[Lil' Lavery]

Can you explain a little more about what is going on with that top shaft? Why do you have it passing through three bearings? I feel like that is inviting the potential for both misalignment and over constraint. The shaft is short enough that hopefully it wouldn't be a real detriment, but it's also not very useful.

It's hard to see, but does the bottom shaft also have the same issue?

Finally, you may want to consider countersinking those exterior bolt heads in order to allow you to place your wheel slightly closer to your drive rail.