Weld the square stock onto the axle

[zenmanenergy]

Remove the notch for the square stock on the axle. Just increase the size of the square hole in the disks so the square stock can sit on the tangent of the axle. Weld it into place.

This requires one fewer operations.

[zenmanenergy]

In the 138mm version I switched to a 14mm threaded rod for the axle. I used a lathe to turn the ends of the axle down to a dimension that fits inside of the ball bearings.