The Z axis motors have their load weighing down directly into the shaft. Am I right in thinking that's an excellent - but unconventional - arrangement? Doubtless it's not a problem for us but, out of interest, how much load can a stepper take like that? I tried looking at various specs but couldn't find anything.....
You would have to look at the bearing specs. I think the steppers used in the BB have 625Z bearings. They have a static radial load rating of approx. 380N. And axial load rating is approx. 20-25% of radial rating. So 2x380x0.2 = 152N Ref: http://www.smbbearings.com/technical/bearing-load-rating.html
