Just wasted hours trying to adjust the kerf offset for a precision hole

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#1

Should have only taken a few minutes but here’s what is happening:

I imported a .dxf file into lightburn. In attempt to get a snug fit for my 1.5mm acrylic I adjusted the kerf on the holes outward slightly. Sometimes I would break the vectors up using the Break Apart command and sometimes I wouldn’t . Who would have thought that it matters. But it turns out that there is a substantial difference in the resulting hole sizes. You can see it for yourself by previewing the job. This goes for shapes generated in LightBurn as well. (See the rectangles in the file below)

[Duplicate Holes that aren’t] (https://1drv.ms/u/s!Ap7obl01p2cr1XsCBJ1VC2YQI3px)

If there is a reason for this then I cannot fathom it. My guess is that LightBurn doesn’t recognize inner and outer when an object is broken up and the kerf setting isn’t being applied properly. I don’t know which form is the intended right one. (broken up or whole)
When you remove the kerf offset the holes all match in size in the preview.

I can’t figure it out and even if I did I would have to have layers with different settings for both Broken apart objects and whole ones.
Any suggestions? If I just break everything apart then they would all be the same but it seem that shapes like squares that LightBurn generates are not broken apart by default. Is there a preferred state? (Connected vs Broken Apart)

This may also be related to another issue I have of lines on the table border not being cut as the kerf offset might be pushing the lines out of bounds. I am not sure yet.

Windows 7 and 10 machines act the same. LB 8.07

#2

I don’t know for sure, but I think the kerf function works only with closed shapes. The kerf setting is either positive or negative relative to the closed shape.

#3

Kerf only works for closed shapes because otherwise there is no “inside” or “outside”. The “Break Apart” function reduces a shape to line and curve segments which no longer have an inside or outside, so it’s not possible to determine the kerf direction.

And if you have shapes on the boundary that have outward kerf applied to them, this would (should) cause an out-of-bounds condition on the controller.

#4

Ah. You read it. Great. So, How might I make closed objects from open ones? I seemed to have lost that ability or never had it. If I cannot close shapes then how might I make a custom hole that has a kerf offset if needed? Must I check every object to see if it is closed? The weld function seems like it should do something like that but I am not getting closed shapes when I use it. Is there another way? All I can see doing is not using the Kerf offset and building all the adjustments into the original drawing. Bummer.

BTW If I select the open green shape in my file there is no option to Close Path (Greyed). If I, Select Open Shapes, then the Close Path option is no longer greyed out but does nothing when selected. Edit: But, Auto Join Selected Shapes DOES close them. Little confusing but I’ll get it.

Thanks again

#5

I see what you mean about the close path command - seems like it should do the same thing as the Auto join selected shapes command from how I read it: https://github.com/LightBurnSoftware/Documentation/blob/master/MenuCommands.md#EditMenu Could this be a bug or does the Close Path only work if the endpoint are NOT touching? I couldn’t get the Close Path command to do anything.

#6

“Join” connects two disconnected shapes.
“Close” closes a single open shape, but doesn’t try to connect it to anything else.

Both have a pretty tight tolerance, and I want to make them pop up a threshold and make it more interactive, kind of like the ‘Optimize Shapes’ dialog.

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#7

You said “‘Close’ closes a single open shape, but doesn’t try to connect it to anything else.” Now it makes sense! The case JoshephShawa provided is 4 (or more) individual lines who’s points are identical but are in reality four open shapes. I can see how closing a single line would be difficult to figure out or, at best, would result in a pretty funky closed shape or possibly a circular object. Thanks for the explanation.

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#8