what does this do?

[RobSm]

Hi - I spotted this nut spinning on the lead screw Y axis. I tightened as best I could so it now rotates with the lead screw. Top right photo.

What does it do and should I just tighten it to very tight?

I would have to decouple and remove the Y stepper to do more.

Thanks,
Rob,

[Jim Dawson]

Looks like it adjusts the end play on the support bearing.

[CitizenOfDreams]

This nut adjusts the bearing preload. There is a pair of angular contact bearings there, the nut squeezes them together to eliminate the backlash.

The nut should be tight enough to remove the backlash yet loose enough to let the bearings rotate freely. Once adjusted, the nut is secured in place with a set screw (which has probably been lost on your machine).

[RobSm]

Thanks guys.

[RobSm]

Thanks again - can you suggest a safe way for me to re-tighten this nut.? Assuming the set screw is around somewhere (or I source a replacement) I'm pretty much limited to screwing the nut forwards or backwards along the lead screw into the housing.
Is there some reasonably simple way of divining the correct position?

Regards,
Rob.

[joeavaerage]

Hi,
the highest quality angular contact bearings come as matched pairs. The faces of the ball races are ground such that when the faces are held
tightly in contact with each other there is perfect preload between the bearings.

A matched pair of P4 (high grade) 7204's say could cost $200 plus a pair whereas just plain 7204 bearings can be had for $10-$15 each.
What grade of bearings do you suppose are fitted to your ballscrew? If its a cheap Chinese machine then you might reasonably guess just plain unmatched
bearings. That being the case just do the nut up finger tight or a bit more then lock it so it cannot undo.

If high quality matched bearings then you can tighten the nut to your hearts content, the faces of the bearing races will abut each other and further nut torque will
not result in increased bearing pre-load.

Craig