Help me tune my THC

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yroc fab
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Help me tune my THC

Post by yroc fab » Fri Apr 14, 2017 1:14 am

I have 5x10 Precision plasma table with Candcnc electronics, hypertherm 85. I have had it running great since last june Except for the DTHC. Ever since the first cut i have kept the thc off and not bothered with it since im usually doing small one off parts. Lately I have been doing production runs of 2'x2' parts and could really benefit from it so i figured its time to reach out and ask for help.

I have kept it off because the few times i have tried using it has crash the machine. When cutting with it on it will fire the torch and start cutting and dive the torch down into the material. I have turned it on after it has established the arc and is in the process of cutting and watched it work just like it is suppose to. Its just the starts that seam to be my problem. I don't think it my voltage reading because they seam to be on key with my preset hyperthem toolsets recommended voltages.

My table build thread> ... highlight=

Any input is much appreciated.


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Re: Help me tune my THC

Post by ovrrdrive » Fri Apr 14, 2017 7:07 am

By chance did you disable the tip saver and enable VAD?

Those two settings were why mine weren't working. I fought mine for a few months too and finally took the manual and went through page by page in the DTHC setup and wrote down all of the results of the tests and posted on the CandCNC support forum and that was what they came up with and what ended up fixing my setup. I'll see if I can dig up a link to the post I made that helped.

Just make sure if you ask for help there you have run all of the tests in the latest version of the manual. ... php?t=1591

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Re: Help me tune my THC

Post by motoguy » Fri Apr 14, 2017 8:50 am

What is the THC delay setting? Sounds like it isn't long enough, and is kicking on before the arc stabilizes. You can also use "distance for thc" (or something like that) to set a minimum distance the torch must travel before THC kicks on. Helpful for piercing, and features where you do not want THC active (such as holes).
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Re: Help me tune my THC

Post by acourtjester » Fri Apr 14, 2017 10:27 am

here is the start delay motorguy is talking about, use about 1.5 seconds

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Re: Help me tune my THC

Post by tcaudle » Fri Apr 14, 2017 11:54 am

Several things have to happen when the torch pierces and then the DTHC turns on.
1. The touch off sequence HAS to be correct. The torch needs to rise up and fire at the right height then plunge, start the cut on THEN the DTHC turns on after allof the drama of the pierce and resulting voltage spikes are gone.
2. The Plunge rate (set in SheetCAM) has to be fast enough to keep from blowing a big hole in the metal. Plunge time is part of the Pierce delay. The Rate should be close tot he max velocity you have for Z to minimize the time .
3. The STHC Delay in the toolsettins needs to be long enough that it does not turn on DURING the first second after the startof the CUT (not the pierce)

The POST does not turn on the DTHC until it hits the Cut height (that HAS to be lower than the pierce Height) and then the DTHC Delay time starts. Defautl value is 1 sec which should give it time .

If you are cutting small objects/circles you should use the "Min Cut Lenght for DTHC" option in the SheetCAM operations. Use a value that is greater than your the total length of the cut plus the lead-in. It just leaves the DTHC off on short/small cuts.

Since the answer depends on the system you have (Windows or LINUX) it helps to have a profile of the equipment. The DTHC works in the same way but has some other features in CommandCNC

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