Post-Processing

While there are numerous methods of finishing your 3D printed parts, we will focus on some of the most common methods:

• Sanding
• Vapor Smoothing
• Painting

Of course, there are more complex methods for post-processing your 3D printed parts, such as epoxy coating or metal plating. While many of these could be completed in your workshop, it is often a great option to send the work out to a specialty shop to ensure your get clean, professional results the first time. Many methods require a degree of skill and experience. The devil is always in the details!

Other methods that won’t be covered today, but perhaps in a later blog post, include electroplating, machining, support material removal, sandblasting, coating, tumbling, dyeing, annealing, and many more!

Sanding 3D Printed Parts

Sanding may be the most commonly used method to post-process 3D printed parts. It is safe and inexpensive but does require a bit of elbow grease if you don’t have an orbital sander or a belt sander. Investing in powered sanding equipment can potentially save you hours of time sanding by hand.

To get great results, following these steps and be careful not to skip any. It is easy to get too excited and rush the job. This will always make your results worse. Patience is key!

1. 3D print your part in a “sandable” material. While just about any 3D printable material from PLA to metal is sandable, some are much more difficult than others. Selecting the correct material for your application is key to minimizing your cost and getting great results. In the world of FFF, PLA and ABS are very common materials and have the benefit of being easy to sand. Sanding FFF parts made of materials such as carbon fiber reinforced materials is possible, but requires much more time, effort, and sandpaper!
2. Start Coarse. Start with a coarse grit sandpaper. If you have a layer height less than 250 microns, then you should start with 150 grit. If you have a layer height greater than 250 microns, then you should start with 100 grit. Using these coarse grit sandpaper grades will enable you to more quickly smooth out the contours formed by each bead of material.
3. A little less coarse. Move on to a finer grit of sandpaper. Once you have done the first pass with your coarsest grit, move on to a finer grit. Take a pass over the part with 220 grade sandpaper as your next step.
4. Finer. Once you have sanded at 220 grit, proceed to sand with 400, 600, then 1000 grit sandpaper.
5. Finest. Your final pass should be with 2000 grit sandpaper. This is extremely fine and will serve to buff out any remaining sanding marks that are left on your material to give you an extremely smooth surface.
6. Cleanup. Once you have finished all your sanding, you may move on to the cleanup step. Your part will inevitably be covered in fine plastic dust. Use a slightly damp (but not soaking wet!) cloth to gently wipe the remaining dust off your part.
7. Done. You should now have a smooth and clean part that is ready for final use. You may also go ahead and paint your part now (see below)!

Vapor Smoothing 3D Printed Parts

These “Mini-cups” were printed from ABS and smoothed in acetone vapor for 24 hours. A very smooth and watertight finish resulted, but with some loss of feature detail.

Caution: Volatile chemicals used. Avoid exposure, perform in a well-ventilated area, and avoid ignition sources! Safety first.

Vapor smoothing is another very common method of post processing 3D printed parts. The process can be completed with supplies purchased from Home Depot. We will cover the DIY method today but you may also purchase dedicated equipment, such as the Polysher system by Polymaker.

Supplies

• Acetone
• Airtight tupperware container – made of Polypropylene (PP)
• 3D prints (must use ABS)
• Paper towels
• Gloves – Butyl rubber is best but others will be fine for limited direct contact with acetone

Instructions

Start by finding a well-ventilated area. A garage or shop without ignition sources is generally the best choice.

1. 3D Print your parts in ABS. It is important to use ABS for this process. PLA will only degrade in the presence of the acetone that we will use for vapor smoothing.
2. Put on your gloves.
3. Prepare your chamber. Chamber prep is very easy. Start off by wetting your paper towels in acetone. Drape the paper towels over the sides of your tupperware container ~¾ of the length of the paper towel inside of the container and ~¼ of the length outside of the container. When the lid is in place it will clamp these paper towels so they do not slide around.
4. Place parts in the chamber. Put your ABS parts in the container and put the lid in place. Acetone vapors will evaporate from the paper towels and fill the chamber.
5. Start your timer. Set your timer based on how much smoothing you want to occur. A total smoothing time of 1 hour will be the minimum time to start seeing some nice smoothing and 24 hours will be the time when your part will become “droopy”. Waiting longer will help to make your part water-tight as gaps or holes are filled with softened material.
6. Periodically check in. This process is quite dependent on part geometry and size, so make sure to periodically check the parts to ensure you don’t overshoot smoothing.
7. Remove the lid. Once you have achieved the desired smoothness, remove the lid and dispose of the paper towels. This action will clear the acetone vapors. Do not touch the parts yet! The parts will be slightly melted at the moment of removing the lid, so wait 3 or more hours for the remaining acetone on the parts to evaporate away so the surface may harden again.
8. Done! You should now have a beautiful, smooth part that you may not even be able to tell was made with FFF!

Painting 3D Printed Parts

A Master Chief helmet from the Halo series, before and after painting.

Multi-color 3D printers exist today. However, it can be quite difficult to learn software to create a full-color model for a one-off project. Multi-color 3D printers are also generally more expensive than monochromatic FFF 3D printers. So often it will be much easier and more effective to paint your part rather than trying to 3D print a full color model. Here are some steps to avoid some of the common pitfalls.

1. Sand or smooth. To start off, perform the sanding or smoothing method outlined above. Many makers skip the sanding/smoothing step and try to compensate by applying paint to fill in the gaps. Avoid this approach as it leads to excessive paint application which leads to dripping and poor quality results.
2. Prime your part. To ensure that your paint sticks to your part rather than flaking and crumbling off, start by applying a primer. It is very important to pick the correct primer: some primers (such as automotive primer) are designed for use on sheet metal. If you use a sheet metal primer on plastic, then the paint will form beads on the surface rather than sticking to it. These beads will rub right off and you will need to re-sand the part and buy new primer. Get plastic primer!
3. Paint. Once you have applied your primer, you have a surface that is ready to take paint. For this step, you can use spray paint, acrylic paint, or others. I like to use spray paint for my base coat, and then use a brush and acrylic paint to add in details in other colors by hand.
4. Clear enamel. This step is optional but certainly recommended. Enamel is a clear coat that you can brush or spray on which will form a protective layer over your paint job. This will seal in the paint and protect it from getting scratched up and blemished. Once again, for this step, follow the instructions on the can of enamel.
5. Done.