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Under-extrusion around the edges of circular holes

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I seem to have a problem where whenever I print a part with a vertically aligned small (2mm to 4mm range of diameters) circular hole through it the printed perimeters of the circle seem to barely touch the main infill (and at the upper facing surfaces barely touch the top covering layers). I found a guide online "Gaps Between Infill and Outline" ( and and have tried slowing print speed and increasing extrusion multiplying but still get these. It particularly affects holes for screws to go in to or for thin axles to rotate in. I've also tried all manner of different infills, even fully solid, and tried Cura's setting for having extra perimeters on alternate layers, neither helps. Hole ofset settings don't afect this, they make the bore of the hole wider but then the area where the under-extrusion between the hole's perimeter and the infill happens simply gets shifted to a slightly wider diameter accordingly. I have increased perimter-infill overlap settings to the point it starts to affect the geometry of the outer wall, but while the outer wall is connected to the infill just fine for any setting, the inner walls around holes still keep this under-extruded "gap" area between them and the infill. I adjusted the overlap settings right up to the point where Cura thinks it is too large and turns the box orange, and then larger still, an still get the "gaps". Trying to change printing order to do infill before walls didn't help either.

I have "connect infill lines" and "fill gaps between walls" both turned on.

I'm using Cura as my slicer and the printer is a CR20-Pro.

I'll post some photos later, but the one in that guide is reasonably representative of my situation, a little more severe perhaps in that theirs are full gaps wheras mine is more like serious under-extrusion. And it only happens with circular (or close to circular) holes, and fairly small holes at that, No such issues have occured for holes sized at a cm diameter or more.


Yes photos please :)

It sounds like your small circular shapes are shrinking after being deposited.  This is normal but sometimes too much occurs and it's annoying.  Try measuring the internal radius of the hole with calipers and see how much it has shrunk vs the original model.

In my experience: some filaments are just garbage and shrink a lot.  Others can be improved by drying them.  Some are mostly perfect all of the time.

Can't post photos yet (give me a few hours before I'm in the right place), but in so far as I can measure the internal diameters of small holes (tricky to get caliper tips in to small ones) Thy are printed with 0.3mm clearances for 3mm bars to fit in to, and yet always need some "filing" out with a drill bit for a bar to be fitted in. The holes are always a bit undersized. Surely there is a way to fix this in settings though rather than have to get different filament.

Undersized holes can be mitigated by:
 - making them bigger in the original model (very effective, but of course annoying)
 - setting XY expansion to a negative number like -0.1mm in Prusaslicer (not sure if this has an equiv in Cura, plus it distorts other parts of the model too)
 - telling your slicer to lay infill BEFORE walls sometimes helps
 - filament drying or replacement (as per my prev post)

The first two options will of course not fix your problem with walls not touching infill for small radius holes.

If you are 0.3mm oversizing your hole but still having them undersize then you are seeing a lot of shrinkage.  What plastic are you using, if I may ask?

Fun fact: different colours of the same brand have drastically different properties.

Photos, here are some of the very worst examples, all of holes in the 2.5mm to 3.5mm range:

Undersizing of the holes themselves isn't really a problem, I've got in to the habits of leaving tolerances for this. The issue is ofcourse the walls being poorly connected to the infill. And infill before walls doesn't sem to have helped. If I could force the slicer to do something like 4 extra walls lines, not just 1 extra, on alternate layers I might have a hope.

I am using "eryone" branded PLA (grey), it has tended to work quite well and is what I've been running on ever since shortly after I got the printer, i went through a while of testing filaments from several brands and this one behaved best. When I say 0.3mm oversizing I mean 0.3 oversizing the diameter, so only 0.15 oversizing the radius, the shrinkage, or perhaps other effects means the actual hole comes out at just under 3mm, not substantially under, almost loose enough to force a 3mm metal rod in but not quite. And this undersizing mostly seems to only apply for small holes, large holes through parts seem to maintain expected dimensions better.

I found the under-extrusion in the areas between inner perimeter and infill particularly problematic recently, I had been tolerating it but I've had a case where a part broke in use when a screw (with nut) was tightened in to a hole because the hole wall and infill weren't well connected. I hoped I might finally find a fix now.


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