Somewhere on here I stumbled upon a post about acrylic kerf settings. There was a link to a short video where the user was showing a black and white piece they had made, where the black cutout would basically just fall out of where they were putting it into bigger piece. They cut the same shape in white, with slightly different size settings, and the white piece stays perfectly. I’m going to try a small acrylic piece using two different colors, and was hoping to find that article before I try. I definitely want the inlay to be a perfect fit…
Just look for kerf adjustment in general. Acrylic, wood, etc, doesn’t matter what material you use, the techniques are the same.
I use the stroke width, stroke to path, union/different method, myself, but you can do it with offsets. The only variable is how much you’re offsetting, and that depends a lot on your material and settings, so nobody can give you a magic bullet there. For wood, I start at 0.005 for looser fits, and go up to .009 for “omg I need a hammer to put it together, what was I thinking never again”. Acrylic has less give than wood, so ymmv.
I’ve done this a few times to make curb house numbers. I cut “holes” for the numbers out of white acrylic. Then I cut the numbers out of black acrylic—but as a mirror image. This is because the cross section of the laser cut is more of trapezoid (i.e., wider at the bottom than the top) than a rectangle.
If you want a tight fit you need to “grow” the letters by the needed “kerf” amount. That’s a bit complex in Inkscape. The subject has been covered here before. I use something like 0.1 mm as the kerf adjustment, but your mileage may vary, so a test would be required for your particular Glowforge and material.
It is all a bit different with different thicknesses of material. And the variation in the tolerances of acrylic adds another variable. If I am going for friction fit in acrylic or an inlay, I makes sure I do a test piece on the particular sheets of acrylic I am using and make sure I measure around the perimeter of the sheet.