A Complete Guide to Smoothing 3D Prints

 |  Adar Hay

Smoothing 3D Prints: Everything You Need to Know

Smoothing 3D Prints

 Image source: Pixabay

Additive manufacturing methods, such as Polyjet and fused deposition modeling (FDM) have revolutionized how we approach processes such as rapid prototyping and the creation of custom parts.

 However, if there is one criticism that is leveled against 3D printed products using techniques like Polyjet and FDM, it’s that the end result has a rough, striated, and unpleasant finish.

 The good news is that additive manufacturing has become more mainstream, and a wide range of techniques have been developed for easily smoothing 3D prints.

 So, today we’ll be teaching you how to combine all the many benefits of 3D printing with the perfect finish usually associated with traditional, but slow and expensive, manufacturing techniques.

Why Do You Need to Smooth 3D Prints?

As you might have guessed from the name, fused deposition modeling, one of the more popular methods of 3D printing, uses heat-fused deposits of materials like PLA and ABS which are extruded from the print head in stratified layers.

 These layers are normally around 0.4 mm, and provide a good mixture of accuracy and speed.

 Polyjet is another 3D printing technique that straddles the line between Stereolithography (SLA) and FDM. Polyjet printers print in layers of liquid photopolymers as small as 0.1mm and can print single objects that combine different materials and colors.

 Because both of these techniques print in layers, the prints can have a visible distinctive series of stratified layers. If you have a look at the friendly FDM printed robot below, you can clearly see those layers.

Smoothing 3D Prints

Image source: Pixabay 

Smoothing 3D prints is a vital post-processing step that helps to reduce, remove, or fill in these visible layers and create a product, prototype, or part with a clean, accurate, and professional finish.

What Are the Different Finishing Methods for ABS and PLA 3D Printed Parts?

Since PLA and ABS are two of the most commonly used additive manufacturing materials, we’ll be concentrating on what tips and techniques you can use to get an exceptional finish from products printed in these materials.

While there are some techniques that cross over between the two materials, like sanding, there are some that really don’t, like acetone vapor smoothing.

 The first step in any printing process, however, is to design your end product to specifically take advantage of the benefits of 3D printing, while mitigating its downsides.

 Programs like SelfCAD allows designers to design 3D models that ready to print as it's optimized for 3D printing. You can design models, use the in-built slicer to generate the G-Code that you will send to your 3D printer. T

who that allow them to create, render or modify 3D designs that minimize the difficult to smooth areas, stepping lines, and support adhesion points.

Smoothing ABS 3D Prints

Acrylonitrile butadiene styrene (ABS) is a common 3D printing material used because of its durability, temperature resistance, and better basic finish in comparison to PLA.

 The two most common methods for finishing ABS are sanding and filling, and acetone vapor smoothing.

Sanding and Filling ABS Prints

In order to sand your ABD print to a nice smooth finish and then fill in any voids and cover the last remnants of any stepping lines, you’ll need the following products:

●     Fine grit sandpaper; ranges between 200 and 600 grit.

●     Flexible sanding sticks in the same grit ranges.

●     Sanding sponges, handles, or blocks.

●     An acrylic brush on sandable filler. Bondo putty and XTC-3D are popular choices.

●     A sandable primer.

●     Spray paint and spray varnish (if needed).

 Once you’ve assembled the kit you need, just follow the steps below:

  1. Start sanding your ABS print using the 200 grit sandpaper. Sand in a circular motion and try not to sand in the same direction as the stepping lines or you run the risk of simply reinforcing them.
  1. Use the flexible sanding sticks to reach into any holes and hit the hand to reach places on the print.
  1. Move up through the grit levels to achieve a fine smooth surface. Remember to not push too hard or overdo the sanding. ABS takes sanding very well and you should only need to remove a very small fraction of the surface to get rid of the striations.
  1. Fill any voids or incomplete layers with your sandable epoxy, wait for it to fully dry, and then sand it down to the same finish as the rest of the print.
  1. Thoroughly wash your print to remove any sanding residue and oils.
  1. Spray your print with a sandable primer. If any rough patches show up, go back in and sand them down before recoating that area (not the whole print) with the primer.
  1. Once the primer is fully dry, you can then apply spray paints and varnishes to get the color and finish you want.
  1. When spraying your print, spray in short bursts from around 20-30 cm away to avoid gunking up your newly sanded print with thick layers of paint or varnish.

