creates an axis for a 606 bearing to roll using an M3x16 screw.
I didn't find any M6x16 screws to use in http://www.thingiverse.com/thing:7113 so I created an adapter to use one of the many M3x16 I had around.
this way the plastic can bend a little to the inside to create a litle pressure between the bearing and the screw
-USE A RAFT
this will prevent the tube from falling whith the movement
-USE THE MULTIPLY PLUGIN
I went for 3x3 but you can probably use 2x2.
I had to because the plastic was melting a little too much and I was getting warped pieces.
you probably can use the cool plugin, but I didn't try