I guess I probably tightened the bearing clamp screws a bit too hard when I initially assembled the unit. This “sometimes” caused interference on the X-axis movement in the positions where the rear X-axis bearing clamp passed by the two large openings in the rear panel, since the bearing clamp screws protuded just a little bit too far through the nuts.
Strangly, the problem was not consistent! - I therefore assume that it mainly depended on the ambient temperature. When my workshop was cold, nothing abnormal happened. But after some hours, when both the room and the printer got slightly warmer, those screw ends would clearly start to “hook on” to the edges of the rear panel openings. They have also left a small but visible scratch trail on the rear panel, running along the width of X-axis movement.
I finally verified that there was basically NO clearance whatsoever between the screw ends and the rear panel of my printer when it was cold. Not even a single sheet of paper would pass between!
For all people out there who like to tighten down things in a vibrating environment real hard (like me), I have two hints on how to avoid this issue:
[ul]Alt. #1: Find small suitable washers that will fit underneath the screw heads.
Alt. #2: Shorten the four (4) affected screws by approx. half a millimeter.
[/ul]
I removed the screws and used my Dremel to grind them down a bit, as per alternative #2 above. I also had the nuts threaded on to the screws when I did it, to make sure that any possible distortion to the threads would easily be cured by simply unscrewing the nut afterwards. Now I finally have a clearance between the screw ends and the rear panel. A good old-fasioned “punch card” (anyone in here who still remembers them?) will now easily pass between. Luckily, the removal and re-insertion of those four screws proved very easy, since the nuts can be freely accessed via the rear panel openings when the carriage is in a suitable position. It would definitely have been a lot worse if the same problem had manifested itself on the front side, but there I actually have a 0.2 mm clearance.
Just a small quick-fix tip to you folks, for whatever it might be worth. I guess someone somewhere out there might one day experince the same problem…