 By following these steps, you should end up with a smooth, striation-free, finish in whatever color you want.

Acetone Vapor Smoothing

Acetone vapor smoothing takes advantage of the fact that ABS melts very slightly when in contact with acetone fumes.

 While it is faster than sanding and filling, acetone vapor smoothing does involve handling hazardous chemicals, at potentially high temperatures, so it is worth approaching with caution.

To create your own acetone vapor bath, you’ll need the following materials:

    A glass or metal container that is large enough to hold your print without touching the sides, bottom, or top.

●     Strong kitchen roll

●     A timer

●     Something non-reactive to stand your print on, such as glass, metal, or aluminum foil.

●     100% pure acetone (not nail varnish remover)

●     Safety equipment such as eye protection, nitrile gloves, and a well-ventilated area to work in.

 Once you have all the materials, you just need to follow the steps below:

  1. Place your non-reactive base in the bottom of your container.
  1. Soak your strong kitchen roll in acetone and plaster it to the sides of the container so it surrounds where the print will sit.
  1. Place your print in the container, on the base, without it touching the acetone-soaked kitchen roll.
  1. Close and seal the container.
  1. Leave your print for about 15 minutes. The acetone vapor should have caused the surface to become visibly smoother and shinier.
  1. If this has happened, remove the print, being careful not to touch any of the details as the surface will be soft, and leave it to harden for at least an hour in a well-ventilated space.
  1. If the print is still matte and rough, leave it in the container, checking every five minutes, until the desired result is achieved before removing it and leaving it to harden.

 Once your print has hardened, it should be smooth, shiny, and stepping line-free. You can then color and varnish it using steps 6 to 8 from the sanding and filling guide above.

You can also create a heated acetone vapor bath, as seen in this video, which is a faster and more effective method, but it is worth noting that acetone is very flammable and the fumes are highly unpleasant, so it might be worth avoiding if you’re a beginner.


smooothing 3D models

Image by Clausabraham via Pixabay

Smoothing PLA 3D Prints

Polylactic acid (PLA) is one of the cheaper materials used in 3D printing, which makes it great for budget-friendly rapid prototyping and home printing.

 Unfortunately, PLA is a little harder to smoothen than ABS because it becomes soft and gummy when sanded aggressively and pure PLA isn’t reactive to acetone.

 To get the best finish on a PLA print, you can use a variation of the sanding and smoothing techniques we used in the ABS print.

 To do that, you’ll need:

●     Fine grit sandpaper; ranges between 200 and 600 grit.

●     Flexible sanding sticks in the same grit ranges.

●     Sanding sponges, handles, or blocks.

●     An acrylic brush on sandable filler. Bondo putty and XTC-3D are popular choices.

●     Sponge brushes

●     A sandable primer.

●     Spray paint and spray varnish (if needed).

 Once you have your kit, just run through the following steps:

  1. Using the 200 grit sandpaper, remove the worst of the obvious striation lines. As with the ABS, remember to sand in small circles and slowly, so as not to soften the PLA. This step might take some time.
  1. When the worst of the lines are gone, use the sponge brushes to apply a thin even coat of your epoxy filler. You want this coat to fill in the remaining stepping lines, but to remain thin enough so as not to gunk up your details.
  2. Once the filler is fully dry, use the finer grades of sandpaper to sand the epoxy coating to a smooth finish.
  3. You can then follow steps 5 to 8 of our above guide to sanding ABS to prime, paint, and varnish your PLA print to whatever finish you like.

 Sanding PLA prints is a little more complicated and effort-intensive than ABS prints, but with a little hard work and the right sandable epoxy filler, you can get the same smooth, line-free result.

Conclusion: Which Finishing is the Best?

As with all things related to 3D printing, the solution that works the best for you is going to depend on your specific circumstances.

 While acetone vapor smoothing is the fastest way to smooth ABS prints, you may not want to handle chemicals, or PLA printing might work better with your budget constraints.

 What is important to take away is that, using the techniques above, you can take full advantage of all the benefits of 3D printing and still get a smooth and perfectly line-free finish as the end result.


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