About this 3D model
This is a modified version of the base of the Printrbot Direct-Drive extruder (http://www.thingiverse.com/thing:281015). I've altered it to be more easily printable, and to reduce the gap between the drive gear and the base to make it more ninjaflex friendly. *Update 7/23/2014*: I've tested this with PLA, ABS, and MatterHackers Soft PLA. It works great for all of them. I don't have any genuine NinjaFlex, so if you try it, let me know. *Update 7/23/2014*: Minor updates to improve fit.