Exactly where does PrusaSlicer place filament traces (hole clearance question)
Here is the simple case. Square box with a hole through it. Box is 10x10 with hole diameter 6. If I measure the printed part the box is, in fact, 10.05x10.05 (actually very slightly larger but much less than the nominal width of the outer perimeter setting which is .45). So from this it would seem that the slicer is placing the perimeter trace such that the edge of that trace is in the correct spot. That is, allowing for half the width of that trace it would need to be placing that trace center .225 in from the ultimate edge.
On the other hand, the behavior for the hole seems different. If I measure that hole it prints at ~5.6mm which is what I would expect if the center of the edge perimeter of the hole were placed on a circle 6mm in diameter. That is, here the slicer seems to be putting the trace on the nominal edge of the model. For creating precise holes this needs to then be compensated for.
I can understand either approach in the slice (although I think the slicer should actually allow for the width (of actually half-width) of the actual trace when locating the travel line. What I don't understand is the difference in behavior between outer external perimeters and internal outer perimeters.
Does anyone understand what is actually going on so that I can reliably design to it?
Thanks.
RE: Exactly where does PrusaSlicer place filament traces (hole clearance question)
I've found that when designing clearances for 3d printing, the only way to reliably get them correct is to do a test of the case and adjust as needed.
For such things as small registration pegs, I've found that .1mm difference between the peg and the hole is usually about right, but it depends on many factors, like your nozzle diameter, filament type, layer height, and what plane(s) your pegs/holes are printed on.
RE: Exactly where does PrusaSlicer place filament traces (hole clearance question)
I pretty much always do tests for this as well. It was actually doing a test for a metal self threading screw that I noticed that my initial guess for the hole seemed a lot off so I actually measured the result which is what led to the question. I was surprised that my initial design hole size printed so far smaller. That left me trying to understand why that would be.
RE: Exactly where does PrusaSlicer place filament traces (hole clearance question)
For a recent project, for the projections into which I screwed regular M2.5 screws, I did the holes at 1.2mm radius. That worked well for a force-self-tap and held quite well.
I forget whether I printed that one in PLA or ABS.