DIY Arduino THC - Video

[furkanyilmaz]

Hi EmptyNester,
If you still have any of the mega shield boards for sale , I'm interested.
I just found this thread yesterday and read it all the way through. Great work !! I have a different brand of plasma cutter but I'll try to work out the voltage divider. I've been searching for a while for an Arduino flavor THC and it sounds like you've nailed it down.

Hi Cwalker I am currently working on this project and it didnt work yet. Could you help me? I have same problem about Mach3 plugin but my real problem is about eagle. Did you print the pcb from eagle or did you redesign it?

[none]

Although this thread looks abandoned I would like to ask anyone here who tested this Arduino THC system about connecting the Shield to the PC. This info is not really in the user manual. I know there is a micro-USB socket on the shield but does that mean I have to connect the shield to the PC with a micro-USB to USB cable? The shield will be connected to the USB cable on the PC? Or I need to get a micro-USB to DB9 cable? There is nothing in the user manual about this.

Thanks

[EmptyNester]

Although this thread looks abandoned I would like to ask anyone here who tested this Arduino THC system about connecting the Shield to the PC. This info is not really in the user manual. I know there is a micro-USB socket on the shield but does that mean I have to connect the shield to the PC with a micro-USB to USB cable? The shield will be connected to the USB cable on the PC? Or I need to get a micro-USB to DB9 cable? There is nothing in the user manual about this.

Thanks

The micro-usb on the Arduino board is only used for programming the board. (I've had more success programming it with the shield disconnected during programming.)

The PC connects to the USB to serial adapter you mount on the board.

You really don't want to connect the PC to the Arduino's micro-usb connector during operation because that is not isolated. If you do connect to that port and there is something wired wrong or something fails, you could end up with your torch voltage (110 V +) running into your PC. The shield contains optical isolators that connect to the USB to serial adapter and the adapter is powered from the USB power line. This allows data to be transferred between the THC and the PC with no direct electrical connection.

I think that should be address in the section about isolation, though I haven't looked at it in a while.

[meJasonT]

Hi Guys,
Im new to the site and not quite sure where to ask my question, so sorry if ive gone off the reserve on this topic.
i have built a CNC table and im trying to get my head around the Plasma cutter before hooking everything up.

Ive purchased a cheap ebay plasma Cut50, i had no choice - down to cost and demand.
Im wanting to incorporate the Arduino THC which leaves me with a couple of questions.
the voltage measurement is it taken from the torch and earth clamp connectors and i would be expecting to get something like 200v to 300v.
my other question is more of a request really.
The arduino is something im familiar with and ive started to convert my milling machine into a CNC using GRBL (an open licence CNC code and front end built around the arduino) the problem i have is that the Arduino THC is built to interface with Mach3. I am considering reworking Regeg's Arduino THC code so i can turn the arduino THC into a stand alone unit which will directly drive a motor itself, it would then only require a torch on/off command and a error/reset signal to indicate an arc loss etc.
the question is how can i get in touch with Regeg (https://github.com/regeg/ArdunioTHC).

And just to show my ignorance i have a real newby question.
i dont have a clue what plasma ive bought:-
i think its a HF one with no pilot start as i have to make contact with the work piece before it arcs
ive found a site where a guy has connected an earth clip to the torch tip to create a pilot arc before cutting.
is this a feasible solution to not having to contact the work piece to start the arc.

i guess the alternative would be to use the torch on command to start a process where the THC would drive the torch to make contact and then lift it to correct height after a certain time period. If its possible to generate a pilot arc with the earth clip onto the tip then the THC could make the earth circuit to pilot the torch then once the arc strikes disengage the pilot earth connection.

i tried to find pilot arc circuitry/schematic on the tinterweb with no success, so i will be experimenting any time soon.

look forward to any feedback or suggestions.

[Rambozo]

A couple of things.

Yes, you could have a THC directly drive your Z axis, with the right code. The basics would be pretty easy, but there are subtleties that would take some tweaking. This could probably be handled by a single Ardunio, depending on your stepper or servo drives. Or you could split the workload between two if you are doing all the low level motion control in software.

Depending on how you are generating your g code, you might want something with a little better front end like Mach or LinuxCNC to give you a nice MDI, preview and other features that are good for hobby machines. Even something like a Raspberry Pi can make a good front end to an Arduino motion control solution. Then you have enough memory and processing power to work with more complex files and be able to keep up.

Voltage to a THC is typically fed from a voltage divider, either built into the plasma unit or by an addon board installed inside.

