alot of people use only 7i76e mesa card, I did not see 5i25 or others in their electronic enclosure. Do I need any other card other than 7i76e ?