Alright! Finally, I’ve uploaded a model successfully. I continued to struggle with inverted normals until I figured out how to get Accutrans to fix the remaining normals. The do-it-yourself active worlds page came to my rescue when the Accutrans help files failed to load, and it turns out all you need to do is click on a couple of semaphore flags, then click on the model.
Once that’s done, you just have to save it as a Collada (.dae) file again. Unfortunately, somewhere along the line, the model got expanded a hundred times; it also seems to lose its units. As Shapeways interprets such files as cm, the resulting model was 778 cm long (about 25 feet for those of you who remember those). That’s a bit too big for the Shapeways printers, and a bit too big for HO too.
Fortunately, Accutrans knows all about scaling, and so, all I had to do was to save it at a scale of .0254, and I got a part that ought to work.
As you can see from the screenshot, it’s apparently only going to cost me $10 to print the side, which means that the whole model might come in well below my original $100 estimate.