Quote Originally Posted by Swarfing View Post
No it is a taper bearing at the bottom
Ok that makes sense, deep groove bearings pre-loading a taper which can take axial and radial load. I would have thought an AC at the top would have been better as you still get the speed increase from using ball bearings but not the heat issues with pre-loading deep groove bearings, (as you are forcing them to run on the edge of the race) excessive heat will cause expansion and reduce the pre-load on the bearings and therefore rigidity.

This is the theory so it will be interesting to see if in a hobby environment it is actually a problem. that is what I'm trying to find is the balance between the ideal design and what works in practice.