<p>I have a cheap cartesian printer with the usual arrangement - X axis with three linear bearings, build plate moving as Y axis on three linear bearings as well, Z axis with lead screws. After about 2 kg of filament printed, I can see that one of the linear bearings (the single bearing on one side of the Y axis) is leaving an almost black residue at the front of the axis. I have thoroughly oiled all of the bearings before mounting them and repeated that after about 1 kg of filament printed. No other bearing is showing this issue, and the black goo appears only on the front side of the rod, not the back side. What might cause this goo - is the bearing breaking up or is it just some residue from the manufacturing process that is slowly being pushed out of the bearing?</p>

[{'answer_id': 3593, 'author': 'vwegert', 'author_id': 4620, 'author_profile': 'https://3dprinting.stackexchange.com/users/4620', 'pm_score': 1, 'selected': False, 'text': '<p>After completion of the print job, I was able to perform a closer inspection. The black goo contains metallic particles, and the rail the bearings are riding on has a visible groove - which means replacing both the bearings and the rail.</p>\n'}, {'answer_id': 3718, 'author': 'Alucard Pawpad', 'author_id': 6370, 'author_profile': 'https://3dprinting.stackexchange.com/users/6370', 'pm_score': 0, 'selected': False, 'text': "<p>Your new oil butted out the old graphite lubricant. </p>\n\n<p>Don't know about the metal particles though, might be dust, or your new oil caused damage to the bearings and/or rails.</p>\n"}]
['https://3dprinting.stackexchange.com/questions/3590', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/4620/']