Filament Feed Tube - a Z-Artifact Fix?

In a previous post I went into detail trying to explain and cure the z-artifacts that I see in my RepRap's prints, though I had only been partially successful, I did mention that there were still more things to test and to try.

Well, a few days ago, a teflon (PTFE) tube arrived in the mail - a guide tube for my filament. Other than possibly being able to fix certain kinds of Z-artifacts caused by filament dragging and pulling the carriage around as the carriage is not 100% solid, the tube allows for peace of mind for unattended printing. This is because it transfers the drag of pulling filament off the spool directly and only to the extruder instead of pulling on the weaker X axis which can cause devastating skipped steps.

THE SET-UP:

The tube with filament in it. It is important to make sure that it will have adequate length to comfortably service the whole range of the machine's motion. Also, the tube does not have to be a tight fit to your filament's diameter, mine has an inner diameter about a millimetre larger than my filament. It is best to try and use a tube with as thin walls as possible to reduce the drag on the machine from having to bend the tube + filament.

Teflon cannot be hot-glued directly so I attached two tightly-fastened zip-ties to the tube and then glued the zip-ties down with plenty of hot glue. Using two zip-ties with a decent amount of spacing is important or the force of the tube being bent will put a lot of twisting force on the first tie and quickly pull it off. The tube only has to be fixed to one structural point; the extruder end of the tube is not fixed down.

THE RESULTS:

 

My first print with this modification on my printer. The layer alignment looks very good but that is mainly due to the shape of the object and lighting hiding still-present Z-artifacts

The layer alignment problems are easier to see at this angle with a different lighting angle.

The bunny on the left was printed with the tube and the one on the right was printed before both the filament tube modification and also before I replaced my Z couplings with super-flexible hosing tube.
You'd be hard-pressed to spot much difference - which indicates that the Z-artifacts weren't coming from the older Z leadscrew coupling or lack of filament feed tube.

WHERE TO GO FROM NOW:

I think I will build a new extruder cold end (the feeding mechanism) as I suspect that the hobbed bolt currently installed may not be perfectly even. Now having access to a lathe, it should be very easy to create a precise bolt. Also, I have noticed that the gears on my current extruder do not mesh evenly and have some problems with eccentricity. All of this could be leading to slightly irregular feed rates of the plastic - it only takes a small irregularity to cause significantly more or less plastic to be fed, which in turn is easily observable as layers having too much plastic and squeezing out. I will post an update when I get around to trying this.