For most printing, PLA especially, there's no risk. Some people will find the odors from ABS and ASA to be problematic.

For the idler project, consider that you can create a CAD type drawing and issue it to Shapeways or SendCutSend and have a part machined from delrin or nylon. Delrin is pretty strong stuff and machines quite well. It's important to get the measurements correct, though, as each iteration can be expensive.

That's one aspect of 3D printing; I can create as many models as needed to get a correct fit and it cost only pennies in filament, but oodles of hours.