Black on the z-axis threaded rod  

RE: Black on the z-axis threaded rod

This is probably grease.  How old is the printer?  Did you assemble it yourself?  

RE: Black on the z-axis threaded rod

@virtech

I'm not sure if it's some kind of Oxidization, or if it's dust and dirt from the environment trapped in grease, but I have that same build up of black in the areas that the Trapezoid nut axis travels in, and I think the grease attracts a certain amount of dirt and holds it, however it does not appear in the areas below the range of travel, (they are still shiny). I believe the threaded rods are nickle coated so they should be fairly resistant to Oxidization. on my oldest machine they are black even though I do regular maintenance, 5 years and several 10's of thousands of hours in and no problems that I can associate with this to date.

I use a paper towel and a mild degreaser on them to clean before greasing again during maintenance. 

Just my thoughts and observations, I've wondered this myself. I own three Machines in the MK3 series.

Regards

Swiss_Cheese

RE: Black on the z-axis threaded rod

That makes sense.  I clean my threaded rods once a month and do not have this.  

RE: Black on the z-axis threaded rod

I think black are remains of friction between trapezoidal nut and rod. I would guess, that friction increases if trapezoidal nut is tightened fully with those two bolts (trapezoidal nut should have a little "free play").

RE: Black on the z-axis threaded rod

This was my thought too, didn't know if I needed to have a spare set of the trapezoidal nuts on hand in the event it wears too much.  As other have mentioned I'll just start cleaning the threaded rods from now on.

Thanks all for sharing your knowledge =D