THC config that works.

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?

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

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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

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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

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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

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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

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.