To make a hole in a model you downloaded, use Bambu Studio's negative part feature: you add a cylinder to the model, mark it negative, and the slicer subtracts that volume.
The common uses are a drainage hole in a pot, a cable pass-through in a box, and vents in a lid. The same tool also works for rounding edges.
Step by step
- Place the model on the plate.
- Right-click the model → Add negative part → Cylinder.
- Move the cylinder to where the hole should be (Move tool, shortcut M).
- Set its diameter and length with Scale.
- Make sure the cylinder passes all the way through, protruding at both ends.
- Slice and confirm the hole in Preview.
If the cylinder stays inside the model, you get a cavity rather than a hole: an air pocket you cannot even see from outside.
Getting the size right
The negative part's dimensions go in as millimeters in the Size field on the right. Do not eyeball it, type the number.
Allow for clearance when you choose the diameter:
| What the hole is for | Clearance |
|---|---|
| Drainage, ventilation | None needed |
| A screw passing through | Screw diameter + 0.4 mm |
| A cable passing through | Cable diameter + 1 mm |
| A rod as a tight fit | Rod diameter + 0.1 mm |
Holes in 3D printing usually come out smaller than designed. The Bambu wiki lists material shrinkage, elephant foot, damp filament, flow dynamics and the seam as causes, so treat the clearances above as a starting point and check them with a test hole on your own printer. To correct it in the slicer instead of the model, enter half the diameter error; see the XY hole compensation guide.
Why horizontal holes come out oval
A hole through a side wall has to bridge across its top, and that bridge droops. A hole that should be round comes out flattened at the top.
The fix is a teardrop: point the top of the hole and there is no flat span left to droop. You no longer have to build one from a cylinder and a rotated cube. Under Right-click → Add negative part, Bambu Studio 2.8.2 lists two ready-made shapes. TearDrop arrives lying along Y with its point aimed diagonally up, so rotate it 45° around Y to point it straight up. Double Tear Romboid Cylinder lies along X with points top and bottom.
Hubs' FDM design guide says bridges shorter than 5 mm print without noticeable sag, and the top of a sideways hole prints much like a bridge. Holes under about 5 mm usually come out close enough; the bigger the hole, the more a teardrop helps. Keeping support out of the hole, sacrificial layer included, is covered in keeping screw holes clear.
The limits of negative parts
The model file does not change. What you did lives in the slicer project. Send someone the STL and there is no hole in it. To share the result, save as 3MF.
No dimensional checking. The program will not tell you how close the hole runs to a wall, or whether it weakens one. You check that yourself by stepping through the layers in Preview.
It does not scale. Three or four holes is manageable. Go for dozens of vents and the scene fills up with cylinders.
When to move to CAD
More than three holes, or a dimension that has to be right: CAD is faster and more accurate.
Even if you did not draw the model, you can take the downloaded STL into Fusion 360, FreeCAD or Tinkercad. Editing a mesh is coarse work, but it is enough for putting a hole in something.
The negative part method is right for one thing: a single hole, done quickly, too simple to be worth opening CAD for.
