Design better holes: fillet, orient & size for shrink
A hole seems like the simplest feature there is, and it’s one of the easiest to get wrong. Small fillets, the right orientation, and a shrink allowance turn a rippled, undersized hole into a clean one.
Applies to
- Process
- FDM / filament
- Features
- Through-holes, bores, pilot holes for screws
- Orientation
- Holes printed on their side vs. flat
Why it matters
A hole punched straight through with perfect sharp corners can ripple, because the nozzle can’t trace an infinitely sharp corner — small fillets give the tool path a smoother motion and a cleaner edge.
Holes printed on their side sag at the top and print undersized as the plastic shrinks, so a nominal hole ends up too small for the pin or screw it was meant to take.
What good looks like
- Hole edges carry a small fillet or chamfer, not a raw sharp corner
- Sideways holes use a teardrop or are oriented to avoid a sagging top
- The modeled diameter includes a shrink allowance so the real part fits
How to apply it
- Fillet or chamfer the mouth of the hole so the tool path flows.
- Where you can, orient the hole so it prints flat (axis vertical) for the roundest result.
- For a horizontal hole, teardrop the top or accept it’ll need reaming.
- Add ~0.1–0.25 mm to the diameter as a shrink allowance and test-fit the mating part.
Common mistakes
- Modeling the hole at the exact nominal diameterOversize for shrink, then fine-tune from a test fit
- Printing a large hole horizontally with a flat topTeardrop it or reorient so it doesn’t sag
Filleting hole edges, teardrop orientation, and sizing for shrinkage — Design Better Holes | Improve Tolerances | Reduce Sagging ↗.
Summarized and independently edited by Start Here. Starting values and cautions are our editorial notes, not a quotation from the creator.