THC Delay in material file

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10 Oct 2021 22:49 #222806 by CFE
Hi all,

We are wondering if it is possible to set or override the THC delay in a material  file ?

We cut a wide range of material thicknesses, and we have found that on thick (25mm) material we have to increase the THC delay in order for the arc to sufficiently stabilize and get a good voltage reading. If we could set the THC delay in the material file then that is something we don't have to change manually and avoids operator errors.

Cheers, Peter

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11 Oct 2021 11:31 #222844 by rodw
Replied by rodw on topic THC Delay in material file

linuxcnc.org/docs/devel/html/plasma/qtpl...qt_material-handling

Tommy, thats not helpful. He wants to change THC delay not Pierce delay for different materials. AS it stands, it can't be done.

Which leads me to a theory I have after observations after significantly upgrading my machine's acceleration.
Perhaps the THC delay is the wrong way to go about it.
Maybe we should be enabling the THC when it gets to cut speed or constant velocity.
The hypothesis is when the current velocity is below the cut speed and accelerating, the arc is unstable and it stabilises when it gets to speed.
But it seems Peter's experience disproves the hypothesis.
If the hypothesis was correct, a component could be written that varied the THC on delay based on cut velocity.
I don't think the guys developing the software have the ability to cut thick materials with their plasmas so they don't see some of these issues.

I can certainly see that adding a THC delay parameter to the materials file that overrode the default if present would be a useful feature.
I think also adding parameters for material and material thickness to the materials file would also be useful for future enhancements. 

 

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11 Oct 2021 11:44 #222848 by tommylight
I am sure there are some shortcuts that can be used in gcode like "TD=1.5" and similar, seen it here several times so i thought it would be there.
 

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24 Oct 2021 22:18 #224128 by CFE
Replied by CFE on topic THC Delay in material file
Hi all,

Tommy's idea would work for us, we can add something to our post processor to include a line like "TD=2" or similar. What is the proper format for that ? I can't seem to find anything in the user guide to that extent.

Cheers

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26 Oct 2021 09:10 #224359 by rodw
Replied by rodw on topic THC Delay in material file
I don't think there is a gcode option for thc delay. If there is it will documented.

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30 Oct 2021 23:14 - 31 Oct 2021 00:05 #224737 by snowgoer540

Hi all,

Tommy's idea would work for us, we can add something to our post processor to include a line like "TD=2" or similar. What is the proper format for that ? I can't seem to find anything in the user guide to that extent.

Cheers


Have you tried the latest version of QtPlasmac? Phill updated the component such that it now starts the THC delay timer after 99.9% of the cut velocity is achieved. This is more in line with what the big names *cough* hypertherm *cough* do.

This should be much more consistent between different material thicknesses now because the THC delay timer is dependent on achieving velocity rather than starting the THC timer after the pierce delay... In fact, depending on how stable your power source is, you could probably (and should probably) lower your THC Delay to .05s or 0.10s or maybe even 0s (testing required obviously). Also with this change came the ability to make THC delay changes to the tenth of a second.

It seems like this might negate the request to have a THC delay specified in the material settings.

EDIT: It was a bit ambiguous but the change was pushed 13 days ago with this commit: github.com/LinuxCNC/linuxcnc/commit/9486...171f45821da5aa4d4096

EDIT x2: I meant my post was ambiguous not the commit :laugh: so much for trying to be clear lol
Last edit: 31 Oct 2021 00:05 by snowgoer540.
The following user(s) said Thank You: tommylight

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31 Oct 2021 00:03 #224741 by rodw
Replied by rodw on topic THC Delay in material file


EDIT: It was a bit ambiguous but the change was pushed 13 days ago with this commit: github.com/LinuxCNC/linuxcnc/commit/9486...171f45821da5aa4d4096[/i]


I think this is a good change as it also allows for different acceleration rates between machines. I'm glad you mentioned it.

Monitoring with halcope will help understand behaviour and set a suitable delay.

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31 Oct 2021 20:06 #224789 by snowgoer540
Was doing other testing today. But pictured below is a graph where my THC Delay is set to 0s. You can see that the voltage is stable for about 50mS before the first time the THC became active.

I didnt have time to test on different thicknesses, but I would expect other thicknesses to follow suite.

In case it matters to anyone, this is with a Hypertherm Powermax 65XP

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31 Oct 2021 21:01 #224795 by rodw
Replied by rodw on topic THC Delay in material file
Looks good!
What thickness material?
Whats with the voltage spikes? Are you testing kerf crossing?

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