THC cannot keep up

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28 Apr 2022 19:58 #241561 by Jalapeno56
I officially have 34 tabs open researching a fix.....
Debian 11 with 5.10.0-13-rt-amd64 kernel
Lcnc 2.9.0 with QTplasmac 1.223.184
Cut starts good, THC raises and locks causing a bad cut, and THC will dive tripping the float sensor all on the same cut.  Material is relatively flat.  Velocity A/Dive or Void A/dive on or off doesn't matter.  Using autovolts.  I have attached a screenshot of my current settings, a backup of my configs and a copy of the gcode (it has strange ripples on the sides of some letters, they are a problem with the source file.)
I feel like I have tried everything, but as always, its some setting I have missed!  The Z axis does move 1" when Lcnc says it moved 1".  I also re-visited latency and MAX-ACCEL/VEL and only made minor changes with no real solution.
Things you cant see: Hypertherm 45xp running at 45 amps, 72psi of air cutting 14 gauge mild steel.  2.8 lbs. of force to move floating head upward (checked thinking maybe the air was forcing the head up).
Any help is much appreciated!

 
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28 Apr 2022 20:04 - 28 Apr 2022 20:06 #241562 by snowgoer540
Replied by snowgoer540 on topic THC cannot keep up
Away from my pc so I can’t look currently but I see the backup is from 1.221.144. Can you make a recent one and post it please?
Last edit: 28 Apr 2022 20:06 by snowgoer540.

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28 Apr 2022 20:35 #241565 by Jalapeno56
Replied by Jalapeno56 on topic THC cannot keep up
I remember something about the header not showing the current version of QTplasmac and i just updated, 2 minutes ago, but still cannot find where to find my current version. Thought it was "man QTplasmac" in a terminal window but that does not work. and of course you cant google "what is my qtplasmac vesion" and get a real answer.

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28 Apr 2022 20:35 #241566 by rodw
Replied by rodw on topic THC cannot keep up
A couple of observations
1, Antidive threshold is 68%, should be 95-99%. It will probably never be activated
2, THC delay = 0. By the manual, this means as soon as arcok is received the voltage is sampled and thc activated. At this point, the arc voltage will be very high during the pierce. The auto sampled volts will be way wrong. Change the thc delay to 1 second and see how you go.  If the problem persists, try 2 seconds.If the problem is still there, look further afield.

1 second  is probably a lot longer than required but the intent is to get you cutting and you can reduce it later. Maybe to 0.3 seconds but somebody with a 45xp might have a better idea.

It is always very informative to use halscope and plot arc voltage, torch on and arcok during a pierce with THC disabled and enabled because then you can see what is going on and set a delay to suit your environment.
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28 Apr 2022 21:05 #241568 by tommylight
Replied by tommylight on topic THC cannot keep up
You should really set everything back to default, to much of strange values there.
As a general rule:
-Disable VAD
-Disable Void ...
-Do not use auto volts
-leave everything at default, except the float travel, pierce height and probe height, leave all delays at 0
-adjust the voltage till the machine cuts properly and follows the material
Only then try with auto volts, and for that a general rule:
-pierce delay should not be longer than THC delay
-pierce delay should be enough to get consistent piercing and start of the cut, for thin material, 0.1 to 0.3s
-THC delay should roughly be 50 to 100% more than pierce delay, so 0.15 to 0.45 for thin material
--Thin material is 1 to 6mm, even 10mm are thin if using a 200A plasma, so the only sure way of finding out is doing a lot of testing.
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Why is the voltage set to 72V ? Do you have the scaling and offset for the Mesa THCAD set correctly? Voltage should be from 92 to 135V, depending on plasma source, torch/nozzle used, material, humidity, etc.
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And since i just read the replies, Rod, antidive at 95 to 99% is useless for anything but straight lines!
I have it at 65 to 75% always, on all machines, over 20 of them, depending on the acceleration the machine can handle.
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28 Apr 2022 21:14 - 28 Apr 2022 21:34 #241570 by snowgoer540
Replied by snowgoer540 on topic THC cannot keep up

I remember something about the header not showing the current version of QTplasmac and i just updated, 2 minutes ago, but still cannot find where to find my current version. Thought it was "man QTplasmac" in a terminal window but that does not work. and of course you cant google "what is my qtplasmac vesion" and get a real answer.


As far as I know there has never been an issue with the version in the header. It's populated at run time, so if it shows 1.221.144, then that's the version you are running. It's also populated again when you click to make a backup of your config. Perhaps you can't google, but it is covered in the manual: linuxcnc.org/docs/devel/html/plasma/qtpl...tml#_using_qtplasmac And the backup decode info is just above this section here: linuxcnc.org/docs/devel/html/plasma/qtpl...ml#qt_statistics-tab

I don't mean to question you, but are you sure you are on Debian 11? To my knowledge package installations are not supported in Debian 11. You are using a package install, as per the symlink in your config folder. It points to: /usr/share/doc/linuxcnc/examples/sample-configs/by_machine/qtplasmac/qtplasmac/

I would suspect that in your synaptic package manager, the repos are not pointed to Buster.

