Looking around for new curiosities to design in O Scale, I found an old post talking about Conrail's Coil Shield cars from veteran OGR Forumite @Lehigh Valley Railroad. This jogged my memory about a video I had seen online that featured a bedraggled survivor riding behind a modern NS train in Pennsylvania. I did some research and found that these cars were mostly ordered by Conrail from Thrall in the early 1980s. After determining a conspicuous lack of these cars in O Scale, I took on the challenge!
The depressed-center coil car frame is about 52 scale feet in length, which is to say around 13 inches on the tabletop. That's way too big to be 3D printed in a solid piece, so I carefully designed a multi-piece assembly. I went through 3 iterations before I settled on a design that was fully satisfactory. I used the imperfect prototypes to build my personal cars. I didn't want to waste several days of prints, so I spent some time drilling and filling to make them match the final designs.
The "Coil Shield" covers have very distinctive features that stand out from across any railyard. Using my new UV resin printer, I was able to generate the entire coil cover as a 3-piece press-fit assembly. This only took 2 revisions to get right. After I had the cover assemblies printed and slotted together, I glued in some separately applied handrails.
The coil covers have tabs on the underside which press fit into the frame. The final design, which you can see in the back of this photo, was a 4-part frame-- body center, 2 end pieces and 1 floor piece, all glued and screwed together into one very solid frame.
I wanted my cars to be extra detailed, so I studied some prototype photos and designed some trim parts. The brake component details I designed with rivets and high detail for printing in resin. For durability, I decided to make the end platform ladders with my usual sturdy ABS filament. They press into slots on the corners of the car. There are extra mounting holes for a few grabirons and because the two-rail guys always ask about them, yes, NMRA coupler pocket mounting holes.
I spent something like 8 days printing all of the parts for the 2 kits, with all 3 of my printers devoted to the task. While that was running I was able to find suitable decals from K4 to build both a Conrail and a Rock Island car, so that's what I decided to go with. I used some light blue and rust red Rustoleum 2x that I had on hand.
Here are the frames fully painted. The colors are a bit off, but close enough for my tastes. I wasn't sure if the brake air cylinders would interfere with how the trucks fit (since they overlap the truck mounting holes), so I didn't glue them in until the car was fully assembled.
Next I had to paint the coil covers themselves. You have to be very particular not to miss any spots when you paint these, the L-rail structure makes for a lot of paint shadows when you're using an aerosol can.
While all that paint was drying, I set to work on making some trucks. That's right, MAKING them! I made up some modern looking roller bearing trucks with articulated couplers using sturdy ABS filament. It's the same basic design that I've used on many other builds, I just modify the sides of the trucks. I recently acquired a large box of broken MTH trucks so I have an abundance of hi-rail wheelsets on hand.
Decaling the frames was relatively straightforward.
The coil covers were a little trickier since I had to slip some of the decals underneath the handrails.
Here's the Conrail car right after decals. The only tricky part was deciding where to cut the decals to fit them around the ribs on the car's side.
After clearcoating the cars with Matte Clear and letting everything set, it was finally time to put the trucks on. I found that the brake air cylinders were a sufficiently tight press fit that I didn't have to glue them in place, which is handy in case I ever need to take the trucks off for some reason.
Here are the finished Thrall 54ft coil cars on the track!
Another view, this time focused on the Conrail car. I had a tiny bit of metallic silver filament left so I made the trucks in that color just for fun.
Here's a closeup of the Rock Island car next to a MTH coil car. They're big low cars with a nice heavy look to them.
This video shows the cars running on the outer mainline of my layout with the rest of my modern freight cars.
My next project is my most ambitious, a 89ft flatcar with a unique 1970s load. Stay tuned for a future post on that! Until then, let me know what you think about the Thralls and as always, thanks for reading.
