I've started casting mine car parts. While it looks like a lot of unassembled cars, out of the 11 castings, only about 6 are satisfactory.
The hardest parts to cast are the "steel frames", because the brackets are so tiny and fragile, they'll either break or resin won't get in the mold at all.
For those of you unfamiliar with the anatomy of the mine car, the wheels are mounted onto a rigid steel frame. This frame has 6 brackets, 3 on each side that bolt onto the wooden part of the car, which the main body where the passengers sit. While the prototype has its wheels on the steel frame, mine are actually standard HO scale wheel truck that snap onto the bottom floor of the car; the steel frame is just for show, but it's an important detail.