I was asked recently if I would consider making a 12 Axle, heavy duty flat car as a kit to offer.  I thought, Why not?  It’s unique and it would present a great design challenge.  After a bit of research, I decided on the Kasgro 325 ton 12 Axle flatcar shown here as my prototype.  There’s plenty of photos available on line, plus it’s red!  Who can resist a bright red car?

(Jumping ahead, this is the finished prototype model)

CAD Design:

Using a set of dimensioned drawings, plus many prototype photos, I used ProE to design the car in HO scale.  As it is on the prototype, there is a main body that rests and pivots in the exact center of  two separate three truck bolsters.   The design criteria was that the 15.5” long car had to easily navigate an 18” radius curve.  To accomplish this, I quickly realized that the center truck had to float side to side to enable the bolsters to turn the tight corners without derailing.

I created a computer design mockup of the bolster assembly on an 18” radius curve,  and used that to determine that the center truck had to float 0.110” in either direction.  It was clear that I needed a slot in the bolster, but then I needed something to attach the main deck, the truck and the bolster securely into a single moving assembly.

I found what I needed by looking at electronics supply catalogs:  threaded standoffs for circuit boards.  They were readily available in a variety of lengths, and already threaded for a 2-56 screw.

For the front and rear trucks I chose a 3/16” long hex threaded swaged standoff, and for the center assembly I used a 3/8” round threaded swaged standoff.  The extra length of the center standoff allowed it to attach to the main deck, and protrude thru the bolster to attach to the truck in the center.

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To verify the design, I printed prototypes of the front and rear bolsters, then simulated the deck with a strip of thick polycarbonate plastic.  I added the standoffs and screwed the trucks into place.  I mounted it on a short test track and was glad to see that  the design operated exactly as planned.  The photos below show the center truck floating as the car navigates an 18" radius turn.

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As soon as the design was finalized, I created STL files, uploaded it to Shapeways, and ordered  my first samples.  After a very long two weeks, they arrived.  The material I chose for printing is the “Black Strong and Flexible”  It’s a printed PVC material, and is typically the lowest cost option.  It’s pretty grainy when it arrives, so a bit of sanding was required to make it smooth for final painting.

Weight: 

For the main deck, I knew that I needed to add some operating weight to the car, so I had designed pockets on the underside into which I would add weight.   When the body was sanded and smoothed, I turned the car over on my workbench and filled the pockets with .090” lead shot.  Once I had the lead shot packed down tightly, I mixed a small amount of resin and poured it over the shot to glue it all together.

When the resin and lead shot mixture was dry, I sanded it flat.  The resultant was just over a half a pound of added weight to the car.

Assembly:

Before painting the car, but after sanding, I assembled the entire car to verify that everything did indeed operate as intended.  Fortunately, it did.

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Painting and Decals.

I chose Model Master acrylic “Insignia red” as the color of the car.  Using an airbrush, I applied 5 light color coats to gradually build up the final finish.  The sides were then given a coat of high gloss clear to prepare them for decals.

Decals:  Using the available prototype photos, I replicated the markings using power point.  This file was then converted to a PDF master, which was then used to print an entire sheet of white custom decals.  After applying the markings, the entire car was given two coats of clear flat acrylic.

Brake details:  The brake gear on these cars is located prominently on the top of the decks at each end of the car.  Because each bolster acts as an independent car, they each have their own brake valves and air reservoirs.  For this prototype model, I used a 3D printed valve and air tank from my log car models.  For future models of this car, however, I wanted something more accurate.  I created an all new set of gear with a highly detailed ABDX valve, a two compartment air reservoir, air lines and reserve tank.  This will be printed using Shapeways “Extreme Detail” material.

The final result is an impressive and unique car that operates well in spite of it’s extended length.   For a finishing touch, I’ll be adding a massive auto transformer load, seen in process here. This one will be an MDF core detailed with plastic strip, but I may use it to make a mold for resin copies.

This car was a fun exercise in design and assembly.

As always, I make my designs available to anyone who wants to build one for themselves.  The Bolster assemblies, main deck and brake detail are printed from Shapeways, (about $60 with shipping )  and I'll supply you the standoffs, screws, decals, and brake wheels. ($15) 

The builder supplies 3 identical sets of 100 ton trucks and #48 Kadee couplers. 

Please Email me direct for more information

Dunstan.fandel@gmail.com