FireControl THC On/Off using SheetCam

Hey guys…I was reading the information on FireControl on the website and I think I am understanding this right as far as FireControl turning the THC On/Off. It says you can put a percentage factor (example they have is 85%) that when the speed drops below it will turn the THC off then after the speed increases it will turn the THC back on. I am just wondering since they have that setup in FireControl then I do not have to worry about putting a code snippet in SheetCam to turn the THC Off/On do I? Or if I had the code snippet in SheetCam to turn it Off/On would it conflict with FireControl and have any issues?

I believe they said they will provide a Sheetcam post, so if it’s need or not, the post should do it.

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The Sheetcam post will configure the code precisely how is needed to run on the CrossFire PRO with THC. To answer your question, there are codes in it that give control of the Z driver to the THC controller and also restore control to the motion controller.

The THC controller has the ability to ‘sniff’ the X and Y step pulses sent by the motion control board so it has an extremely accurate reading of Torch speed at every instant. If the measured torch speed drops below a threshold (85% of programmed feed rate is default), the THC will stop making corrective moves. This is known as ‘anti-dive’ and is important for making sure that the torch doesn’t drive into the plate for features like sharp corners and holes.

If a dive were to occur and the torch touches the plate enough for the IHS switch to open, the THC will cease to make corrective moves and instead will move back up to cutting height before resuming corrective moves based on arc voltage.


Hey Daniel I appreciate the info. I have never used the THC before and excited to get it with the new table so I have tried to read up on it as much as possible. I was just wondering That since SheetCam has the ability to set up the same parameters of shutting the THC off and on according to speeds I set for corners and circles and such. Would it be better to set up the post processing from SheetCam to turn it off on at the speeds or just let Firecontrol operate the THC off and on according to the speeds? I hope I’m making sense of what I am trying to ask. I just don’t want to double up on that function and something go wrong. I would rather just be able to set the speeds in SheetCam and let Firecontrol work the THC. Don’t want to have to set it up each time in SheetCam if I don’t have to.

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Good question. I was wondering the same thing.

So if I setup a SheetCam rule to slow and turn off THC for sharp corners (Similar to what is done in the SheetCam tutorials), I would leave Fire Control’s default 85% threshold?


You don’t want to set up any path rules in Sheetcam. Path rules are used with standalone THC units where you don’t have torch velocity feedback and need a way to estimate whether torch will slow down enough to cause diving to happen.

The CrossFire PRO has an integrated THC with speed feedback, rendering path rules entirely unnecessary.


Thanks Daniel for explaining. Looking forward to running this machine!

Thanks for the information Daniel!

I was skimming this post hoping to verify the G code that turns the THC on/off so I could set-up path rules, but based on your comment above sounds like that should not be done.

I wanted to try some path rules because I am getting severe bevels on sides with multiple corners and in circles, no matter how I orientate the part the bevel and poor cut quality are always in the same portion of the part so it isn’t an alignment issue with my table or torch.

I have tried changing out my consumables and adjusting my cut height, neither made a difference. If there is a turn on one side then I get a terrible bevel on that side and the finish looks like the torch is trailing. This tells me something needs adjusting in my software/post processing etc.

So, any idea what my problem is?

I was having similar issues on the original crossfire. We started using sheetcam and created rules to slow down for tight corners etc. and that solved our issues. I can’t absolutely say that’s your problem here but it’s a possibility. Once we upgraded to the Pro, we have continued to use the rules we created but like what was said earlier didn’t add any THC on/off options. They have continued to work to this point.
Some parts/art I will also use the finecut slow speed settings to make sure the machine isn’t turning too quickly and losing the fine lines and corners. This could be something to adjust also depending on whether you’re using finecut consumables.

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So you are able to use path rules with the Crossfire Pro with THC, you just don’t program any THC on/off?

What plasma cutter are you using?

I am using a primeweld cut 60 machine. The cut shown is 1/4" mild steel cut at 45 amps and 37 ipm, using a 60 amp nozzle, thought I do have a 40 and 50 amp I can try.

Thanks for the feedback.

Yes I’m using path rules but no THC options selected.
I’m using a Hypertherm 45
unfortunately I don’t have enough experience to suggest changing amps or nozzles that way.
I know my speeds for 1/4 with a regular nozzle is around 40 ipm. It just looks like the plasma arc isn’t cutting completely straight down at those angles so slowing it down allows it to ‘keep up’ from trailing behind. There are definitely others who may chime in who have tons more experience here but I’d add path rules to slow down or slow down the overall speed and see what happens.

Part of Langmuir’s THC control is they turn it off when going through corners. If you go back to the THC Manual you’ll see there’s actually a setting in FireControl to set the tolerance it will use in determining when to shut the THC off.

The rules are simply slowing the speed down during curves and tight corners. Independent of what the THC is doing.
A fix for beveled curves/corners or rounded edges that should be sharper is to slow the machine down as it is turning. Nothing to do with THC, as I’m assuming the torch height is either fixed or the THC is working as it should.
The way I understand it anyway, is with other machines if you don’t turn the TCH off during tight curves and corners it will lose voltage and dive. Most machines thus have the TCH on/off commands needed with these types of rules. Langmuir prevents this by programming in Firecontrol instead of having to program the G-code.

Exactly! :slight_smile: