I just got a freshly built K8200 / 3Drag Reprap for fine tuning.
Never in my life did I need so many tools for one device.
The construction uses has some nice details (especially the extruded aluminium frame), but some parts are worryingly cheap.
Compared to my Ultimaker (which is all better than my CTC Makerbot clone) it’s more inaccurate (0.5mm nozzle), and (surprising for me) also very quiet at speeds the Ultimaker wouldn’t like.
It has some odd things, and maybe owners of similar printers can help me:
The z-axis hase some problems:
The threaded-z rod is slightly excentric and produces a lot of friction despite lubing.
And worse: the z-double bearings seem to get partly stuck somehere on the lowest milimeters. Has anybody else experienced this?
Also, is it normal for the extruder gear to produce so much dust? It literally rains on the print, look at the pictures! 
Thanks!
PS: Do you have any recommendations for must have upgrades to a 3Drag/K8200?
Well, at least you have nice, smooth interfacing surfaces on the gears now…
There’s probably too much tension on the gears, I’d loosen them up a bit. Also, unless some of that dust is a dry lubricant that was put there intensionally, you could probably use some lubrication. My instinct would be to go with a grease lubricant, either lithium or silicone, but I don’t really use plastic gears, so somebody else might have a better idea.
Have you lubricated your extruder gears? Other than that all I can think of is that they still need some wearing in.
Dust in gears - ouch. Do you have a way of moving the gears apart a bit? This could ease the pressure that grinds them. If you can, ease the fastening of the motor/small gear and have it rotate freely some humdreds of mms in both directions - observe any uneven behavior that could mean you got an oval gear 
Dunno if it’s possible on gears of industrial make. Otherwise, there is a chance they will rub between themselves until their contact is good enough, but more likely they will fall apart first - better print some spare ones out of PLA
These K8200 have appeared in shops in Russia as well, of all places, and ever since I have been wonderin just how good their quality is. How’s the joint between vertical and horizontal frame parts? it looked awfully small, but that my be because the frame itself is largish.
As for the rods - try replacing? They should be dirt cheap.
Z bearings being stuck - do they do the same when you move them by hand? Maybe it’s another problem with the rods.
I use beeswax for stuff like this. It’s kinda seems low-tech but it works and isn’t messy.
2nd the beeswax on plastic gears. I’ve used 3 in 1 oil as well, which works but doesn’t last very long.
2nd the lithium grease for everything. As opposed to beeswax (or WD40-stlye oils) it’s a proper lubricant and also sticky enough to hold on to any worn-off particles.
I have no beeswax, so I used some ElectroLube (it’s a ‘plastic lubricant’ grease). No more dust (or at least it gets absorbed by the grease). Also lubing the z-spindle seems to have yielded success (after a while). The Magnalube in threads looks real dirty, but movement is much smoother now. The bearings also dont seem to get stuck any more (for whatever reason).
I’ve used grinding paste and a tungsten carbide blade to remove the worst burrs from the z-spindle (at least at the lowest few centimeters). After cleansing and heavy lubing I also fixated the hex nut slightly with cardboard.
Prints looks slightly better now.
X-Y accuracy is still only ±0.15mm (after tensioning the belts). I guess it has to do with the fact that the belts run over a plain ball bearing (instead of a pulley) on one side.
