PLA Smoothing Tricks
Layer lines are a fact of FDM 3D printing, whether you like them or not. For those that aren't particularly fond of them, we have a few ways you can smooth out your PLA prints to get rid of those layer lines.
Sanding is one of the more accessible methods of smoothing out prints, and as you might have figured out from your own experimentation, there are many different ways of going about sanding. If you have a print with large surfaces, you might want to consider using a sanding block. They take the strain off your hands and make for an even wear on the sandpaper as well as on your print.
If you have a print with lots of detail, your best bet is to use nail files. There are many different sizes and types of nail files, and the right choice will depend on what you’re sanding, but the cheap cardboard files will often work perfectly well. You can of course also use loose sheets of sandpaper and in some situations, this might actually be preferable. To get the best results from your sanding efforts, move the sandpaper in circular motions across the print, against the grain of the layer lines.
You’ll also want to step up your sandpaper grits. Depending on the result you’re looking for, you could start as low as 400 grit sandpaper, and work your way up to 4,000 grit. On a final note, you’ve probably heard of wet sanding. High-grit wet sandpaper can be used as the final sanding stage because it doesn’t remove a lot of material and will leave a polished finish. The technique for using wet sandpaper is mostly the same as regular sandpaper, you just have to wet it every now and then.
As you probably know, PLA is not particularly heat resistant which makes it not so great for outdoor applications. But it does mean you can harness the impact of heat on the plastic to finish your prints.
The most commonly used tool for this purpose is a heat gun, set to its lowest heat setting. The best, most consistent results are attained by placing the print on a turntable and spinning it slowly to evenly distribute the heat. This also helps prevent over-melting any specific areas for an overall better result. While it might seem like a hair dryer would be a good alternative to a heat gun, a hair dryer isn’t designed to be hot enough to melt plastic, so you’ll be waiting a long time to see any change!
Another way to achieve a smooth surface on a print is by adding an additional coating of material, whether sprayed, painted, or dipped. This can fill any defects in the surface texture, including layer lines, and leave a shiny, even finish. Two common examples for PLA are using a paint primer or an epoxy coating.
Using primer on a print more or less goes hand in hand with sanding. The idea behind using a primer to finish your print is that the primer will fill in the layer lines to create a smooth surface. You then let the primer dry, and subsequently sand the top layer down. Sanding the primer is generally a lot easier than sanding down the actual PLA because the primer is a lot softer.
Using primer usually results in a print that looks a lot nicer than a print that has simply been sanded. You should, however, remember that this way is a lot more time-consuming, as you’ll have to wait for each layer of primer to dry. Additionally, it’s best to follow up a primed print with painting, as primer alone won’t stand the test of time if left uncovered.
Epoxy is a resin coating that works in much the same way that primer does. However, it’s a little more difficult to work with as you have to mix it before applying it to your print. One thing epoxy performs significantly better at than primer, though, is filling larger holes or print artifacts that have been left behind by the printing process.
Finishing your print with epoxy consists of mixing up a batch of epoxy resin. You can then apply it liberally to all surfaces of your print with a paintbrush. Just make sure that your coats are even, so you’re not left with different thicknesses on the finished print.