For whatever reason, it seems to me like the concept of a reverse bowden tube isn’t very widely known, when it really should be standard for all printers with direct-drive extruders. So, with this post, hopefully we can start to change that. I personally stumbled upon the idea when it was offhandedly mentioned in a comment on thingiverse, and after adding a reverse bowden tube to my own printer, a whole host of problems related to irregular layer widths disappeared, which I had spent a month or more trying and failing to fix. I’ve seen a few others mention that adding a reverse bowden tube significantly improved their print quality after struggling with similar print defects, but the mod never seemed to get the appreciation it deserved.So, just what is a reverse bowden tube, you ask? Unlike a regular bowden tube, which guides the filament between the extruder and the hot-end in a bowden setup, a reverse bowden tube guides the filament between the extruder and the filament spool in a direct-drive setup. Similar to how a typical bowden tube forces the filament path to be a fixed distance between the hot-end and the extruder, a reverse bowden tube fixes the distance between the filament spool and the extruder. This prevents the filament from requiring varying amounts of force to unwind it from the spool as the extruder moves around on the printer. Without a reverse bowden tube, this variance in the necessary force to extrude a given amount of plastic shows up in prints as seemingly random (and potentially quite ugly) layer variations. Since the force required to unwind the spool is different even between two consecutive prints made from identical g-code, troubleshooting the error can be incredibly frustrating, since the defects are different for each one.Adding a reverse bowden tube to your printer is very straightforward. First, feed your filament through a bowden tube before it hits the extruder. Secondly, and this is important, make sure to constrain the end of the tube closest to the filament spool so that it can’t move. Seriously, make sure to do this – without fixing the far end in place, a reverse bowden tube won’t actually do anything. Fixing one end of the tube in place ensures that the filament path always has a constant distance between the filament spool and the extruder. This way, the amount of force required to unwind the spool is constant, regardless of where your extruder is, and your irregular layer lines will be vanquished at last!tl;dr – have a direct-drive extruder and suffering from irregular extrusion? put a bowden tube between your filament spool and extruder, and fix the far end of the tube in place so it can’t move. Boom, problem solved!Sources and examples:Taxonomy of z-axis artifacts – a classic guide to dealing with z artifacts. A reverse bowden tube is briefly mentioned towards the end.reprap bowden tube on cold end – a brief video illustrating one possible setuphow the TAZ 6 uses a reverse bowden tubePS – please please please, let’s not turn this into a flamewar debate about bowden vs direct drive set-ups. The pros and cons of each setup have been established long ago, and don’t need to be rehashed here. This post was meant merely to help those who already have direct-drive extruders improve their print quality with a quick-n-easy (and cheap!) upgrade. http://ift.tt/2aRoFld