One of the fun parts of turning a bunch of 3d plans… or photos… of freight cars into a model is understanding some of the details of the design. For example, the plans for the W-50-3 Hart convertible gondolas showed some notches in the beams running through the hopper bottom. What were those for?

Some small print on the plans explains it: "5" x 9" removable center sill Dwg. No C-1852". The doors covering the hopper were wood, reinforced with metal strips, and weren't strong enough to support a full load on their own. A thirty foot 5" x 9" beam (or maybe two beams, one stretching to each end of the car) sat underneath, on top of the cross-beams, acted as support for the doors. One of the end drawings also helpfully notes that the sill would be stored behind the doors when the hopper doors were opened.

The engineering drawings for the real cars were filled with little details like this - the use of angle iron on the side dump doors, use of a bolt and a short piece of pipe to keep the door latch from swinging all the way around, and the U-bolts serving as hinges for the side dump doors. Building the 3d model for these cars requires tracking down all those details, and figuring out how to represent the visible ones on the model.

Engineering drawing excerpt from Southern Pacific Common Standard plan C-1652 "Work Car Class W-50-3", in the collection of the California State Railroad Museum in Sacramento. If you're obsessed about these cars as much as I am, call them up and ask about getting a copy of the full plan for yourself.