Metal z coupler question

Is the threaded rod supposed to be sitting on top of the motor shaft or is there speed to be a gap? I have a gap on mine but I can see the z axis changing from the coupler springing up and down.

Mine are set up without a gap.

Mine sit on the motor for the reason you mentioned.

I put a ball bearing (an airgun BB actually) between the motor shaft and the threaded rod.

Thanks for the input. I'll get mine changed.

I leave a small gap in mine. The weight of the X axis should be enough to compress the metal couplers enough to take out most bounce. If you have a bent Z rod, you want a small gap there to let the z rod and coupler flex so it doesn't affect the X axis as much. If the rod were in contact with the motor shaft, it may not flex as easily, and you'd get some artifacts in your prints.

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Originally Posted by AbuMaia

I leave a small gap in mine. The weight of the X axis should be enough to compress the metal couplers enough to take out most bounce. If you have a bent Z rod, you want a small gap there to let the z rod and coupler flex so it doesn't affect the X axis as much. If the rod were in contact with the motor shaft, it may not flex as easily, and you'd get some artifacts in your prints.

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Good point on the bent Z rod. I may try TJC's idea of the ball bearing

Ball bearing allows the rotational and torsional compliance with an out of true z threaded rod (they all are out a little) without introducing Z height concerns.