Next on my agenda was to upgrade the X-Axis bearings from LM8UU to the same Self-Aligning, Self-Lubricating Sintered Bronze Bearings that I used in the Y-Axis. After printing out a bunch of X carriages, I decided I didn't like any of the designs for various reasons, not even the ones I designed myself, so I decided to modify the existing carriage. Please note that is you do this, you cannot go back to the LM8UU as the bearing outside diameters are different (15 mm vs. 15.9 mm). After disassembly of the X-Axis Carriage this is where things get interesting. Took my carriage to the drill press, but any drill can work with some care. Chucked up a high speed steel (it's what I had) 5/8" drill bit. A 5/8" drill bit is 15.82 mm so it is close enough to get a snug fit on the bearings. Drilled out the two holes that hold the LM8UU bearings. Then used a few Q-Tips soaked in acetone to smooth out the surface of the the holes on the inside and to gain the few hundredths of a mm I needed. The new bearings then just press in. Used the same technique to "pre break-in" the bearings once installed (outlined and video link in Y-Axis Upgrade thread). Had to use the same Q-Tip / acetone trick on the left X-Axis Idler Arm as there was a small discrepancy in the width of the two X-Axis rails (measured exactly 83 mm c-to-c on the right, but 82.7 mm c-to-c on the left) which caused the X-Carriage to bind near the X-Axis home position. Reassembled. Here is a video after installation. It demonstrates how much less noise there is with these bearings over LM8UU's. The first few seconds are with no movement so you can get a base reading on just how noisy the fans are. The video shows a Auto Home sequence (need to tune the speed and retune the stepper drivers since the bearings are a bit snugger) there is a very slight shudder which will smooth out as the bearings are broken in. Following this was an Auto Bed Level Sequence. Y Axis bearing replacement thread located here.