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Black belt debris in UM2?

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After getting my nozzle cleared of the black carbonized PLA that quickly builds up if you ever let PLA sit without extruding at temps over 190C, I still found tiny black flecks of something occurring randomly in my prints - particularly annoying since I've been printing a huge project in Ivory PLA.

I finally pinned it down to rubber debris wearing off the belts, and then getting blown around by the fans and landing in the print.

I noticed that the top of both motors at the rear of the UM2 were becoming covered in black particles of almost dust-sized stuff, and concluded that it had to be rubber from the belts wearing. After a thorough cleaning of the motor area and the rest of the build area, no more black dots in my printing.

Has anyone else noticed this stuff, or are my belts too tight, or skewed and misaligned or something?


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I had that problem on my UM original for a while when the belts were rubbing against the wood side on one spot but never on the UM2. It didn't look like the belt was rubbing but it would twist slightly every time it changed direction - that was the give-away.


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I have the same issue at the front. But I guess there is not much that one can do, isn't it? The pulleys on the UM2 fix the rods and thus they should not be moved. However I could imagine to print the black spacers in a slightly different size in order to relocate the pulleys...but actually I'm not very keen of taking my UM2 apart...

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