I have used Shapeways steel/bronze, just a test-piece to see how it behaved. I made up a replacement part for a large die-cast toy that was my son's favourite, a swivel-steer truck. It had this dinky little fitting that formed the hinge, so it was under enourmous stress and being made of die-cast zamac metal, 'twas hardly surprising it broke. I had to include some close-fitting pins in the new part and not knowing how much to allow for shrinkage or inaccuracy, I intentionally went a bit undersize with my design so that I could drill it out as required. First thing that struck me was the lovely smooth finish of the new part, and second was how incredibly hard and strong this stuff is - while not overly difficult, it still presented a few challenges drilling it out, needing quite substantial clamping and metal-cutting lube because I started out treating it like bronze but it was stalling my cordless drill. That toy truck has survived the attentions of both sons and is still in service, eight years on! I am a mechanical engineer used to working with somewhat exotic materials in the marine engineering industry so I am not easily impressed, and it exceeded my expectations by quite a bit. Screenshot of swivel-steer hinge CAD-rendering attached below.
My preference for wheel centres is still sintered nylon because it is far cheaper, automatically takes care of the insulation issue and is accurate enough that it doesn't require machining, although I will happily admit that setting up tyres and axles to run true is a bit of a fiddle. That said, my first stop is always Slaters' drivers to see if they have something close to what I want. Right now I am trying to turn a static AHM/Riv IHB 0-8-0 into a working model, and Slaters' #7851K driver is almost perfect. When 18 GB Pounds gets you two wheels that screw onto self-quartering square-ended axles, and crankpins, you'd be crazy not to. This steel/bronze stuff would be okay for driver centres except that the economics don't make sense - ordinary brass castings made using high-res 3D prints as masters will cost about the same or perhaps slightly less and require about the same amount of machining but at the same time have much finer detail.
