Kerf takes affect in preview, but not on the machine

I have a footfile that I have drawn and imported as I have done with many files before. I have applied the Kerf amount in the layer properties. If I exaggerate the kerf I can see the kerf taking affect in the laser cut preview screen. However when I run the cut, the Kerf makes no difference to the actual material and still undercuts. I normally set 0.1 to 0.15 for 4mm acrylic, however even if I make it 1.0 I don’t see a change in the cutting result. I am measuring with a Vernier. If I import another file with just a 40x40mm square and apply the kerf, everything works as expected. Its just this one file that doesn’t work for me as expected. Could someone take a look and see if I missed something? I checked for line joins, checked it was single polyline, looked for gaps etc etc. I have attached the file. Thx in advance.
Test File.lbrn2 (256.0 KB)

Are you having an issue only with the outside kerf?

I don’t see any issue in the design. The preview clearly reacts to kerf size changes and in comparing g-code exports I can see that the kerf is being respected and included in the actual cut path.

Likely something else going on. How are you testing this? Are you saying no matter the size of the kerf there’s absolutely no change in measurement?

Yes, the inside Kerf for the hole is changing according to my Kerf settings, but the outside Kerf doesn’t change. I changed the Kerf on the outside, then cut a paddle, measured, changed the kerf larger and measured again. Each time the outside measurement had not changed when measuring the cut piece.

I upload the code to the machine through the computer, overwrite the existing file before proceeding with the cut. I even tried deleting all files, change files names etc in case of confusion.

Is there a way to get the compiled file out of the machine and check it? or maybe I should redraw from scratch and test again… If its just this one file that I did a work around by editing the actual drawing, not sure its worth investigating further unless you think there may be a glitch?

You could try saving the .RD file and load it back into LightBurn. I’ve done this and I can clearly see a change in size.

Here’s a screenshot of 2 overlayed. One is at .2mm and the other at 5mm kerf:

Did you remove absolutely all files from the controller when you did then?


Maybe a clarification of what you are doing.

A kerf that large sounds like you are ‘hacking’ to get some other results other than it’s intended use.

Generally you use kerf to allow parts to fit properly, 5mm exceeds what I’ve seen, assuming it’s a laser and not a 10mm mill end.


Yes, removed all the files and uploaded from scratch. I did the same as you did by exaggerating the kerf in my tests with no change in the machines behaviour when cutting.

No. I was only using that large a kerf to make any changes apparent since the stated symptom was that no changes resulted from modifications to kerf value.

Can you do the .RD file save and compare test. Curious if the issue is in the file generation or somewhere else.

If that works, can you try saving to USB and running it that way. May help isolate the issue.

Super swamped at the moment, will try and get this test done in the next few days.

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