How to Smooth 3D-Printed Plastic Parts

By Dr. Bart Engendahl, Managing Director - Germany

Whether for form or function, many plastic parts need to be smooth. Unfortunately, additive manufacturing typically produces horizontal lines where each layer joins the next. Thus, surface finishing is often necessary before 3D-printed parts are ready for use. There are a number of ways to smooth out plastic parts produced by additive manufacturing. Or, if you want to skip straight to a smooth result, RX-AM technology with Smooth-Mode delivers a line-free finish from the start.

Sanding

The most basic way to smooth a 3D-printed part is to grind down the layer lines. This process involves using sandpaper or a file (for small details) to smooth out the rough surface. For a final shiny finish, you can apply plastic polish with a buffer. 

You can smooth the surface of any FDM material this way, although it can be extremely time-consuming — especially for detailed parts. It may compromise dimensional accuracy, as well.

Solvents

Chemical solvents can be used to eat away unwanted texture in a less hands-on way. The method will depend on the material you need to dissolve. For example, isopropyl alcohol is an option for polyvinyl butyral, or PVB.

Acetone vapor works well on acrylonitrile butadiene styrene, also known as ABS, filament. Note that acetone is not suitable for polylactic acid (PLA), which can become sticky when exposed to acetone.

For PLA, there are many other options: tetrahydrofuran (THF), ethyl acetate, dichloromethane (DCM), sodium hydroxide (a.k.a. lye or caustic soda), and methyl ethyl ketone (MEK), also known as butanone.

In general, chemical smoothing sacrifices some amount of control, which is important for parts with fine details. You risk dimensional accuracy as well as warping with large-format prints. Furthermore, many of these solvents can be hazardous to work with.

Coating

Instead of sanding down protruding lines, you can apply a coat of another material — like a primer spray, which is usually used in conjunction with sanding — to fill in the troughs.

Epoxy is another coating choice. It will impart a glossy finish, adding a protective layer and improving the strength of the underlying part. However, if you need an ultra-smooth finish, epoxy will not suffice, as it is not guaranteed to completely conceal layer lines.

Melting

Heat guns allow you to remelt the surface of your PLA part. However, excessive heat can cause warping, so this procedure requires careful attention and lots of time, too. 

Smooth-Mode

In the past, layer lines were part of the package with additive manufacturing. But new technology means that it's now possible to pre-empt these tedious finishing steps entirely. 

Chromatic's new Smooth-Mode technology yields inherently smooth, durable parts, with no need for post processing. There are no layer lines on the Z axis, and products can be printed with precise uniform thickness at a submillimeter scale. 

It's easy and affordable to print smooth polyurethane parts to begin with, so you don't have to bother with surface finishing on your 3D printing materials.

Further reading

If you would like to learn more about 3D printing smooth parts, read our press release about Smooth-Mode or contact our sales team.