You're not implying that the axis is using the stepper motor bearings as a mount for the leadscrew, are you? That would be a serious design flaw. Stepper motor bearings are only there to hold its shaft central in the windings, and usually have endfloat built in to protect against binding as the motor heats up in operation and thermally expands. The leadscrew must be separately supported, both radially and axially. The motor is only there to turn the leadscrew.
Randy