THC Problem - Linux/THCAD10/SheetCam

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02 May 2021 22:23 - 02 May 2021 22:43 #207687 by RNJFAB
Hey All,

Now everything running I'm having a few issues I would like to fix and need some guidance.

1st issue - from time to time, when cutting the Z axis will dive down and trigger the probe sensor. I'm guessing that its trying to get the voltage high and is diving to try and make this happen.

2nd issue - diving on corners. I know this can be adjusted in the settings or post processor. I just don't know how. these are my current settings.

3rd issue - PNP sensors on the limit switches trip out. I know I need some sort of debouncing in the Hal file, I just don't know what this looks like or how to do it. If someone has the lines of code for this can you post it please.


Link to my build with most details.
forum.linuxcnc.org/show-your-stuff/42411...ade-cheap-plasma-cnc
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Last edit: 02 May 2021 22:43 by RNJFAB.

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02 May 2021 22:50 #207690 by tommylight
Height per volt seems wrong, default is 1 and it should work just fine.
Diving issue, do you have corner lock on and at what percentage ?
If the sensors are tripping at torch fire, no amount of debounce will help. That will be grounding/shielding issue and has to be dealt with before ending up with something in smoke, besides the cutting smoke.
If they trip during homing, debounce helps so have a look at the existing machine config there are some debounces there so just add as much as you need and connect them to sensors in hal.
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03 May 2021 08:01 #207707 by robertspark
issue 1, you have it the wrong way around
torch will dive to lower the voltage, the voltage gets bigger when the gap gets wider. that is why when the torch slows, the kerf gets wider, the voltage gets higher and with thc the torch dives to LOWER the voltage sensed
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03 May 2021 09:27 #207710 by robertspark
issue 3, could be a few things. what plasma cutter are you using (make, model, link?)
how have you wired your proximity sensors?
(sketch the circuit please)

how much load do you have on the sensors, do they feed directly to an input pin. the impedance of the Mesa input pins on 7i76 is about 20k


automation-insights.blog/wp-content/uplo...-768x1000_update.jpg
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09 May 2021 00:32 #208348 by RNJFAB
Thanks Tommylight,

I'll change the heigh per volt now.
corner lock on 99%.

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09 May 2021 00:33 #208349 by RNJFAB
Thanks Robertspark,

I'll try adjusting the set voltage to a higher voltage.

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09 May 2021 11:33 #208363 by tommylight
I leave corner lock at 60 to 80%.
Height per volt is roughly 0.1, i think RodW came to that conclusion from his extensive testing.

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11 May 2021 12:49 #208542 by RNJFAB
Thanks Guys,

Settings changed, works great.

However tonight I cut some parts from ally, all went well with new settings, then boop, no more torch fire. can't get the board to fire the torch. tried resetting and using the pulse button in the GUI. NOTHING. every now and then the board will light up to say it has turned the torch on, and the relay will light up, but no spark.

Any ideas?

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11 May 2021 13:00 #208543 by tommylight
-Dirty nozzle/electrode
-loose electrode
-not enough air pressure
-to much air pressure
-faulty pilot arc circuit (if pilot arc start)
-faulty current limiting (if blow back start)

Is it inverter or transformer type?
On transformer types there is a distinct laud "click" when the big relay inside engages, turn off the compressor and listen for that click.
On inverter types the only outside noticeable sound is the fan changing (lowering) speed by just a bit (more noticeable in US than Europe) when firing.
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11 May 2021 20:53 #208582 by RNJFAB
changed nozzle/electrode (first thought)
all tight
60psi

Plasma will start (pilot arc) if I short out the start circuit.

MESA board will light up to say that the torch should be on (sometimes), relay will trigger to tell the plasma to start, plasma will try and fire then stop. then mesa will stop triggering the relay.

Tried changing relays, restarted the system several times, changed wires, etc.

No errors in LinuxCNC.

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