I’m coming more and more to the conclusion that Affinity Designer isn’t as great for preparing cut files as Inkscape. Inkscape is basically a really fancy SVG editor, which is very handy for Glowforging. AD SVG export is more of a way to convert what you have on screen into SVG, which is not the same thing at all.
Case in point: I wanted to put a cut line around some objects, so I drew a no-fill rectangle around them and went to cut it. To my surprise, I had to convert engrave to cut, then the Glowforge took what looked like a double cut on the rectangle path. On closer inspection, it really took two separate cuts, leaving a tiny sliver outline.
What’s going on is that when AD converts a rectangle into SVG, it is actually converting it into two paths that represent the rectangle’s stroked shape as it appears in Designer, including all the miters or rounded corners and what not. When Inkscape does the same thing, it just spits out a single rectangle path and uses SVG style properties to record the stroke width, join styles, etc.
I’ve been looking for a way to get that behavior out of Designer. Convert to Curves does nothing useful in that regard, it ends up outputting the same stuff. Expand Stroke (called Stroke to Path in Inkscape) makes the double path thing explicit, so at least you can delete one of them, but that messes up your geometry. The easiest thing to do is to use a fill/no stroke rectangle (and move the layers around so that it’s in the background and not overlaying everything), which exports properly. Then you have to convert the engrave to a cut in the GFUI.
Just FYI, for fellow Designer users. I hate having to fire up X11 on a Mac, but once you get used to it, Inkscape turns out not to be half bad.