Ugly Prints Are Inevitable: Here is How to Learn From Them

Fortunately, the longer you spend printing, the more you pick up on the quirks and “tells” of a print. Specifically *how* a print looks bad can give you plenty of clues about the why and what you should look at to fix it.

Here are a few common reasons why your prints may look a bit “meh” instead of the clean, uniform parts you expect, and the simple fixes for them.

Wet filament

First things first: the tells for “wet” filament. If the mechanical movement of the printer is smooth but the print displays one of a range of things like the surface being covered in microscopic holes or random “zits,” is unexpectedly weak and splitting along the layers, or you can hear faint sounds of popping and hissing as the machine works, chances are the filament is moist.

Now when we say “wet” filament, it isn’t actually wet in the dunked-in-a-swimming-pool sense of the word. Filament is hygroscopic, meaning the plastic absorbs some of the ambient moisture from the atmosphere. Different filament types absorb moisture differently, and the effects are exacerbated in warmer, more humid locations.

As the filament prints, the heat from your printer’s hot end rapidly vaporizes this moisture, causing fissures in the plastic (which should be smooth and uniform). The effect can be pronounced and easy to see – a roughness that could be described as like sandpaper – or subtle, compromising the print’s strength and dulling the surface.

It’s widely reported that that filament can arrive wet from the factory, so don’t take the vacuum sealed package it comes in as sign that it’s in perfect printing condition out of the box. Fortunately, the fix is simple: dry it.

Assuming it’s PLA you are drying, place the spool on your printer’s heated bed at 45–50°C (no higher – or you run the risk of deforming the filament) for 4–6 hours. Cover the spool with a cardboard box to trap the heat. It’s rough, but works in a pinch.

Alternatively, consider investing in a filament dryer. Some can be used while you print the material, making them a handy active measure to keep your material in top shape. They’re also essential when you move on to other “high temp” materials that require hotter drying.

For a very quick (but 100% scientific) test to see if your PLA is wet, bend it. Note this is only really useful to non-filled PLAs (so not PLA-CF, for example). If it snaps like dry spaghetti, it is likely wet.

Infill Shows Through

Sometimes the outer walls of a print feel smooth to the touch, but you can faintly see the internal geometric pattern poking through the surface like a ribcage. You’re seeing the internal infill structure, used to provide prints with some rigidity, imprint on the walls.

This is often a side effect of speed. When the nozzle lays down the solid outer wall, it overlaps slightly with the internal infill to have them stick together. Because the plastic is hot and being deposited rapidly, and cools rapidly, the outer wall can subtly shrink inwards and revealing the pattern.

There are a handful of ways to address this.