PR model Z axis bearings

[waynec]

I just cut my first 3D file, and I'm delighted, except..

The Z axis is not holding its height. I've got several variance in the range of 1/16 to 1/32 of an inch in Z over the course of the two hour cut. It drops, then goes back up, then drops again on what should be a flat surface.

During the cut I listened to the Z movements, and I think I hear the top bearing on the ball screw making noises. The lower one seems OK.

How do I check this bearing to see if its the problem? If its bad, how do I do the R&R and get things put back together accurately?

Also, my Z axis stepper motor is just tywrapped to the frame at the top. The bolted-on bearing holds the ball screw, and the motor rides the top but is not bolted in place like I'd expect. What is normal for mounting the motor on the PR Z axis?

Thanks for the help!

[ron brown]

Wayne,

Your setup sounds like a typical old ball-screw "Z". The accuracy is handled by the uni-strut rails and the rollers.

First make sure everything is tight. Be sure and check the bearing mount. There are (if I remember correctly) "grub screws" into the ball screw that might work loose. Be sure and clean the roller bearings that ride on the strut.

Removing and cleaning the ball-screw can be interesting, to say the least. Be very careful there.

Everything seems to be prety straight forward on "Remove and Replace". Start at the top, cut the "ties" the motor and spider remove. From there, you may be able to find what is causing your problems. If not, just keep diving deeper.

Good Luck,
Ron

[waynec]

Thanks Ron. I'm gonna do a cleaning pass, then do another quick 3D test. If that still has variance, I'll start a process of remove and replace. I suspect the top bearing, so I'll start there. Gotta learn it sometime. Now sounds good.

Thanks for taking the time to respond.

Wayne

[ron brown]

I'd suspect something loose.

Ron