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Why holes print undersized

The screw does not drop in, and the model was not wrong. Plastic shrinks when it cools, and that shrinkage hits the hole harder than the outside. Do not scale the whole STL. Loosen the hole in the design, or open it in the slicer with XY hole compensation.

Tips & TricksSlicer Settings 0:57

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How to make a screw hole fit after it shrinks

  1. 1 The model was not wrong

    You designed a hole for a screw. The screw does not drop in, so you drill it out and blame the file. Plastic shrinks when it cools. Bambu says that contraction makes holes smaller.

  2. 2 Do not scale the whole STL

    Bambu’s shrinkage setting mostly scales the outside, not the hole the way you need. Growing the whole part to open one hole also grows every other feature. Leave the outer size alone.

  3. 3 Model the hole a bit loose

    Clearance belongs in the design. Model the hole a bit loose on purpose, with extra gap so the screw still fits after the plastic shrinks. That is the first fix, before you touch the slicer.

  4. 4 Add XY hole compensation

    In Bambu Studio or Orca, open Quality, then XY hole compensation. Try +0.1 to +0.3 mm. That opens the hole without growing the whole part.

  5. 5 First-layer squish can still pinch it

    Even with compensation, first-layer squish can pinch a hole tighter. Prusa calls that elephant’s foot. It shows up especially on ABS, which shrinks more after cooling.

FAQ

Why is a designed hole smaller on the print?

Filament contracts as it cools. Bambu says that contraction makes holes smaller. The CAD hole was the size you drew. The cooled plastic is not.

Should I scale the STL until the screw fits?

No. Scaling grows the outside too. Bambu’s shrinkage setting mostly scales the outer size and does not open internal holes the way you need. Use clearance or XY hole compensation instead.

Where is XY hole compensation?

In Bambu Studio or Orca, open Quality, then XY hole compensation. Try +0.1 to +0.3 mm. A positive value opens the hole without growing the rest of the part.

Why is the hole still tight on the first layer?

First-layer squish can pinch it. Prusa’s elephant-foot compensation is for that bulge. It is worse on ABS, which also shrinks more after it cools.

Full transcript

You designed a hole for a screw. The screw does not drop in. You drill it out and swear the model was wrong. It was not. Plastic shrinks when it cools. Bambu says contraction makes holes smaller, and their shrinkage setting mostly scales the outside, not the hole the way you need. So don't scale the whole STL. Two real fixes. Clearance in the design: model the hole a bit loose on purpose, extra gap so the screw fits after shrink. XY hole compensation in the slicer: in Bambu or Orca, open Quality, then XY hole compensation, and try +0.1 to +0.3 mm. That opens the hole without growing the whole part. First-layer squish can still pinch it tighter, especially on ABS. Or skip the headache. Obloid's Parametric generator builds print-ready parts with clearances you can prompt.

Sources

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