Holes printing undersized?

Out of curiosity (before I re-print a whole set of parts for SS tubing) what would cause holes to print undersized (IE I have to thread the bolts into them, slight interference fit, instead of them being slip fit) while the exterior dimensions of the model are fine? I printed a 100mm test piece and it measures exactly 100mm.

I usually just design in an offset for 3d printed holes and I’m assuming Ryan did the same… but I’d rather the parts print properly than have to run a drill through the holes again. Since I don’t know what else the error is affecting other than the undersized holes.

My thought was maybe I’m slightly over-extruding and have the steps/mm slightly too low, which would make the exterior dimensions come out correct but shift the holes to be too small.

You can try a few things, but I’m curious which holes are giving you trouble? Ones that print parallel to the bed, or ones that print vertically?


If all your belts are tight and linear motion is solid, you can try a horizontal x/y compensation of -0.1mm, or maybe slowing down a lot on the holes themselves, usually considered small/short perimeters.

The holes are not necessarily a slip fit. 8mm or 5/16?

Filament shrinks so all inner diameters should be slightly small…because of that I have slightly oversized them. They should be tight though, a slip fit would be bad.



The problem on my original build was that the bolts were “threading” in to the plastic so that even with the nut not on, the bearings were clamping the rails too tightly. So I disassembled the whole machine and ran a 5/16" drill bit through every hole.


Aaron: both, which I realize are separate issues now that you mention it. lol. I try to avoid printing holes standing up so I wasn’t as worried about that.