Product Description
Problem:
We received an APO (refractor) telescope for repair, and the customer reported that the focuser was no longer working properly.
During on-site testing, the focuser made a scraping noise and could no longer be screwed in or out smoothly. Upon closer inspection, it was also noticeable that the focuser was very stiff when turning, tilted, and repeatedly jammed.

Solution:
Gummy Ball Bearing
The threaded attachment that moves the focuser was unscrewed. It quickly became apparent that the grease in the ball bearing was very gummed up. This explained the stiffness.
The ball bearing was thoroughly cleaned of old grease and regreased.
Tip: Make sure there is no grease outside the bearing; you don't want it on the lens. Always maintain cleanliness and be sure to wash your hands after each step!
Although the thread now ran smoothly and without blockages again, the tilting and scraping noise were still clearly felt and heard.

Broken plain bearing
After removing the entire focuser/attachment, a closer inspection of the rearmost plain bearing revealed a cracked ring with a tilted ball inside.

The only solution was to completely replace the affected plain bearing. With a bit of fiddling, the locking screw was loosened and a new plain bearing inserted.

Once everything has been replaced and reinstalled, the interaction with the grub screws and locking screws needs to be tested and optimized.

After a functional test, the focuser ran smoothly, easily, and without any noise.

Before: