While converting my Printrbot Plus to use Bowden tubes (dual extruders look out!), I decided that I wanted the extruder to sit at the top of the Z-Axis shaft rather than stand alone. It is paired with my Ubis Hot End Bowden Mount.
The Bowden tube gets pretty bent when the X- axis is homed and at the top of the Z-travel. It still works, but the additional friction doesn't help the ooze. Next design will put the extruder centered (and higher) on a cross bar linking the Z shafts.
This model is for the Printrbot Plus 12mm Z shaft, the OpenSCAD file has a parameter line: __printr_shaft = 6; // plus = 6, lc = 4__ . This is the shaft radius. Change it to 4 for the 8mm LC shafts.
I made this with measurements from the Printrbot and pneufit adapter: SPC-06-01 Pneumatic Push to Connect Fitting. This fitting uses a British Standard Pipe Taper Thread R1/8". Tap size is 8.4mm for this thread, but I'm 'self' tapping with the thread itself into the plastic. I'm using 9.45mm for the base and 9.15 for the tip (it tapers.) I bought these from eBay
I printed this (using a Bowden setup!) at .8 infill.