What is a teardrop hole in 3D printing?

A round hole with a point added at the top, so the roof of the hole is two 45° slopes instead of a flat bridge. It prints without sagging and still holds the fastener on its round sides.

Why do horizontal holes come out oval in 3D prints?

The top of a horizontal hole is a short bridge, and bridges sag. That droop flattens the top and makes the hole oval and undersized.

Does a teardrop hole make the fit looser?

No. The round part of the hole still touches and constrains the screw or dowel. The point is just empty space above it.

Which way should a teardrop hole point?

Straight up, in the direction the part prints. If you rotate the part on the bed, rotate the teardrop with it.

3D Printing3D Modeling / DFMTeardrop side holes

How do you stop horizontal holes sagging in a 3D print?

You print a hole through the side of a part and the top droops. Not much. Just enough that the screw drags instead of dropping through. Teardrop holes in 3D printing fix that: a small point added to the top of the circle, so the printer never has to bridge across a flat roof.

⚡ Rule of thumb

Fillet the edges of a side hole, then add a point to its top to make a teardrop, so no layer has to bridge across the roof of the hole.

Starting point

Point formed by two lines tangent to the circle, each 45° from vertical

Measured

Flank angle from vertical, in print orientation

Confidence

Widely accepted

▶ Source video — Design Better Holes — Slant 3Dwatch on YouTube ↗

Applies to

Process: FDM / filament
Features: Through-holes in a side wall, axis lying flat on the bed
Fasteners: Screws, dowels and pins meant to slide straight through

Why it matters

When a side hole prints, the layers climb up both walls of the circle, closer and closer together. Then the last stretch at the top is basically a flat line straight across. The printer has to bridge it.

Bridges sag. So the roof of the hole droops, and the hole goes oval.

Slant 3D’s point is what that costs you. A screw that should drop through a loose clearance hole now drags, and you end up driving it all the way in by hand.

The edge matters too. A raw, sharp hole edge ripples, because the nozzle and the machine’s motion can’t trace a perfect corner. A small fillet smooths the path out.

What good looks like

Small fillets where the hole breaks through each face
A point on top, so the hole reads as a teardrop
The round part of the hole still matches the fastener and locates it
No droop or loose strands across the top of the hole

How to apply it

Model the hole at its normal diameter plus your shrink allowance.
Fillet the edges where the hole breaks through each face.
From the top of the circle, draw two lines tangent to it, each 45° from vertical, meeting in a point.
Trim the arc above the tangent points so the outline is a teardrop with its point straight up.
Check the point faces up in the print orientation. Rotate the part on the bed, rotate the teardrop with it.
Extrude the profile through the wall.

Test it on your setup

Print a plate with one plain round side hole and one teardrop hole of the same diameter.
Slide the real screw or dowel through each one.
Look at the top of each hole. The round one shows the droop; the teardrop’s roof should be clean.

Exceptions & tradeoffs

Electrical enclosures and industrial brackets can usually live with a little sag. Slant 3D calls it not the end of the world. Add the point when the fit matters: a loose screw, a dowel, a shaft.

Small holes only bridge a short span, so they sag the least. Big side holes sag the most and get the most out of a teardrop.

If a point looks wrong on a cosmetic face, a flat-topped teardrop works too. Cut the point off with a short flat bridge. It’s a short enough span to print clean.

Common mistakes

Punching a plain round hole through the side and hopingAdd a point to the top so it prints as a teardrop
Rotating the part on the bed and leaving the teardrop pointing sidewaysThe point always faces up in print orientation
Making the whole hole bigger to fight the sagKeep the round profile true; the point handles the sag
Leaving the hole edges razor sharpAdd a small fillet so the tool path flows

Frequently asked questions

What is a teardrop hole in 3D printing?A round hole with a point added at the top, so the roof of the hole is two 45° slopes instead of a flat bridge. It prints without sagging and still holds the fastener on its round sides.
Why do horizontal holes come out oval in 3D prints?The top of a horizontal hole is a short bridge, and bridges sag. That droop flattens the top and makes the hole oval and undersized.
Does a teardrop hole make the fit looser?No. The round part of the hole still touches and constrains the screw or dowel. The point is just empty space above it.
Which way should a teardrop hole point?Straight up, in the direction the part prints. If you rotate the part on the bed, rotate the teardrop with it.

Slant 3DSource & visual reference

A plain hole punched through the side ripples; small fillets give a cleaner hole — Design Better Holes | Improve Tolerances | Reduce Sagging ↗ at 00:13.