Machine Simulation

I'm not able to get my machine parts to show up in the simulator. I've created STL files for the table and fixtures/work holding and I'm using a default spindle head stl. I've verified the STLs are in the correct units (inches). I select the files in the machine parts in the tab and save the machine. For now I'm just trying to get 3 axes working, I'll add the 4th later. When I generate a toolpath and simulate with the "show machine parts" checked in the simulation options I get no machine parts shown. The help file and 5 axis machine setup video doesn't go into any further detail. Is there a more detailed guide somewhere? Do the stl files need to have a specific origin or something?