Gerry, where I can, I'm downloading the machines from the SketchUp 3D Warehouse. That said, none are ready for printing. They either have lots of reversed faces which the slicer and STL convertor can't recognize, they have parts that are too thin to hold together even though the printer will resolve them, or they have incomplete structures that must be closed to be recognized as a "solid".
I'm also drawing my own. The radial drill was completely drawn by me. And I'm working to create a good 1:48 scale model of an EMD 567 Prime Mover. I've got the heads and block complete. I'm working on the complicated front end with all the pumps and piping, and wrestling with the Roots Blower assemblies that grace the back end. I've gotten the Blower drawn nicely, but the plenum below it is a killer. It's got curves all over the place and intersecting planes and then it has the egg crate ribs on the outer facing side. I could more easily hand form it in Milliputt, but I want to be able to print it and possibly make it available for others. I'm sure it can be drawn, I'm just not so good at it.