Holes and Parts Printing the Wrong Size? Fix Dimensions With XY Compensation

You designed a 5mm pin to slot into a 5mm hole, printed both, and now the pin will not go in. The hole measures closer to 4.7mm and the outer wall of the part is a fraction wide. This is the classic FDM dimensional bias, and the cure is XY compensation (called Horizontal Expansion or X-Y Hole Compensation depending on your slicer). It nudges the toolpath outward or inward to land your printed sizes back on the numbers you actually drew.

Quick Answer

Printed holes come out undersized and outer dimensions come out slightly fat because the nozzle drags molten plastic inward and the material shrinks as it cools. Set a positive XY hole compensation of about 0.10mm to 0.20mm (radius) to open holes back up, and use a small negative horizontal expansion if your outer walls measure oversized. Print a calibration cube first, measure with calipers, then dial the value.

Why Holes Shrink and Walls Grow

Two forces bias every print inward at the hole and outward at the perimeter. First, thermal shrinkage: PLA pulls in roughly 0.2 to 0.4 percent as it cools, ABS and PETG more. Second, nozzle drag, the molten bead is pulled toward the hot nozzle as it travels the inside of a circle, so curved internal walls close up more than flat external ones.

The result is predictable. A hole prints a few tenths of a millimetre too small, while the outside of the part prints a touch too large because the extruded line has real width and tends to bulge. That is why a peg and a socket designed to the same nominal size end up with an interference fit you never asked for.

The Fix: XY Compensation In Your Slicer

In Cura the setting is Hole Horizontal Expansion (and Horizontal Expansion for the whole outline). In OrcaSlicer and Bambu Studio it lives under Quality, Precision, X-Y Hole Compensation and X-Y Contour Compensation. In PrusaSlicer it is XY Size Compensation in the Advanced tab.

Remember the value is applied as a radius, not a diameter. If your 5mm hole prints at 4.7mm, you are short 0.3mm on diameter, so you add roughly 0.15mm of positive hole compensation. Apply a separate, usually negative, contour value if the outside of the part measures large. Treat the two independently because they correct different errors.

Calibrate, Do Not Guess

Print a 20mm calibration cube with a 10mm hole through it, then measure all three axes and the hole with digital calipers. Work out the difference, halve it for the radius, and enter that as your compensation. Reprint and confirm. One round of measurement beats a dozen reprints by feel, and the value you land on tends to hold steady for that filament and nozzle. A solid set of digital calipers from the 3D printing tools and accessories on the Evetech best sellers shelf makes this a five minute job rather than a guessing game.

Frequently Asked Questions

Does XY compensation fix vertical holes too?

It corrects holes printed in the horizontal (XY) plane, which are the round bores most parts rely on. Holes that run sideways through a part (along the Z face) often print as slight ovals from sagging, and compensation does not fully cure those. Add support or a teardrop hole shape for sideways bores.

How much should I add for PETG versus PLA?

PETG and ABS shrink more and ooze more, so they usually need a slightly larger positive hole value than PLA. Start at 0.15mm for PLA and 0.20mm to 0.25mm for PETG, then measure and refine. The exact number depends on your nozzle and flow calibration.

Will this throw off my outer dimensions?

Only if you apply it carelessly. Keep hole compensation and contour compensation as separate values. Opening a hole does not have to change the outside of the part, and most slicers expose the two settings precisely so you can correct each error on its own.

Should I just oversize the hole in CAD instead?

You can, and for a one-off that is quick. But a slicer compensation value fixes every hole in every future print on that machine automatically, so you draw to true size and let the printer correct itself. That is the cleaner long term habit.