Stratasys’ PolyJet 3D printing technology can produce some amazingly detailed parts that can mimic a wide range of rigid and flexible materials – even full-color and transparent parts. With some simple post-printing steps it is easy to obtain a stunning high gloss finish on even the matte surfaces of PolyJet parts. In a previous overview, we showed you how to clear coat complex shaped parts to obtain a gloss surface without any sanding or polishing. In this tutorial, I will show you how to create high gloss, even optically clear finishes, on parts the old fashioned way, with some elbow grease.

Using Sandpaper for Smoothing PolyJet 3D Printed Parts

Before we begin, here’s a list of what you’ll need:

• Dust mask or respirator (I always play it safe, if I am sanding anything, I wear a mask)
• A small tub of water (I use a food storage container)
• Sandpaper (500, 1000 and 1200 grit)
• Heavy scratch removing plastic polish (I use Novus #3)
• Fine scratch removing plastic polish (I use Novus #2)
• A soft towel (for clean-up and polishing)

The first order of business is sanding the surface of the part to a very smooth even surface, this is done with the 500-grit sandpaper. Because we are working with a plastic, it is wise to “wet sand,” this means we will be dipping our part and our sandpaper in water every ten seconds or so. Wetting the paper and our work will prevent the part from heating up from the sanding process and prevent the sandpaper building up too much plastic residue – both of which would prevent the sandpaper from evenly removing material from the part. This first step is the most important, think of this a preparation for all the following steps, if you skimp here – you will never have a good polished part.

Because we were so thorough with the 500-grit, the next steps are much faster. We now need to go to the 1000-grit sandpaper and wet-sand away the fine scratches left by the 500-grit. Remember to keep the sandpaper and your work wet to help the sandpaper do its job. Periodically wipe the part dry with the towel and inspect it to ensure you have an even matte surface. When you are satisfied with your progress with the 1000-grit, move to the 1200-grit and repeat until you have a smooth almost velvety matte surface – you shouldn’t see any deep scratches or imperfections. If you find a small imperfection, work the area with a fresh piece of 1000-grit and then back 1200-grit again.

Polishing PolyJet 3D Printed Parts

You can now set your tub of water aside, you will just need your plastic polishes and your towel (if it’s too wet grab a dry one). Once your work is dry, apply a liberal amount of Heavy Scratch Removing Plastic Polish to the part (shake well as some brands may settle and separate). If you have never used a polishing compound (also called a rubbing compound) before, simply think of it as liquid sandpaper. Instead of grit being adhered to a sheet of paper, polishing compound has grit suspended in a liquid – essentially making it an ultra-fine grit sandpaper liquid.

As you buff it onto the surface and rub it into the part, you are sanding away an ultra-thin layer off the surface of the part. I recommend applying moderate force and working the towel over the part rapidly in varied directions and in circular motions if possible. You will most likely need to apply the polishing compound several times over the work as it quickly gets absorbed into the towel and it also begins to dry on the part. After a minute or two of polishing, buff the area with a clean dry towel and inspect your work. The Heavy Scratch Removing Plastic Polish should leave a very smooth satin finish, not quite glossy, not quite matte, but it should be very smooth. This process can be repeated if necessary, to ensure that you have an ultra-smooth satin finish.

Lastly, move to the Fine Scratch Removing Plastic Polish and get to reveal the fruits of your labor. Apply a generous amount of polish and buff the part the same as you did with the Heavy Scratch Removing Plastic Polish except it is very important to not use the same part of the towel that we used previously. The towel will pick up and hold the grit from the previous coarser grit polish and prevent you from getting a high gloss finish, so use a clean portion of the towel. At this step, you should try and focus on keeping small circular motions as much as possible while buffing with the towel – working your way systematically around the part as to not miss any areas. Wipe the part clean periodically and inspect your work, repeating until you have achieved the desired level of gloss.

There you have it, a high gloss part without the need of clear coats or waxes. While this process is more labor intensive, it produces a part that has a lasting hard surface that can’t chip or flake over time. These steps also apply to any hard plastic, not just Stratasys PolyJet 3D printed parts, so the next time you are looking at your old foggy car headlights, you now have the skills and materials to make them look like new. If you have any questions on how to finish your PolyJet or Stratasys FDM parts, please feel free to reach out to TriMech’s 3D Printing Applications Engineering team.

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