What command is used for THC and IHS

What commands are used to turn on THC and IHS. I have a post processor that seems to work but I want to integrate the THC and IHS into my program. Does anyone know how to do this or has done it before?

This is the set of commands for the IHS loop.

G92 Z0.
G38.2 Z-5.0 F100.0
G38.4 Z0.5 F20.0
G92 Z0.0
G0 Z0.02 (IHS Backlash)

I don’t see any commands to turn the THC on and off in the code. I think that is strictly controlled by Firecontrol software.

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Thank you for the response. Does this get placed in the post processor before each cut?

Yes. It goes before each cut loop. There are actually two more lines in the loop, before the torch fire command. This is my understanding of the code:

G92 Z0. (sets Z zero)
G38.2 Z-5.0 F100.0 (probes downward 5" until the switch opens and stops- rapid speed 100ipm)
G38.4 Z0.5 F20.0 (probes upward until the switch closes and stops - rapid speed 20ipm)
G92 Z0.0 (sets current location as Z zero)
G0 Z0.02 (IHS Backlash) (adds .02" to Z zero location to account for backlash)
G92 Z0.0 (sets the current location as Z zero)
G0 Z0.14 (Pierce Height) (moves Z to pierce height)

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IIRC there were H1 and H0 commands to turn on/off THC, but that may be older version of FireControl.

For more insight, take a look at the SheetCam postprocessor for FireControl. It’s pretty readable.

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I think you are correct. I see an H1 command after the torch lowers to cut height and and H0 command at the completion of each loop, just before the torch off command. I assume they are using these commands as H1(THC on) and H0(THC off).

Here is a whole cut loop from one of my recent files:

G92 Z0.(set Z zero)
G38.2 Z-5.0 F100.0(probe downward until switch opens-rapid speed 100ipm)
G38.4 Z0.5 F20.0(probe upward until switch closes - rapid speed 20 ipm)
G92 Z0.0(set current location as Z zero)
G0 Z0.02 (IHS Backlash)(add .02" to current Z to account for backlash)
G92 Z0.0(set current location as Z zero)
G0 Z0.14 (Pierce Height)(move to pierce height .14")
M3(torch on)
G4 P0.4(pierce delay .4 seconds)
G1 Z0.05 F100.0 (Cut Height)(move to cut height of .05"- plunge rate 100ipm)
H1(THC on)
G1 F100.0(program speed 100ipm)
G3 X5.9751 Y11.8566 I0.0734 J0.1049 F60.0 (these 7 lines are coordinates for the cut loop)
G1 X6.088 Y12.0178
G1 X6.3428 Y12.3817 F100.0
G1 X5.7758 Y14.8978
G1 X5.4961 Y14.6657
G1 X5.6397 Y11.3775
G1 X5.9751 Y11.8566
H0(THC off)
M5(torch off)
G4 P0.5(this is a pause I have set for .5 seconds after each loop)
G0 Z1.0(raise Z axis to 1" clearance height)
G0 X7.5028 Y11.2059(move to next cut loop starting location)

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The only other important piece for THC control in posts is the PS value comment at the end of the file. This is what FC sends to THC as the program speed and used for turning off THC when the torch isn’t moving at speed- in corners or tight radiuses. Most plasma programs only use one feed speed and this value should be placed in a comment on the last line of the program as:


for 100 IPM
These numbers should also match the G20/G21 units of the file.


I am having problems adding this to the post processor. How does it need to be inserted? Should everything be in quotation like this for example? or is there another way to write it in?

“G92 Z0” .(set Z zero)
“G38.2 Z-5.0 F100.0” (probe downward until switch opens-rapid speed 100ipm)
“G38.4 Z0.5 F20.0” (probe upward until switch closes - rapid speed 20 ipm)

Everything in parenthesis is comments that I added to explain what the command does. They do not need to be in the code. The text in quotes should not be in quotes in the code. The letter needs to be the first character in the line. I’m not great with code, but I’m pretty sure quotation marks are used to tell the computer to ignore that line.

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