I designed an HOn18 engine sometime back. The shell fits over a MicroTrains mechanism. Link to blog entry on the engine.
These little cars were inspired by George at Show Me Lines Trains in Grandview, MO. He showed me a picture of a side dump car, and wanted to know if I could design and 3D print something similar?
I decided early on to use Micro-Trains Z scale Arch Bar trucks as the standard to design around, and also use their Z scale couplers. These could also be push carts, particularly in S and O scale, and then have no need for a coupler. You will notice that the design closest to the from, has no bottom. I designed it so that I could put a piece of brass bar in the floor to add some weight.
Once I figured out the dimensions and shape needed to fit the trucks and couplers, I took those designs and started trying other options using the original base.
I used .030 styrene for the connector between the tipper and the rest of the car, and thus the tippers will actually tip, as long as you only glue the styrene rod at one end.
I am sure there are many more possibilities, and I am sure I will come back and do more in the future.
As I mentioned above, it took several redesigns to get the trucks to fit properly.
Here are several early attempts. I am never going to get a completely clean angle with and FDM printer, but it only took a little filing to get it looking reasonable.
This kind of give you an idea of how many failures I had, just getting a square box on wheels.
This is a good example of the layering making the item, in my opinion, unacceptable. Note the layering on the corner boards. It makes the "grain" run the wrong direction, horizontally, rather than vertical. In subsequent designs, I left off the corner boards, and added styrene strips.
A couple of things to note. The bottom gondola has had the brass bar inserted for weight. Also, the corner boards on these gondolas are styrene strip, which looks much better than the printed vertical boards. The side dump cars, several different versions, various stages of completion, natural ABS, and primed.
I painted the side dump cars with Sophisticated Finishes Rusting paint. The gondolas were painted a wood color then a wash of India Ink and Alcohol.
The trucks were installed using the Micro-Trains pin provided with the trucks. As I recall, I used the 2-56 tap drill size as the hole for the pin, and it worked great (there does seem to be some variation in the pin diameter). The couplers were installed using the screws provided with them.
Here is a shot of the engine and cars sitting on some Micro-Trains Z scale track, a penny to the right for scale reference. Again, these could also be used in S and O scale for push carts.
Some mining inspiration, a blog post of from several years ago from the salt mine and museum in Hutchinson, KS.
And from the Helper, UT Mining and Railroad Museum.