Droopy sideways holes? Teardrop holes fix them (no supports)

You design a nice round hole, lying sideways through your part. It comes off the printer with a saggy, stringy ceiling. Can you print a sideways hole cleanly, without supports?

Without support, the top of the hole droops. With support, you're digging plastic out of a tiny tunnel. And either way, your bolt may not fit anymore.

So here's this episode's test block. Three 8 millimeter holes: a plain round one, a teardrop, and a teardrop with its top cut flat.

Remember the 45 degree rule from the first episode of this series? Each new layer may stick out a little past the one below, but not more than about 45 degrees.

The bottom half of a round hole is easy. But near the top, the circle flattens out. The last layers reach too far in, and the very last one has to span the gap on thin air.

Colour the block by overhang and you see it. In the round hole, the whole top quarter of the circle is red. In the teardrop, there's no red at all.

Here's the trick. Keep the bottom of the circle, and replace the top with two straight lines at 45 degrees, meeting in a point. Now every layer rests on the one below.

The point makes the hole a bit taller. For an 8 millimeter hole, the tip sits 1.66 millimeters above the circle. That's just air. Your bolt sits in the round bottom and never notices.

Pause and guess. Which way should the point face? A: up, away from the bed. B: down, toward the bed. Or C: it doesn't matter?

It's A. Up, the direction the layers grow. The point is the roof.

And up means up on the print bed, not in your CAD drawing. Lay the part on its side, or flip it, and the round part of the teardrop ends up on top. That droops just like a plain round hole.

Don't want the pointy bit? Cut it off level with the top of the circle. The hole is exactly as tall as a round one, with a flat bridge of only 3.3 millimeters.

On the test block, that bridge is the only red left. But a short, straight bridge, held at both ends, is something printers handle well. A droopy curved ceiling isn't.

When do you need this? Only for holes that lie sideways. Upright holes print fine as circles. And small holes often get away with it: in a 3 millimeter hole, the droopy part is only about 2 millimeters long. The bigger the hole, the bigger the droop.

Does the rest of your part still need support? Then look for an option like 'on build plate only'. Support can then only start on the bed, so it can't grow inside your holes. Names differ per slicer.

In short: use teardrops for sideways holes, point them up as the part sits on the bed, and use a flat top when the height matters.

The test block is free to download. Print it and compare the three ceilings. Then tell me in the comments: round, teardrop or flat-top, which one printed cleanest for you? I'm Spoolbert, see you in the next one.