Understanding Kerf Correctly

Hi all,
Just trying to understand how LB works with Kerf setting.
If i enter a kerf setting for the design below. I assume it applies to the entire design.
The suqare and circle will be applied out from from square and in on the inner circle.
As for the circle, it will applied out.
Am i understanding this correctly?


For kerf operations, 2 items are needed. Your square edge and the outer circle piece “share” the kerfs setting. When I make finger joints in 3 mm plywood with my standard K40, I like to use 0.075 mm kerf setting, it fits well so the items are tight and do not fall easily from each other.

What about the inner circle in the square? Does kerf move towards the inside of that circle?
I m only using one layer.

You can make a small test, square and circle of the same diameter, e.g. 50x50 and ø50.
For “normal” construction I will adapt the required measure and not use kerf.

But if i need precise measurement in my project, i need LB to know my laser’s kerf.

in my example above, the square with the circle inside. I need my square to be 40mm and my circle to be 20mm diameter. if i add a kerf of .170 i am getting that.

As explained by LB

“LightBurn accounts for the fact that holes in a shape will need to be offset in the opposite direction, as shown here - the solid lines are the original shape, and the dashed lines are the result of shifting the kerf out or in:”

Am i not correct? Or should i be using a different method>

You are right if you reach your goal this way.
I’m just a little wary of the kerf settings if I only work with one layer because all measurements are affected

I have set a square, 50 x 50 with a circle, 25 x 25 placed inside and in the center. Put that on the blue layer set to ‘Line’. Select both and hit Duplicate, and put the duplicate on red layer, also set to ‘Line’ but has a kerf and perforation to see it easier when in ‘Preview’. All shapes are exactly the same sitting atop each other, but notice how the perforation shapes have the kerf applied. The inside shape has kerf offset in the opposite direction from the outer square shape.

You can test using the same model. Are you not observing the same? :slight_smile:

1 Like

Thanks for explanation Rick.
Let me go a step fuurther on this. If you look at my first picture, there is an additional circle on the same layer. Am i correct in saying the kerf on that circle will go outward, while using hte same layer and kerf settings?

LightBurn tries to intelligently determine if a shape is inside another and flips the Kerf accordingly. If I understand your example, the second circle is standing alone and should produce an outside kerf if set to outside. The flip happens when LightBurn finds something from the same layer “inside” another shape.

Thanks Rick, that is what i thought. My concern was when i had two diagrams in one layer.
Thanks for confirming

1 Like

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.