Scratchbuilt SD40-2’s

Progress so far on one of two SD40-2’s I’m scratchbuilding.

I’ve been waiting all my life (and very patiently I might add) for a high quality HO SD40-2 with the correct bolster spacing. The Kato models come close, but it’s hard to find undecs and I’ve come to discover that they aren’t terribly easy to modify. Railflyer is another option, but their models are at least another year away and I need something to keep my busy now… So, I’ve started scratchbuilding my own.

The donors.

Two undecorated Athearn SD45-2’s gave their lives for this project. For my units I’m using the frame, drive and trucks, the DB blisters and some of the details. The frames have been heavily milled to get them close to scale width.

P:87 42” wheels by NWSL.

Since I like to frustrate myself with P:87, the Athearn wheels had to go. They were replaced with 42” scale profile wheels from NWSL. While I was waiting on the frames to be cut (I don’t have a mill, so I shopped that portion of the project out) I painted and weathered the wheels following a technique that Brian Banna outlines here.

The key fuel tank components prior to final assembly.

While the Athearn fuel tanks are very nice, they were going to need modification to fit on my newly “narrowed” frames. Since they are missing some features that I like (mainly the contoured underside of the prototype) I decided to use Railflyer tanks instead. To do so, I cut an opening out of the top and made a baffle on the lower part so that I could fill the empty space with lead shot for added weight. The Athearn tanks were shipped off to a new home with a fellow modeler who will put them to good use.

A completed fuel tank.

Once I glued the two halves together, I attached the photo etch. The end sheets don’t need any modification, but I had to make two parallel cuts on the top plate to accommodate the hole I had carved out of the plastic.

The original Athearn SD45-2 frames.

In order to use the frames, they needed to be no wider than the frame rails. Therefore, everything that would reside under the deck had to be removed. I also needed to cut some material off the underside of the motor mount area so that it would fit inside the Railflyer fuel tank. Some notches were also cut at the front and rear to accommodate styrene blocks on my scratchbuilt decks, these serve two purposes, they help to align and “lock” the deck in place and they allow me to model the pilot braces which would otherwise be impossible if I ever wanted to disassemble the units for maintenance (a seemingly important consideration). I also had all the vertical projections lopped off since they would either have been sticking up through the deck due to the 40-2 hoods being of different dimensions to the 45-2 hoods, or would interfere with the placement of interior components (like speakers, decoders, etc). Finally, I filled the openings that Athearn had used to mount removable weights with a moldable epoxy/metal product called “Propoxy 20” this stuff cures as hard as metal and is drillable, machinable, sandable, etc. This made the frame considerable stronger once it was cut.

The deck.

The decks were created from a sheet of 0.040” thick styrene. This provides the necessary rigidity, but is unfortunately too thick to mount the air tanks at the proper vertical distance from the fuel tank. To solve this problem, rectangular notches were cut into the sides of each deck and filled with sections of 0.020” thick strip. The thickness differences will be hidden by the sills.

Air tank mounting locations.

The air tank mounting areas were attached and braced with sections of 0.020” square styrene strip. Holes for the Railflyer air tank mounting pins were drilled before installation using a homemade jig. Next I attached the frame “rails” which are 0.030” x 0.125” strip. These make the deck considerably more sturdy and precisely match the height of the Athearn frame.

Major components so far.

I now have all the major components done. Since this photo was taken the horizontal portion of the frame rails have been added to each deck and the holes for the traction motor pillow brackets have been drilled using a custom template I made. I also added mounting surfaces to the stepwell notches on each corner of the decks, these will allow the top plate of the brass Railflyer stepwells to sit flush with the top of the styrene deck (they will then be covered by treadplate). That’s it for now. These will be on display at the 9th annual New England Prototype Modelers meet coming up next weekend (June 3-4) along with a few other projects.

Chris