For a test I duplicated a slot from 2 to 1. When I cut slot 1 with a -.08 kerf offset it worked great.
Then I cut the whole design (2) and the slot was too big. As if it didn’t apply the kerf offset.
Both one and two are on the same layer with the same settings.
This happened twice. Can’t figure this one out.
Shape 1 is outside any enclosing shape, so a negative kerf offset makes it smaller.
Shape 2 is inside the enclosing shape, so a negative kerf offset makes it bigger.
The doc shows the effect:
Note the difference between the outer circle and the inner circle in both cases.
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Argh. That’s not confusing at all…
So both shapes show -0.8 as inward in the kerf offset setting.
I even separated the two on different layers and they showed the same.
That makes it even more confusing and counterintuitive.
Only until you understand what’s going on.
LightBurn applies the kerf to the entire “object” it finds in your layout.
The object you labeled 1 is a rectangular block. Applying an inward kerf to that rectangle makes it smaller.
The object you labeled 2 is the large enclosing rectangle with two smaller holes removed from it. Applying an inward kerf to the large enclosing rectangle makes it smaller, thus making the interior holes larger.
The rule goes something like this:
- Draw a line from far away toward the point you’re interested in
- If the line crosses an odd number of borders, the point is inside a shape
- If the line crosses an even number of borders, the point is outside a shape
So the isolated little rectangle labeled 1 is a shape all by itself: an inward kerf makes it smaller.
The little rectangles inside the big outer rectangle labeled 2 are outside the larger rectangle: an inward kerf applied to the larger rectangle makes it smaller and, thus the little rectangles become larger.
I appreciate your explanation. I don’t mean any offense but as an average end user that seems way more complicated than it has to be.
I simply want the slot to be smaller. Why would I want the #2 larger rectangle to be changed at all?
If you don’t want the larger rectangle changed, you could put it on a different layer with no kerf adjustment. Then your slots would cut correctly on the layer with the kerf adjustment.
This is probably a situation where it’s better to use the resize slots function. Kerf offset pplies to the entire layer, resize would only affect your slots, which is what you’re working with.
Here’s another way to think of it.
LightBurn assumes you are cutting a thing out of a big sheet of material:
- That thing is what you care about
- The sheet goes back on the shelf for next time
In your first case, you’re cutting a little brick out of the material. Because you applied a negative kerf, the brick gets smaller.
In your second case, you’re cutting a big rounded rectangle out of the sheet, but that rectangle has two little holes in it. Because you’ve applied a negative kerf, the big rounded rectangle gets smaller, which means the two holes must get larger.