If you really are on Debian 11 (Bullseye), then to get the latest version you need to remove the package install, and follow the instructions to build from source. linuxcnc.org/docs/devel/html/code/building-linuxcnc.html


All that aside, in addition to what Rod (EDIT: and Tommy :)) pointed out, I have some other observations about your config:

1. Your setup speed for the Z axis is 600 inches per minute which is really fast. I run mine at 300 inches per minute, and even that's probably faster than it needs to be.
2. Compound that with having the PID P value at 25, and the I and D values at 10, and it seems like you would be doing a lot of over correcting. To Rod's point, HAL plots of the voltage with the Z position would be helpful to see if it is continually over correcting.
3. I see you made a material for 14 gauge material, but your cut file doesnt call it. Also, the Cut height, Pierce height, Cut feed, Pierce delay, etc do not follow the cut charts for a hypertherm 45xp.
4. For the default material, your pierce height is 0.060 and your cut height is 0.110. That is really high for a cut height. For Hypertherms, the pierce height is generally 0.120 and the cut height 0.060. Also the pierce delay is 0.8 seconds which seems quite long for 14 gauge. (I am not sure which material is getting used for the cut)
5. Your cut file doesnt at all follow the convention QtPlasmaC is looking for (M3/M5 commands, and there are Z movements, etc). I know Tommy uses inkscape to make cut files, he may be able to point you to a post processer that is suited for this application.

That said, the program does simulate, but it runs with whatever material is selected. Which is fine, but as mentioned both materials have issues.
Last edit: 28 Apr 2022 21:34 by snowgoer540.
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28 Apr 2022 21:35 #241573 by Jalapeno56
Replied by Jalapeno56 on topic THC cannot keep up
Thank you for the replies fellas!
I remembered why I stopped using Halscope, no offense, it doesn't act like any scope i have ever used. No way to change volts per division..., and the values it does show (not on the graph) per division, what are they? mv, V, Kv?? ( I assume volts) The trigger doesn't work, and no way to see time scale on the graph. Or maybe I just don't know how to work it!!! I'll just T in a real scope and see what i can come up with.
Tommy:
I probably have my settings out in left field right now. I will take your suggestion and start from default. Volts of 72 came from Hypertherms recommended settings for 14 ga. They also recommended a cut height of .06, which doesnt even come close on my setup. I re-verified voltage scale (I was 0.7v off), no change in cut performance. Using a fine cut tip from hypertherm, The general usage tip was better but still not good. Will report back soon!
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28 Apr 2022 21:48 #241574 by tommylight
Replied by tommylight on topic THC cannot keep up
I use Inkscape (so do all the machines i maintain and service) so i did modify the Inkscape extensions to produce PlasmaC worthy gcode ! :)
I have the old and new versions of Inkscape, so i have the old and new modified files if anyone wants them.
Friendly warning, i have no idea for what version of Inkscape they are (hence the old and new terminology), so it might mess up Inkscape. Making a backup beforehand removes any risk and can be reverted back at any time.
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OK, seems a bit low at 72V, but i trust Hypertherm, they know their s#it! :)

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28 Apr 2022 21:49 #241575 by Jalapeno56
Replied by Jalapeno56 on topic THC cannot keep up
Thank you Snowgoer540! I will look at my build. It was a terrible journey as I am not real familiar with linux! So, I am not surprised that I have build issues. With all of your input, I think it may be time to take a step back and re-evaluate my setup from the core. And yes, I am using Debian 11. I couldn't get any of the packages to work so I tried it from scratch. Guess I have more to learn!!
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28 Apr 2022 22:22 #241578 by snowgoer540
Replied by snowgoer540 on topic THC cannot keep up
There are a myriad of opinions and links floating around here, but if you don't NEED Debian 11 due to some hardware compatibility issue, then I would recommend giving this a try:  forum.linuxcnc.org/9-installing-linuxcnc...red-toward-new-users

I created it with new users in mind, to be a visual step-by-step covering every click, as when I was a noob, I found the "multi lines of text" instructions to inevitably miss some step and leave me confused... 

Building LinuxCNC from source isn't something I'd recommend to a new user, much less one not super familiar with Linux, etc.  My recommendation would be to do the package install, which is covered in that document.  

Also, I hated HALscope too in the beginning.  You learn to ...tolerate... it :).  Definitely is a necessary evil.  

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