Kerf Settings with inner cuts

Hi Guys,

I’ve recently purchased a 1390 130 Watt Laser and have been trying various things.

I don’t know if this is intentional in the software or a bug, but can someone explain how the kerf settings work in Lightburn?

Scenario 1: Rectangular cut.
I did a test cut on a piece that is 50mmx75mm, I figured my kerf to be 0.12mm.

Scenario 2: Finger joint
I cut a 20mmx30mm with a finger joint for my 4mm acrylic material and a 4mmx8mm slot in the middle of the 20mmx30mm piece.

Case 1: Rdworks
I used RD works to set the kerf on my laser, which I figured to be 0.12mm.
I would set the Sew Compensation to 0.12mm and I get a perfect cut.
I get the exact dimensions for both scenarios 1 and 2, and the finger joint fit snug together.

Case 2: Lightburn
Scenario 1:
If I set the kerf to 0.12mm, my Rectangle would come out smaller.
Setting my kerf to -0.12mm, my rectangle would be perfect.
Scenario 2:
If I set my kerf to 0.12mm, my finger and joint would be a snug fit.
Setting my kerf to -0.12mm, my finger and joints don’t fit.

TLDR: If I only have a single outside path to cut, the my kerf would be -0.12mm, but if there is an inner part, then I would have to change my kerf setting to 0.12mm.

I didn’t have to do that in RDWorks

LightBurn automatically detects whether an object is inside or outside something else, and offsets accordingly. Positive numbers move outward from the shape, negative numbers move inward from it.

In #1, was the rectangle the only thing in the project? Or was it enclosed by another shape?

#1 was a rectangle by itself, I had to set the kerf to negative for it to cut correctly.

Acted as though it’s an inside shape

Did you make the rectangle in LightBurn, or was it imported from somewhere? Can you post the file so I can take a look?

It was made in lightburn.

it was a simple 50mm wide by 75mm tall rectangle.

The finger test file I made in illustrator though, and the kerf settings came out perfect on that.

I also noticed, if I have other objects together with ones that have a finger cut, then the kerf settings come out good. It’s just when you have only object on the drawing board and none of them have an inner part that the kerf seems to be effected.

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