I was reading an article about z banding (I made another thread here about it) and came across another possible suspect. One I had never considered; pulling the filament from the spool could have enough friction to lift the extruder by tiny amounts causing the print to have occasional bands.It also suggests using a guide tube to fix that. But I don’t know how that helps, as it only adds more friction. Also, a lot of people/printer use these guide tubes. Why? Everyone seems to think they need one but I couldn’t find any explanation of why. http://ift.tt/22YiQXo