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Bits to Atoms: Building the Millenbaugh Motivator, Part 5

By Sean Charlesworth

Sean recaps the finishing and detailing of his Motivator project. The tricky part: making his 3D printed parts look like metal.

After three months of work, the Millenbaugh Motivator has been completed and the parts have been delivered. As Adam has demonstrated before, finishing is extremely important and he immediately got to work on the Motivator parts in order to detail and finish it along with his Mecha-Hand for Comic-Con. There were some difficulties with the crankshaft due to tight tolerances and the addition of paint, but I’m working on a revised version for him to use later.

Adam's painted Motivator.

Now that I delivered everything to Adam and am back home, the only thing left to do is the finishing work on my own Motivator! And to be honest, this is the part that I’ve been kind of dreading. This goes way back to when I was a kid and built a lot of models. I would be super meticulous on all the details, get to the very end, and ruin the final paint job--every time. This has stuck with me and almost every time I work on a project, I get to the end and often peter out, leaving it unfinished for long stretches (or sometimes forever). In hindsight, I just didn’t have the right tools or know the right techniques for finishing work. I’d spray paint when it was too humid, too cold, too windy, too dirty, using crappy paint or my really bad airbrush setup. I had a subscription to Fine Scale Modeler magazine and would constantly try higher-level techniques before I understood the basics which almost always ended poorly. In the end, I just thought I was really bad at painting and finishing and it subconsciously kept me from finishing or even starting many projects. I still haven’t fully painted the Stormtrooper Blaster I made five years ago!

My still unfinished Stormtrooper Blaster - weathering would really help.

I decided to not screw around with the Motivator and just finish it, but I wasn’t sure how. On the trip to San Francisco, I’d hope to do some painting and finishing with Adam but we ran out of time. I did pick his brain about it and we tossed a few options around. Early on, while I was still building the Motivator, Adam was seriously considering metal plating the whole thing and asked me to look into it. I called just about every place in NYC and surrounding area and didn’t have much luck. Coating plastic, or electroplating, is done all the time--it requires the plastic to be coated in a conductive paint, which the metal plating will adhere to. It seemed like most of the places that do this work usually plate metal and they either didn’t do plastic at all or were reluctant to do so and they didn’t really want to do small jobs such as the Motivator. In the end, Adam decided to move on and figure out a different approach.

ALCALAD metal finishes. CREDIT: ALCLAD

I had been doing my own research and found ALCLAD, a metal paint system that looked absolutely amazing but required an airbrush setup and skills which I didn’t have. I have never produced a satisfactory metallic finish with spray paint so decided to try Rub ‘n Buff since Adam and The RPF have mentioned it many times. Rub ‘n Buff is a wax-based paste with metal particles suspended in it and, once applied, it can be buffed to a shine, unlike most paints. It’s readily available at just about any art or hobby store, cheap, relatively low-key health-wise and easy to apply (in theory).

Rub 'n Buff on ABS and on ProJet plastic.

The NYU print lab was kind enough to give me a scrap piece of plastic to experiment on and I also used some of the black ABS I used for the top plates. It seemed simple enough: apply the Rub ‘n Buff, wait a while and then buff it to a shine. I like how it was looking on the black plastic vs. the white--I felt that where the black peaked through made it look more like real, weathered metal. I needed to do a little clean up on the 3D printed parts since there were some ridges from printing--even with high-resolution parts you can get stepping, which is where you can see the layer transitions.

White parts painted with Krylon Fusion black.

