Ball-screw spline revealed

The blade-bearing cutting head on the case cutter is affixed to the bottom of the shaft (A) in these cutaway drawings of the ball-screw spline.

Pw 5438 Thk 1outline
The outer rings on both the ball-screw nut and the spline nut remain stationary.When the ball-screw nut pulley (B), which is attached to a servo motor, spins the ball-screw nut, its ball bearings engage in the grooves of the shaft and cause the shaft—along with the cutting head affixed to the shaft—to move up and down. While the ball-screw nut causes the shaft to stroke up and down in a vertical axis, the spline nut helps guide that movement and keep it true.
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