PLA Smoothing: How to Smooth 3D Prints

When it comes to 3D printed texture, some people love it, and some people hate it. Nevertheless, there are many reasons that you may want to finish a print and give it a smoother surface. Maybe it’s a display piece, or perhaps you need to reduce friction between moving parts.

As the most common 3D printer filament, it’s worth knowing how to post-process PLA. Sadly, the nature of the material means acetone smoothing isn’t an option, but there are other ways to achieve a smooth and shiny finish.

In this article, we’ll take you through different ways of smoothing out and finishing your PLA prints. We’ll start with the basics, like trimming and sanding, before moving on to different ways to coat or even melt the surface of a part for a smooth finish.

If all of that sounds like more effort than you can put in at the moment, try Craftcloud. With a wide range of available finishes, you can get parts professionally printed in PLA and finished to your specifications.

Before Printing: Slicer Settings

While smoothing takes place after the part’s printed, makers can take advantage of several features and tools in the slicer beforehand to try to minimize the post-processing.

• Z seam: Every layer has to start and stop extruding at some point, which creates a small “zit” or “seam”. Slicers like UltiMaker Cura or PrusaSlicer have settings that allow makers to place this “Z seam” on the inside of sharp corners, for example, which reduces surface roughness.

• Ironing: Many FDM slicers also have options to “iron” the top layers of 3D prints, where the hot extruder retraces the top layer to smooth the material.

• Vase mode: For certain geometries (notably vases), slicers can enable “vase mode“, which 3D prints the object with one singular wall in a clean spiral. This facilitates a clean transition between layers, eliminating the Z seam because there are no stops and starts in layer shifts.

• Orientation: Fewer supports mean fewer problems when removing them, and gradual overhangs mean decreased chances of poor bridging. Changing the orientation of the part so that it has no supports or overhangs over 15 degrees can ensure a 3D print that comes off smooth. If your 3D printer is a dual-extruder, dissolving supports can help decrease or eliminate these problems altogether.

In addition to these slicer features, it’s important to have dialed-in retraction settings for the specific material in use. This is because inadequate retraction settings can lead to stringing, which takes a lot of effort to remove. Stringing can also be reduced by drying the filament before 3D printing, which is especially important for hygroscopic materials like PETG or TPU. Lastly, smaller layer heights will lead to better defined 3D prints – at the expense of a longer 3D printing time.

Having gone over the “before”, let’s go over the “after” ways of smoothing PLA 3D prints.

Removing Excess Material

To remove supports, brims, rafts, or stringing artefacts, flush cutters are the best tool to use. Used with caution, they can effectively remove filament from flat surfaces, leaving very little – if any – material.

For places where the flush cutters can’t effectively remove material (for example, because they can’t fit into tight corners), a utility knife can be used. It’s important to follow safety measures to minimize the chances of injury:

• Never use a utility knife with someone else within two meters of your work area.

• Always point and move the knife away from you (including away from your other hand, which might be holding onto the 3D print). If this isn’t possible, use a vice clamp to secure the part to a table before continuing.

• Make sure that the knife blade is sharp and has no visible defects.

• Don’t force the knife to the extent that it might slip or break; if you find yourself forcefully shaking while trying to use a utility knife, the cut should be made using a different method.

Sanding

Sanding is one of the more accessible methods of smoothing out prints. As you might have figured out from your own experimentation, there are many different ways of sanding 3D prints.

If you have a print with large surface areas, consider using a sanding block. They take the strain off your hands and create even wear on the sandpaper and 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.

Of course, you can also use loose sheets of sandpaper, which may be preferable in some situations. 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.

Surface Melting

As you probably know, PLA is not particularly heat resistant, which makes it unsuitable for outdoor applications. However, you can still 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.

And while it might seem like a hairdryer would be a good alternative to a heat gun, a hair dryer isn’t designed to be hot enough to melt plastic. Many models won’t be able to reach temperatures that are suitable for a gentle surface melt.