Guides

Guide: How to Finish 3D Prints

While I have 3D printed hundreds of designs over the years, not once have I taken the steps to finish a single print. There are plenty of videos and articles covering the process but they are often a general overview and leave out small but important bits of information. For someone inexperienced like myself who prefers to follow explicit instructions, the artistic process can be a rather daunting task. Unfortunately I purchased my 3D Printers for costume and prop design and can’t leave them unfinished forever, where this guide will cover my successful, albeit awkward adventure into the task of post processing 3D prints.

As a side note, products such as XTC-3D or Alumilite Clear Cast can drastically reduce the overall work involved. These are 2 part resin based epoxies that will fill layer lines and smooth the surface, alleviating the need to sand and fill defects. I personally however wanted to experience each step of the process and opted for the more labor intensive route. For those of you that aren’t masochists, these may be a more appealing solution.

Purchased Parts

Rustoleum Filler & Sandable Primer - $4.97
Bondo Glazing Spot Putty - $14.58
Assorted Grit Sandpaper - $6.99

Rustoleum Gloss Black Paint - $4.94

Krylon Metallic Chrome - $4.81

Printed Parts

Immortal Warrior Mask – $14.86

Overview

As the foundation, I chose a complicated yet impressive design that I felt had great potential. The Immortal Warrior Mask from the movie 300 has a beautiful yet ominous look, with deep curves and smooth lines that make the features more prominent. Better yet, it also has a worn chrome finish that I wanted to try and capture using spray paints.

This particular design was unfortunately too large for my 3D Printers as a single print, where I opted to slice the model in half right below the nose. As it was printed in two parts, I used Loctite Ultra Gel Control to cement the halves together. This created an extremely strong bond between the pieces, although somewhat noticeable and requiring additional work to smooth.

 

Instructions

To get started, I decided to first cover the entire surface with Bondo Spot Putty in order to fill the layer lines. Since the putty begins to dry and crumble quite fast, I focused on small areas by squeezing a blob on the surface and smoothing it out with my fingers. Wood Filler is often the recommended alternative, however I found the Bondo Spot Putty fun to use and quite easy to manage.

After the putty had cured, I wet sanded the entire surface down using 200 grit sandpaper. Bondo’s dark red color contrasted well with the orange PLA used for the print, emphasizing all of the gaps and divots that were filled in the process.

 

Once I had a relatively smooth base to work with, I sprayed 3 light coats of Rustoleum Filler & Sandable Primer, spaced about 15 minutes apart. The primer filled any remaining defects, especially in the hard to reach areas such as the creases around the eyes, nose and mouth. My initial coats of primer did not spray well, resulting in a less than ideal surface but still good enough to move forward.

I noticed at this point that the seam line between the two halves was still somewhat pronounced. I went back to work with the Bondo, repeating the same steps as before to smooth out the ridge. Any surface defects visible at this point will be seen in the final coats of paint. As such, repeat the filler and primer steps as many times as necessary until you have eliminated such problems.

 

I repeated this process several more times until I was satisfied with the results. After wet sanding down the last application of Bondo with 200 grit sandpaper, I applied two more thin, even coats of primer before moving on to the next stage.

At this point, the monotonous prep work was finished and I proceeded to wet sand the entire mask. This time I started with 400 grit, followed by a finer 800 grit sandpaper. While 400 will be sufficient for almost all applications, higher grit sandpaper will provide an extremely smooth surface. I was extremely pleased once finished, where the mask had a near glass like exterior.

 

When researching how to achieve a chrome finish with spray paint, no one ever came close to the real thing. Dozens of Youtube videos tried, yet often ended up with lackluster results. As I am too poor to buy a chrome plating kit and too impatient for electroplating, I decided to try it myself using a variety of options from the local hobby stores instead.

To test out each of the potential candidates, I 3D printed apples from Thingiverse to compare the results of each can side by side. For the most accurate outcome, each apple was hit with 3 light coats of primer, followed by 2 coats of gloss black paint. The Krylon Premium Metallic Original Chrome was by far the best option available, where the rest were either dull or not even close.

 

When it comes to chrome, one thing is for certain though, a gloss black base is an absolute necessity. The chrome paint should be applied in light coats over the gloss black, where this is what gives it the more reflective surface.

With this in mind, I went ahead and sprayed the mask with two coats of Rustoleum Gloss Black, spaced 24 hours apart to allow for sufficient drying time. While the first coat went on smooth, spider webs formed in several areas, likely caused by the paint being sprayed to thick. I did a light sand in these spots with 800 grit sandpaper to smooth it out as much as possible prior to the second coat being sprayed.

 

Satisfied with the progress at this point, I decided it was time for the final coats of spray can chrome. With my fingers crossed, I laid out my makeshift paint booth, vigorously shook the can and laid the last coats of paint. While one pass was almost sufficient, several of the hard to reach areas were missed and a second time over those gave complete coverage.

Final Thoughts

While my results weren’t perfect, I am very pleased with the outcome. The preparation phase is extremely important, sanding and filling any defects before you move on to painting. As I noticed with the seam line, imperfections will absolutely be visible in the final coats. As such, it is advised to repeat that stage as many times as necessary until the blemishes are gone. In this case, another application of Bondo on the seam would have likely brought this much closer to a perfect finish.

I was however extremely impressed by the Krylon Premium Original Chrome, where this came much closer to an actual chrome finish than any other paints. It has a nice balance between metallic and reflective and captures the look of the original mask almost perfect. While I am not sure if the gloss black base is as important with spray paint chrome, I do feel it improved the surface quality and appearance overall.

3D Printed Mask Finished

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