The resin used in the ProJet printer is easily sanded and painted like any other plastic so this wasn’t an issue and only required light sanding. During my tests I also discovered that if I hit the surface lightly with a scotch-brite pad before applying the Rub ‘n Buff it gave it a brushed-metal look. I painted everything with black Krylon Fusion spray paint which is specifically formulated for plastics and requires no priming - turned out great. Next came the silver Rub ‘n Buff - which turned out terrible. I had a bad time with it - either it would not lay down evenly or clumped up in blobs and I really messed it up by trying to put on a second coat. All my tests had turned out ok but they were mostly small patches - covering large areas was not going well. Luckily, the Rub ‘n Buff came off fairly easily with some alcohol but I needed to figure out what I was doing wrong. My technique was to apply it using a small square of cotton rag, let it dry for a while and then buff it to a shine but this wasn’t working on the large parts. Once again, The RPF to the rescue--I found this armor video by Arturo Delgado that made everything clear:

Making armor with Rub ‘n Buff (application at 4:15) Credit: Arturo Delgado

Following the advice from the video, I ditched the rag applicator and literally got my hands dirty by applying the Rub ‘n Buff with my fingers. As messy as this was, it really worked, as it allowed me to apply it in a very thin layer that worked into all the nooks and crannies and body heat and friction melted the wax just enough to make it really stick. It was also important to let it dry for a few hours so the wax could harden in preparation for buffing. I lightly buffed the parts with a cotton rag and it was starting to look really good. I got a little carried away at times and the black paint started to peek through but, as I hoped, it just made it look more like worn metal.

Rub 'n Buff unpolished - polished.

So far so good, the Motivator was looking as close to real metal as I could get it, but now for the part I always put off: weathering. The valve arms had a weathered bronze-look so I started with the black spray paint and then used antique gold Rub ‘n Buff and a small brush to highlight the edges--this turned out great and gave me hope for the rest. I added some green patina as well and planned on using some acrylic paint to add some rust and other grime. Didn’t think this one through; the wax-based Rub ‘n Buff repelled the water-based acrylic paint, just like a newly waxed car. I also tried some enamel paint, which dissolved the Rub ‘n Buff. Oops. Eventually I found that leaving the paint thicker by using less water got it to stick ok and the Motivator was starting to look nice and worn. I also used some india ink for stains and black shoe polish that worked really well to simulate built-up grime and gunk around parts.

I also needed to weather all the brass parts but wanted to make this look really legit and age it for real. Googling ‘brass weathering techniques’ led me to a Pirate forum of all places where I found thorough instructions--all in pirate-speak. Techniques included soaks in various liquids such as salt water, ammonia and vinegar, but none of these worked very well. I ended up using Birchwood Casey Brass Black, a chemical typically used for blueing and blacking gun metal. This worked amazingly well and produced the exact look I wanted in seconds and after a little steel wool and green patina, it looked perfect.

Brass aged with Birchwood Casey Brass Black

The last detail were the hoses, but I didn’t have all the needed parts. I had already specced the hose barbs that mounted on the block and Adam gave me the large plastic connector for one end and some braided sleeving but I needed the rest. I ended up getting brass air fittings for the other hoses and a super-flexible PVC tubing for the inner hose. Since my Motivator will never be attached to a full Mecha-Hand and probably be displayed in a cabinet, I shortened the hoses to make them more manageable. The problem I ran into was even with the super-flex hoses, I couldn’t pose them and they would tend to spring open and push the Motivator around. I solved this problem by inserting an armature wire in each hose, so they could hold a pose.

Finished hoses
Armature wire added to hoses to hold pose.

Considering that I had never attempted a Rub ‘n Buff finish and with my long history of choking on the finishing work, I am extremely pleased with how this turned out. I also realized that I really like working on ‘used’ items, not only because they look cool, but there’s more leeway on the finishing--although a bad weathering job can be just as ugly as a bad finishing paint job.

Adam gave me one of the plaques he had made for the Mecha-Hand, which gave me a good idea of how to display my Motivator, sans Mecha-Hand. I need to gather materials and do some work for this display, but it’s gonna be pretty cool. I’ll make sure to post an update whenever I get it finished.

Thanks for coming along on this adventure, you’ve all been very supportive and kind during my work on this project--it’s part of why I like our community so much. I’ll be on hiatus for the next few weeks, but stayed tuned for the next 3D printing article: a Halloween special!

In case you missed the other installments of the Millenbaugh Motivator build recap: