Geeetech

Call it Z-banding or Z-Axis wobble, it's something that can easily be reduced. The contributors to the effect is mis-alignment of the drive nut on the two Z-Axis with the Z-Axis motors. These two planes have to be in perfect alignment, something that can't be expected on a $200 printer! The contributors to the error are many;
1. Not 'true' threaded drive shaft
2. Couplers that don't run true.
3. Mounting hardware not in perfect alighment.

Number 3 can for the most part be ignored, most of the Acrylic and Aluminum frames are laser cut and quite accurate.
Number 2 is a problem, on my printer one unit was perfect the other was a wobbly gobblin
Number 1 can be a problem but like checking the roundness of a drum stick, just roll the rod on a flat surface and you can verify if they are out of round (mine were perfect).

I didn't think the coupler would be a problem since the design is to isolate these imperfections, but what I found was far from isolation. My prints were fine but then I reviewed this mod on thingiverse:
http://www.thingiverse.com/thing:1782670
I was skeptical, but printed these and installed on my printer. The results are great. A big improvement over stock configuration. I hope to post my findings onto youtube so you can really see the amount of wobble this minor mod isolates.

Thank you for your experience sharing.

Thanks for the links etc..

i have had issues with z banding.. and i think in the early stages anyone thats new to 3d printing will come across it. i have seen lots of videos and posts on thingiverse but i have yet to see a proper before and after video / picture. The ones i have seen reduced it, but did not fix it. My fix would be.. make sure your threaded rods are straight. my set were, but i ordered a new set anyway. The geeetech smooth rods are not very good, one was loose in the bearing, the other too tight. which failed after a couple of prints. so would suggest new smooth rods. ( a problem which will still arise even with the z wobble fix ). Poor belt tensioner bearings / pullys, replace these with good a toothed variety. Then many people do not understand how to install a coupling correctly. yes the supplied ones are not the best. but install them correctly and they work just fine.

I have seen some amazing prints come from this machine without all the mods and addons. yes a nozzle cooler is recommended. but other than that if built correctly you will not need the rest.