How to fix stringing in 3D prints: retraction, heat and dry filament

Your print looks great, except it's covered in fine hairs, as if a spider moved in overnight. That's stringing. Today: why it happens, and three fixes that clear it up.

Thin threads across every gap. Little blobs on the walls. And a cleanup job with a knife after every print.

Pause and guess. When does a string form? A: while a wall is printed. B: while the nozzle jumps across a gap. Or C: while the part cools?

It's B. Strings are born in mid-air, during the jump.

Inside the hot nozzle, the plastic is molten and under pressure. When the nozzle stops printing and jumps to the next part, a little keeps leaking out. The nozzle drags it along, and it cools into a thread.

How much plastic is that? A hair-thin string across a 20 millimeter gap holds the plastic of about 0.07 millimeters of filament. Less than a tenth of a millimeter. So even a tiny leak is enough.

So here's this episode's free model: four pins on a strip, with gaps of 5, 10 and 20 millimeters. Every layer, the nozzle has to cross every gap. 25 millimeters tall, at 0.2 millimeter layers? That's at least 125 jumps per gap.

With bad settings, it looks like this. The long gap usually strings first, because the nozzle spends longer in the air.

Fix one: retraction. Right before the jump, the extruder pulls the filament back a little. The pressure drops, so nothing leaks while the nozzle travels.

Your profile already has a retraction length. Direct drive printers usually stay under about two millimeters, Bowden setups often need several. Raise it in small steps. Too much can pull soft plastic into the cold part of the hotend, and cause a jam.

Fix two: temperature. Hotter plastic is runnier, so it leaks more. Lower the nozzle temperature 5 degrees at a time, and stay inside the range on the spool. Too cold, and the layers stop bonding well.

Fix three: dry your filament. Many filaments soak up moisture from the air. In the nozzle, that water turns to steam and pushes plastic out, retraction or not. Popping or crackling while it prints is the giveaway.

PETG is famous for it, as we saw in Material Match number one. Dry it the way the filament maker says, and store it sealed, with a bag of desiccant.

Change one thing at a time, and print the test again. Clean gaps? Done.

In short: tune retraction in small steps, lower the temperature 5 degrees at a time, and keep your filament dry.

The stringing test is free to download. Tell me in the comments: which fix cleared up your strings? Next time in Fail of the Week: warping, when the corners of your print lift off the bed. Subscribe so you catch it. I'm Spoolbert, see you in the next one.