Stepper Motor Shaft Failure

Kondia FV-1 turret mill, running Gmoccapy 2.9.4.

Y-axis Nema 34 sheared the shaft at the step where the diameter had been reduced from 14 mm to 1/2" (and grubscrew).
Unknown if done by previous owner or factory option.
Drive uses an unsupported pulley with T10 x 25 mm timing belt and significant tension.

Can anyone confirm that this is a recognized risk with this arrangement ?
With a reduced shaft ?

Both Y-axis and X-axis steppers replaced with new ones, with keyed 14 mm shaft.
John.

electrosteam wrote:

Can anyone confirm that this is a recognized risk with this arrangement ?
With a reduced shaft ?

I can not confirm, but i read a lot of Creality CR-30 3D printers have a failed motor shaft from factory, not reduced but long, and i do have a CR-30 that is still OK. The belt on those is 10mm wide and tight like a drum, literally.
The reason might also be the reduction on a lathe can leave grooves that might initiate the break due to tension and vibrations, so it seem plausible.
Best way to avoid this would be, granted the shaft is long enough, to make a bearing holder at the end of the shaft.

If the inside radius of the step is too small, that produces a weak point in the shaft. Frequently, when a shaft has to be reduced, tapering or rounding the step in the shaft largely prevents that weak point.

Think of the sharp inside corner of the step as being the starting point of a fracture beginning to form. That is where it will break.