Friday, February 20, 2015

Building an On18 Locomotive: Part I

Calico Gold Company #2, the Walter Knott, fresh from the paint shop and on its way to the CGC facilities for final outfitting. Building this little On18 mine locomotive is the subject of today's post.

Before I start building benchwork and laying track on my On18 Calico Gold Company layout, I wanted a relatively simple On18 locomotive to pull some trains with. After doing a little research, I decided on a vertical boiler design that starts with a 3D printed shell from Tebee Models at, atop a smooth running and reliable Kato 11-103 drive unit. This is my first real build in On18 and my first time using 3D printed parts. Despite the learning curve, the little steamer is coming together quickly.

The two axel Kato 11-103 drive unit is 2.125" long by 0.6875" wide. I'm using my N scale Pagosa & Southern switching layout as a test track.

The 3D printed shell from Tebee Models is made from polyamide nylon, what Shapeways calls their "White, Strong and Flexible Plastic." It is white and strong, but comes unfinished with a rough, sandpaper like texture. It fits perfectly over the Kato mechanism.

My first modification to the shell was to add a new stack. I cut off the top of the cap-stack on the printed body and replaced it with a taller HO diamond stack and some plastic tubing from my scrap-box. Here the new stack has been painted with grey primer. It's a snug press-fit over the original stack.

I'm not planning on adding a decoder to this tiny model so I filled the hollow spaces of the boiler and water tank with about 1.5 oz of BBs for additional weight. I mixed up some 2-part epoxy resin and carefully poured it over the BBs to cement them in place. I wanted to do this before painting the shell so any spills could be more easily cleaned up or covered. I let the epoxy cure overnight before going on to the next step.

The next challenge was to smooth out the rough 3D printed surface and make it look more like metal. Conventional wisdom says this should be done with primer and repeated sanding but I was concerned that too much sanding would wear away the details. Acetone vapor smoothing has been recommended for 3D printed parts but that only works for ABS plastics and not for polyamide nylons. I found a technique online for using several coats of plastic primer to smooth the surface so I decided to give that a try.

First I cleaned the shell thoroughly with a wash of 70% isopropyl alcohol. Next, I took the model outside for painting using Krylon Satin Finish Plastic Primer. Several coats are necessary because the surface is so porous. A second heavy coat was applied 20 minutes after the first. Then a third coat was applied 30 minutes after that. A fourth coat was applied an hour later and a fifth coat about 5 hours later. After drying for 24 hours, the shell had taken on a smoother, cast iron appearance.

More or less satisfied with the smoother surface, I masked off the black areas an sprayed the tank and bunker with satin finish Hunt Club Green. This is the "official" green for all CGC equipment.

Diving back into the scrap-box I was able to find the shell of an old MDC HO Consolidation and cut the smoke-box out from the backhead with a razor-saw. Then I wrapped some 220 grit sandpaper around the barrel of a marker and sanded a curve into the back of the piece so it would snug up to the boiler. The next step was making a new throttle from a paperclip and drilling a #61 hole above the firebox to receive it. The paperclip/throttle was ACC'd into place and the assembly painted flat black.

While I still had the flat black paint out, I masked off the green water tank and bunker and gave everything else a coat of the flat black to dull it down.

Looking at some photos online of similar historic locomotives made me want to add some brass bands to the boiler. These were cut about 4 scale inches wide from very thin sheet brass. I taped them down at the ends and sprayed one side with 3M 45 All Purpose Adhesive. After letting this set up for several minutes to get tacky, the bands were then applied to the boiler like tape, with just a small drop of ACC to keep the ends from curling up.

With the brass bands in place, the firebox and throttle assembly were glued to the boiler with thick ACC.

After looking long and hard at the model, I came to the conclusion that the stack was too tall. As a fellow modeler pointed out (thanks AJ!), a mine loco working in low clearance tunnels would likely have a shorter stack. So I went back and cut a scale 12 inches from the height and I'm pleased with the less cartoony look. I was also curious to see how well decals would adhere to the "smoothed" 3D printed surface so I went ahead and applied Walter's numbers and nameplate. A couple drops of Micro-Sol really helped the decals snug down onto the surface.

At this point, the Walter Knott is starting to look less like a collection of parts and more like an elegant early steamer. There are still many details to add: steam pipes, gauges, a headlight, bells and whistles, and link and pin couplers among other things. I also need to decide on whether to add a cab or not. There is much more still to be done but it will have to wait until more parts arrive. That's going to wrap it up for this time. Thanks for checking in, amigos. Adios for now!

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