As is evident from the handout I posted to this blog a month or so ago, I gave a new talk at the Cocoa Beach “Prototype Rails” meeting on wine tank cars (see it at this link: http://modelingthesp.blogspot.com/2017/01/handout-for-wine-tank-cars.html ). One of the topics I spent some time discussing in that talk was the numerous tank cars in wine service which had been converted from their as-built single-compartment design, to three-compartment cars. This was readily done by removing the tank heads (the curved end pieces of the tank), placing two pairs of similar bulkheads inside the tank to make three compartments, and then putting the end heads back on, along with an insulating jacket. Shown below is a sketch of the final car interior (based on a sketch by Richard Hendrickson).
The most obvious indication that a tank car has been converted in this way is that the expansion domes on the two new compartments are smaller than the center dome. This is because the size requirement for these domes was that they be at least as large as 2 percent of the volume of the
compartment on which they were placed. The original dome was that size for the entire car, while the new domes only have to serve a smaller end compartment. Shown below is a prototype General American wine-car example, GATX 1095. (Hendrickson collection)
Note in this photo that the car has frangible-disk safety vents atop each dome, instead of safety valves. I discussed the use of these vents, and showed the correct model parts, in a prior post (you may read it at this link: http://modelingthesp.blogspot.com/2017/01/frangible-safety-vents-on-tank-cars.html ). The auxiliary domes also have flat tops made from steel plate.
I wanted to try and model one of these cars. The first thing to do is to estimate the various dimensions of the car as you see it. This is relatively easy, because we know the wheels are 33 inches in diameter. Measuring a wheel then gives you a scale number to convert all other desired dimensions. When I did that with this particular car, it turns out to have a tank which is 34 feet long and 78 inches in diameter, a center dome which is 55 inches in diameter, and end domes which are 50 inches in diameter. These proportions could be used to model cars that would have different sizes than this car.
I know that this is a 6000-gallon car from looking it up in the Tank Car Capacities Tariff (for more on that essential document, see my post at: http://modelingthesp.blogspot.com/2016/12/the-tank-car-tariff.html ). Specifically, its three compartments are almost equal in size, at about 2000 gallons each (adding up to 6089 gallons). But cars of other sizes were also converted in the way shown in the prototype photo above. I decided to make a stand-in model of such a car.
I began with the former Proto2000 insulated tank car, a 10,000-gallon car, more recently available from Walthers. This model represents an American Car & Foundry Type 21 tank car, and its tank diameter is 96 scale inches (about 1.1 actual inches). The dome has a diameter of 64 inches, or 0,734 actual inches. Choosing a smaller dome diameter, in accord with what you see in the prototype photo above, I chose to use Plastruct 5/8-inch tubing, which translates in HO scale to 54 inches.
My first step was to grind the ends of the Plastruct tubing to match the 1-inch tank size, for which I used a piece of 1-inch tubing. Wrapping abrasive paper around the 1-inch tube allows quick and easy grinding of the end of the Plastruct dome tubing. I usually start with 60-grit paper, and then go to 150-grit paper, as shown below.
Almost sooner than I can describe it, usually in a minute or so, you get something like this:
Next, I determined how high this dome would be. Since the main dome in the prototype photo above is about 22 to 24 inches high, I chose to make the subsidiary domes half that height (compare the prototype photo), or one scale foot. That height is the minimum height from the tank top. A quick calculation using the formula for a cylinder shows that such a dome would contain over 120 gallons, well in excess of the 2 percent requirement for an credible-size end compartment in a converted tank car. I made two domes 12 scale inches high.
As I noted about the prototype photo of GATX 1095, the auxiliary domes have flat tops, not hemispherically-rounded tops like the main dome, and the top plate overlaps the sides. This is easily made from sheet styrene. I simply traced the end of the 5/8-inch tubing onto some 0.015-inch thick styrene sheet, cut out the disk a little oversize with scissors, and carefully used a flat file to reduce the size to the traced outline. As the material of the Plastruct tubing I used is butyrate, I cemented each segment of tubing to its styrene top with Plastruct’s “Plastic Weld” adhesive.
Here is a test fitting of the two new domes to a Walthers tank car (not the car I will eventually use), just to show the dome size relationships:
Next I will add approved bolted manways, one source of which is the Tichy detail set, and the Owl Mountain frangible-disc safety vents (my post about these is cited above, just under the prototype photo). Then, of course, painting and lettering. But all that will all be shown in a future post.