I tried an expanding mandrel type before choosing to make the other angled-cut type. The expanding mandrel was a tapered plug at the end of a section of all-thread which was pulled into the split mandrel, but it didn't hold very well, and was fiddly to release, so I made the other, angled-cut type.
The angled-cut type works well with only a moderate amount of torque to secure it, and the cut line isn't placed at the location of a bearing, but farther inside the spindle. I would expect the grip to be spread out over much of the entire length of the "fastener".. but possibly not.
When I locate a good heavy duty motor (probably PM DC) for the 9x20 lathe, I'll convert it as I did the other machine, and the hand crank will likely be reused for something else.
-- WB .........
That type of fitting presses the spindle tube oval, not good at a bearing.
I'd consider two concentric tubes, the inner one having a taper on the end that wedges the slit outer one evenly tight against the spindle ID somewhere far from bearings. It would work like a ball hole gage, but have an over-center cam instead of a slow-acting screw to operate it. The tapered cone could be a separate piece that screws on, giving an easy tension adjustment.
jsw