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Hi all
I'm looking at upgrading to include a THC, I've found this one at a price within my budget.
proma-elektronika.com/index.php/en/products/thc.../compact-thc-150

Does anyone have any experience of this with LinuxCNC and a home grown plasma table?

Are they easy to install or will I need another budget for more kit and a degree in who-knows-what?
Any thoughts comments greatly appreciated.

Cheers

Danny

I built my plasma table and currently use Mesa 5i25/7i76 with the THCAD card. Cost about the same as your up/down THC and includes the motion control cards with I/O.

JT

Tom,

I am setting up my homebuilt CNC (in Scotland) using a proma-elektronika DTHC and am using your config files, with pins changed to match my setup. Test mode on Proma gives the correct UP, DOWN, and ARC OK signals visible in Linuxcnc. I can't get the system out of ESTOP; the ESTOP connections are spread across two separate .hal files and I'm not sure how to configure them. The pin is correct as tested with a different config for the same machine. Halfiles attached - can you help me with this?


Andy

My bad, I had uncommented some estop-related things and when I returned them to the same as in the downloaded .hal files it worked ok. Now wrestling with trivkins vs gantrykins - my machine's happy on trivkins in another configuration. Can't get the axes to jog at the moment.

a

Hi, I am also trying this config, and so far it seems to be working, but I am encountering something weird.

Every time I execute the M3 command, the system finds the work piece and sends the Torch on signal, but as soon as the plasma sends the Arc OK signal the Estop is triggered for some unknown reason.

I do not know if it could be that I inverted my Arc OK signal and I now need to invert something else.


Thanks
Jacob

groblerjf@gmail.com wrote:

Every time I execute the M3 command, the system finds the work piece and sends the Torch on signal, but as soon as the plasma sends the Arc OK signal the Estop is triggered for some unknown reason.

Is there any error message, such as a limit-switch trip?

It might well be electrical noise.

Could you attach your current HAL file so we can see if there are any inputs that might be picking up noise to cause this?

There are no error messages that pop up.

Other than changing the pins, and inverting some of the signals nothing else was changed from the files I downloaded.

I did try it again, same result. However I may been wrong in describing that the Estop is triggered, because the Estop button on the interface is not depressed. To allow motion however, I have to press the Power button.

Thanks

OK., that is quite a config isn't it?

I would guess there is something funny going on with the inputs to estop-latch.

Perhaps it would help to get a graphical view of the HAL wiring?

wiki.linuxcnc.org/cgi-bin/wiki.pl?Rockhopper_Web_Server

(I have never used that, but I have heard it can help)

Hi

The problem you describe is exlusively related to High Voltage/High Frequency start systems in plasma cutters, so Andy was right regarding the electrical problem.

There are solutions for this as noted below:

Cabling

---

the torch and ground cable from plasma should not be parallel with other cabling -NEVER EVER- exept when using high quaity RF shielded cabling.

The limit switch used for finding the work piece

---

it has to be configured and connected as NC or normaly closed. This for a simple reason: it stays always connected to ground exept when triggered by touching the work piece so when the torch starts it is at ground potencial and way less prone to RF interference.

Plasma cutter

---

as far as posible from everything else. This is limited by the length of the torch cable, but having the computer and electronics on one side of the machine and the plasma cutter on the other helps a lot.

BOB

---

This is more complicated to fix and requires some soldering skills and 5 220 - 330 ohm resistors. The resistors have to be soldered to 5 inputs on the BOB and to +5V so it keps them pulled up all the time until there is a signal on the inputs.

That is it.

I have done this several times ( over 15 ) on a wide range of CNC plasma cutters and this is the exact procedure that i use and it always works, always.
There are also High Voltage start plasma cutters and they cause much less troubles, and scratch start, but the latter is not usable for cnc.

regards
Tom

Ok, so the system I am running is a Powermax 45 with machine torch.

So I implemented the solution you suggested Tom.

- I rewired the limit switch so that it is normally closed. I installed a pull up resistor on the 5 inputs.
- The plasma cutter is as far as possible fom the PC.
- The cutting torch cable and the ground cable of the plasma cutter is on the opposite side of the control cables as well.
- The only cable that runs next to the other cables is the pc interface cable that is connected to the plasma power supply.


I have not yet tried the online diagnostics tool as Andy suggested as my PC is not connected to the internet. I did however discover that it is indeed the float switch that is causing the problem. I used a standard mill config and just arced the torch. If a z limit is defined during configuration then an Estop is triggered, but when that same pin is set as unused, then the system arc's and I can cut further.

Any suggestion on how to fix this.

My z float is just two wires dangling next to the machine torch, should I perhaps just install shielded wire and see if that does not fix the problem.




Thanks
Jacob

It is absolutely necesary to use shielded cables in your case, you can use even RG 58 or RG59 tv antena or video camera or audio cable with one wire in the midle and one as a shield. Just connect the shield to the ground on your bob and the midle wire to the input.

I also forgot to mention one of the common errors i have seen around : stop grounding everything at the same point. That is o.k. for other machines, but it can be fatal on plasma cutters. I have explained that in this forum and some others so i won't repeat myself, just to prove a point : almost all power supplyes have ground connected to minus terminal internaly as it is supoesed to be but the plasma cutter clamp that is usualy clamped to the material or the ribs on the cnc is the positive.
Tom

Do a test an wrap the limit switch with alu foil properly, afetr you change the wire. If the switch is close to the torch that will help a lot.

Thanks, will do it in the morning.

Regards
Jacob

Another thing that can help is debouncing the input signals with the hal debounce component

Hi, so I did not wrap the wire in Al foil, but I did add a shielded cable, not sure whether it helped, may have installed it wrong. What I did do is debounce the float switch electrically with a 100nF across the switch, I went one step further however and installed and opto-coupler. I also rewired the switch to be normally open.

There is a new problem however. For some reason now, as soon as the arc establishes, and motion begins, the machine moves extremely slow and I have no idea why. Everything works fine, even my own implementation of THC, and normal motion is at the correct speed, but when I issue the M3 command, the motion is extremely slow.

Attached is my thc_toma.ini file

Any ideas???

Regards
Jacob