Building a Delta Robot: 3D printed joints

The green is one half of my first attempt.  The two on the right are attempts 2 and 3.  The assembled joint in the bottom left has an M3x20 screw and a 1/8 ID, 3/8 OD bearing.  In every single case the round part that holds the bearing cracked when I inserted the bearing.  In each case I increased the size of the hole.  In the last version I tried to file the inside edge and even smooth it with a drill bit.  While 3D printing is great for proof of concept I don’t think the makerbot is up to the levels of accuracy I’m going to need from these joints.

I wonder how it would do with shaft couplers and shaft collars.  Hmm…