I have some parts that I want to fit inside another part. I cut the outside part with no keft offset. Then I try to cut the inside pieces with the kerf size I have calculated for my machine, 0.121mm. As shown below, the parts are supposed to be 76.58 mm. I have tried kerf offsets from -2mm to +3mm and various points in between and they measure around 71.5mm. I do get a better result using the regular offset function. Why does kerf offset not seem to function? Machine is a Omtech 2024 60w with a KT332N controller. Any thoughts?
Hi Vince
Kerf Offsets are sent to the machine when the file is actually converted into Gcode (or machine code).
You can also visually check the offset on the preview; however, the dimensions of the object will not be shifted or offset when in design mode.
Most likely because the shapes are not closed:
Because LightBurn must determine the inside and outside of a shape in order to apply a Kerf Offset, this setting will only work with closed shapes.
You can use Select open shapes to find out which ones aren’t closed.
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Yes, Ed, that was one issue. The other issue is that I was interchanging inches and millimeters. I have another question. I created a square that was cut with square corners. When I add a kerf offset to the same square, it cuts with radius corners. ???
I hadda give up inches long ago … 
Because every point on that radius is exactly the kerf distance from the corner!
When you care about kerf corner shape, then you must apply the offset directly to the square (or whatever) using the Offset Shapes tool and pick Corner from the options:
The rule of thumb is that LightBurn considers a closed shape to be the “thing” you are cutting from the surrounding stock. If you want a closed shape to be the “hole”, then it must be surrounded by another closed shape that is the “thing” with the hole inside it.
It’s worth fiddling with the choices until you see how it works: LightBurn is consistent, but will produce odd results when you assume something it cannot know.
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I’m not sure I can give up inches, but I’ll try it.
What I hear you saying about the Kerf offset is not to use it in this situation. Use the offset shapes tool instead. I think I’ll look at the kerf offset video to understand how that tool is programmed to function.
Thanks for your help, Ed. I appreciate it.
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