We ran into a little issue with one of our vertical mills and I was wondering if you could help me out. The machine we had a problem with is a Bulova BT400S. There is a cap screw on the side of the Z axis spindle column that worked its was loose, and when the Z axis rapids up to change a tool the head of the cap screw would hit a cover and make a loud noise. We just tightened the cap screw, and after we tightened the cap screw the spindle makes a whining noise when it rotates. So we loosened up the cap screw and made it just a little more than hand tight to keep the spindle from making noise. I guess my question is what does that cap screw do? I looked it up in the book, but the book doesn’t explain what it does. Should this screw be more than just hand tight? I would think that it is going to loosen up over time and back itself out again.

Edit: After machining for a day the screw worked itself loose again. Reaching out to service guys but it seems Bulova Machinery no longer exists. The documentation we have for this machine isn't good.

Photos: https://imgur.com/a/0qiqSTV