THC issues and other problems

I have calmed down from my last post on the THC problems of the past and did some more testing i Have found that setting my cut height at .060 in sheetcam or F360 in the post process and start the program with the plasma turned off the torch will and touch the metal go up to pierce height and then go to cut height and stop(because the plasma is off)at which time i can measure the cut height with feeler gauges and find it to be .080 ,.020 too high it does this in F360 also exactly the same difference i also say another post on here to check the Z Axis driver dip switch #2 to make sure it is in the down position and it is.I’m open for any ideas i’m thinking what ever is causing this it is in FC. Thanks

It is a very common thing lots of people just program a different cut height I including me. The .020 is automatically added to compensate slack or metal flex. It is the nature of the beast.

There are at least 2 programs on here one I did and one @ds690 I believe that will cycle your z axis and not fire the torch. I am not around my computer so I can’t repost the file. Should be able to search cut height test.

Hope this helps.

Thanks Yea if i set the cut height at .040 and then measure it it is at .060 in both Sheetcm and F360 i would like to find a fix for this cause i think this may have been part of the THC problems i had for the last 2 years.

The fix would be in my understanding one maybe edit the post processor or sheet cam and f360 may be where the issue is. The other and common edit your cut height. We have seen some have to adjust more or less.

Regarding the .020" difference, it’s hard coded into the post processor for Fusion. I’ve seen several ways that people will correct for this.

  1. Reduce your cut height by .020. Fusion will add the .020 back.

  2. Set your Springback to -.020. Set your cut height as desired.

  3. Modify the post processor to either remove the additional .020, or provide an entry to adjust the Backlash value.

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Yea I didn’t know this was happining until i tested and compared set cut height to actual cut height on a clean .250 plate to eliminate any flex because i have been having the torch with THC on to start raising for no reason in a cut until it lost voltage and stopped cutting and sometimes ruin the job.

Does this only happen with the cut height or does it affect pierce height as well?

If your speaking of the additional .020" from Fusion, it occurs with both the Cut Height and the Pierce Height.

I was, but I can’t reproduce this. The cut values I put the Post Process fields is what I see in the .nc file. No change.

Fusion 360 2.0.17954 x86_64 [Native]
Active Plan: Personal
macOS 14.1.2 (23B92) on MacBookPro15,2

Fusion doesn’t change the Cut Height or Pierce Height values. It changes where Z0 is at (+.020").

(2D Profile1)
G0 X0.7419 Y0.632
G92 Z0.
G38.2 Z-5. F100.
G38.4 Z0.5 F20.
G92 Z0.
G0 Z0. (IHS Springback + Backlash) <— Look here. Unmodified post will have G0 Z0.020
with springback set to 0
G92 Z0.
G0 Z0.15 (Pierce Height) <— As set in Fusion
G4 P0.9
G0 Z0.062 (Cut Height) <— As set in Fusion

Sorry if I misunderstood your question.

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I don’t think I’m getting that … or I’m deep in Friday mode and missing it lol

G90 G94

(Front Hanger)
G0 X-6.0505 Y4.6374
G92 Z0.
G38.2 Z-5. F100.
G38.4 Z0.5 F20.
G92 Z0.
G0 Z0.04 (IHS Springback + Backlash)
G92 Z0.
G0 Z0.15 (Pierce Height)
G4 P0.5
G0 Z0.04  (Cut Height)

This line is adding .040" to the Z zero.

G0 Z0.04 (IHS Springback + Backlash)

This line makes that new height Z zero.

G92 Z0


So your post above that says “you’ve seen several ways people will correct this”
… are those each one of the ways or 3 steps that need to all be done together?

3 Separate ways. Any of the 3 are capable of correcting Fusions’ unwanted adjustment.

Note - List item #2 should read “Springback to -0.040.” #1 assumes you have 0.0 entered for springback. #3 doesn’t care, as the additional .020 would be removed from the post processor.

Edit - Apparently too much going on. Item #2 was correct previously as -0.020"


Only cut height

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