True pilot arc is somewhat built in to the design, not that easy to add. Starting can be blowback, high frequency (not recommended for CNC), high voltage, etc. This is somewhat easier to make changes to, if you want to go from one to another.

But the big issue is that low cost plasma cutters and CNC do not mix. The duty cycle is way too low and they die in no time. So it's not worth investing any time in improving your unit. If you want to use it to build your CNC and THC and get all the bugs out before buying a good plasma unit, that's ok. You don't have to worry as much about blowing up something expensive while you are learning. But just don't expect it to do the job for a CNC cutter. Many of those type units don't even hold up to extended hand use, they are really designed for occasional light duty use, and anything more than that takes them out in short order. Built down to a price.

[everlastsupport]

Two most important things Rambozo mentioned. Duty cycle on a low end cutter, it will die. They are made for small/short hand cuts. Second, HF start (you could tap it and run into the cut I guess)... You need a better plasma cutter for CNC.

Far as Pi and BBB, great idea since they have a lot more RAM (no pun). The atmel and pics are probably fast enough, but limited on memory.

[EmptyNester]

Hi Guys,
Ive purchased a cheap ebay plasma Cut50, i had no choice - down to cost and demand.
Im wanting to incorporate the Arduino THC which leaves me with a couple of questions.
the voltage measurement is it taken from the torch and earth clamp connectors and i would be expecting to get something like 200v to 300v.
my other question is more of a request really.

And just to show my ignorance i have a real newby question.
i dont have a clue what plasma ive bought:-
i think its a HF one with no pilot start as i have to make contact with the work piece before it arcs

look forward to any feedback or suggestions.

Jason,

I went through extensive web and product searches trying to do this as economically as possible (it's a hobby for me rather than a business). Ultimately, I ended up with an Everlast Power Plasma 50 for a number of reasons:

• pilot arc start
• CNC port
• user feedback on the machine
• user feedback on support from Everlast

I would not expect that you'd be able to use the THC design for a number of reasons:

• the noise of HF start would probably be too difficult to overcome in a home built system
• the high voltage input (100 to 120 volts) is based on a voltage divided input that's a pretty clean signal (I would expect that there's a good chance the THC would be fried if connected to the full/raw torch voltage)
• there is no stepper driver interface to drive the Z-axis
• the THC doesn't know the height of the object being cut, so you could end up crashing the torch head badly (that's why integration with Mach is important)

I would have to strongly advise you not to try to use this design. It would probably be pretty frustrating and not work. It might be reasonable to use as a starting point, but I expect you'd need to redesign the voltage sensing and filtering circuit. Having done this one and know the work involved, I personally wouldn't try to undertake it.

Disclaimer: I'm not an employee or compensated in any way from Everlast. I'm just a customer who's very happy with my products from them and the experience I've had dealing with them.

[meJasonT]

Hi Guys
Thanks Emptynester, Rambozo and Mike R for your feedback.
oh poop, now im left with a cheap Chinese machine and not a hope in hell.

I didn't mention in my last post that i had a parallel breakout board available for using mach3, but being anal i wanted to use GRBL as its so simple (http://zapmaker.org/projects/grbl-controller-3-0/).

so it looks like i will go for the tried and tested method of arduino THC and Mach3 that you very kind gents have debugged and got working for us mere mortals.
it sounds like a good plan to get it up and running on the cheapy machine before going to the expense of a pro machine.
there is a youtube video out there where a Russian dood has got a cut50 working on a CNC, so im not planning to give up just yet.
The plasma will probably do about 20 hours work over a year, so im foolishly optimistic that there will be some life in the old girl.

I wish id joined the forum before buying the plasma now.
to think three years ago i had the chance of an old CIP machine

ive made a really nice CNC table if nothing else, i will post a picture.

cheers
Jason

[none]

Hi,

Im sorry I didn't even realize that I've got answer from emptynester as the forum didn't send me notification of new post/reply. I don't know why it was set.
First of all thanks for the answer but I have further questions if you don't mind.
Here is a screenshot of the windows program but I couldn't figure out where I can set up the pierce delay and pierce height. Where and how should I set it up if I can't in the windows interface?
Unfortunately there is not much of this windows control program in the user manual.

Many thanks

[Rambozo]

Pierce height and delay are typically set directly in the g code sent to the control. The settings should be in your CAM software, or can be done with hand written g code. The THC does not take over control until the OK to move signal is set. Also your control may do a touch off to calibrate pierce height before each pierce. LinuxCNC can use an m code for that, and I believe Mach does as well via the touch probe input and G31. That really helps to get things in the ball park if you have material that isn't very flat, or you change thickness of material.