[jdixon9999]

There is a bearing shaped part between the coupling and the large OD threaded mount that the stepper motor mount screws onto (see the attached image). It spins with the ball screw but can be stopped with finger pressure. What is it? Could it be used to prevent the Z carriage from dropping when powered off?

[awerby]

That looks like the bearing that supports the ball screw. It seems to have moved towards the motor - it should be further back, inside the housing.

Is that the Z axis, or another one? The headstock shouldn't be dropping when powered off. Are you using the stock motor, or something heavier?

[jdixon9999]

Thanks for the reply.
Stock motor, upgraded to ball screws.
The ball screw bearing is secure in it's housing.
This part is just inboard from the coupling, and is in the same position in all 3 axes (this machine is ~10 years old, so newer versions might be different).
From the feel it is some sort of slip disc mechanism, which seems to have the correct amount of 'drag' to keep the z axis from back-driving the ball screw. But I don't want to use it that way until I know what it actually is.

[sclelectronics]

On the old ACME screws, it is the Increment Dial spacer.. On the ballscrews they are not index marked anymore... Just spacer block.....