When you model something that has been gone for over a hundred years, you get used to squinting at photographs and trying to imagine a design that might present similar patterns of dark and darker. In the case of the engine truck, which is missing from the erection drawing for 622, I found a drawing online that explained the shapes beneath the cylinders. I used that for a source.
Of course, what makes railway modelling interesting is that the design not only has to look good, it has to be something I can actually make and also it has to function. In this case, I’ve decided to give up on independent bearings in the engine truck, and run the axles through polished holes instead (let me know if this is foolish). I also want a way to feed power from the axles through the kingpin (a 1-72 screw) to the frames of the locomotive, and so, I’ve devised a way to present a top and a bottom of the bolster that are electrically isolated from one another, while flexing to allow the wheels to equalize.
At the same time, I was figuring out how to make OnShape produce drawings that I can import directly into InkScape to drive the etching process. It’s all taken a couple of days, but I think I’m there now, and productivity is set to increase. Here, for example, is the drawing for one of the truck sideframes.