I have been playing about with Fusion 360, one of thrings you will need to include before very long is a fixing, even if you can 3D print everything in your design at some point you will want to stick two parts together at which point you will need a bolt or a screw. 

This took me a while to find in Fusion 360 as it is not a work flow that instantly jumped out as how it would work. I also for a fair while thought about drawing my own bolts, but I reasoned that someone else must have done the drawings first.