Sunday, December 6, 2020

A better model dome platform

I have used a variety of approaches in the past to modeling dome platforms, that is, the walkways with railings that surround the expansion dome or the valve casing on tank cars. These were usually floored with wood planks until 1948, at which time steel grid became the norm with the banning of wood platforms (and running boards) for new tank cars. The photo below shows a few platforms; note how small they are, relative to the valve casings (Library of Congress photo). You can click on the image to enlarge it if you wish.

The first approach I tried was to improve, if not actually correct, the grossly oversize dome platform on the Athearn “chemical” tank car. I wrote a fairly complete blog post about this project, which you can find at this link:

The net result is shown below, with the original Athearn part at right and the cut-down version at left, and though the reduced platform size is much closer to prototype, the vertical posts for the handrails are still too fat and too tall. At least I did create a wood platform surface.

     Then I tried using the Atlas part for their kaolin tank car. It has to be cut down to look like a transition-era dome platform, but certainly can be used. The description of the work I did, and the results of the effort, are here: . This certainly produced a right-sized and good-looking dome platform.
     But I was aware that there is an even better approach, which I want to introduce here. Yarmouth Model Works sells an etched stainless steel fret that can be folded into a very nice dome platform, kit YMW-370. You can see it on this page of their web site: . Below is a view of the fret as you receive it. The curving part through the center is the platform frame.

     I bought several of these kits and set about building one. Obviously the first requirement you face is having the right tools for bending etched frets like this. Some varieties of square-nose pliers can work, but by far my best results are from using “The Bug,” as it’s called, a photo-etch bending tool. It’s sold by The Small Shop ( ). 

“The Bug” comes with general suggestions for use. Their advice is excellent: visualize the completed part you are going to fold up. Then mentally unfold it, step by step, to make it flat. The reverse of the order you just envisioned is usually the best procedure for folding.

Although Yarmouth doesn’t offer a set of instructions for the fret itself, they do include that information in their kit for correcting a Semet-Solvay tank car. With the permission of Yarmouth’s owner, Pierre Oliver, I show below the part of that kit’s instructions which is about the fret.

“Cut the platform free from the etching sheet and ream the holes with a #78. Bend the frame in the following order. Most bends are made towards the etched fold line. A pair of square nose pliers will be very useful;
“Bend the platform support tabs.
“Bend the intermediate support legs.
“Bend the intermediate legs down.
“At the corners form the frame into a square.”

At this point it would be logical to make the platform which goes inside the frame. As mentioned, before 1948, these were wood, usually with the planks running transverse or across the car. Evergreen styrene works fine for this. Next you need to adjust the platform to fit your tank car. Here is some more of the Yarmouth directions:

“The platform railings are best formed from 6 separate pieces of 0.015” wire. 2 straight pieces for the end rails and 4 for the curved portions. The platform stanchions have thin tabs that are meant to be formed over the railings to help hold everything into place. Once all is square and parallel, secure in place with CA.”

Below is a photo from Yarmouth, showing a completed platform ready to install. You may notice that  this example has the planks running longitudinal or lengthwise on the car, which unfortunately was not the usual arrangement.

 My first project using the Yarmouth part is for a Semet-Solvay tank car, sold by InterMountain with an accurate paint scheme but lacking the prototype’s dome platform. Below is shown the folded-up Yarmouth platform frame, with its support struts arranged to contact the tank car body, simply resting on the model to show the appearance. The corner posts are not all in final position. Note that the dome walkways on either side of the expansion dome have been removed so the platform can be fitted.

The Yarmouth kit includes the new side ladders, which need to reach from the running board all the way up to the dome platform, so the ladder you see above will be replaced.

I just wanted to show how this looks in progress, and to publicize the Yarmouth part, which I think is very nice. I will come back in one or more future posts to show some completed tank cars with these dome platforms.

Tony Thompson


  1. Great looking work. Roads look a little too new. Too smooth. But I love the signs. And be sure those cattle don't get through that fence!

  2. Thanks for the comment. My layout roads vary widely, from relatively new-looking paving, to old, faded, and tar patched. That's how I think it should be.
    Tony Thompson