Ender 3 Filament Roller Guide

Minor Update 02/10/18:
Bracket trimmed a little for more clearance to Z stepper motor, most sharp edges chamfered.

Getting the filament smoothly into your extruder feeder is rather important. With the Ender 3 the spool holder is normally mounted on top, creating a steep angle of entry, and if left unchecked will wear a slot in the feeder arm. The filament also rubs on the lead screw at the bottom.
There are a number of solutions to the above already available - this is just my take on it.

Also fits CR-10 (without filament runout sensor).

I like to design things that don't need extra hardware but to do this properly you will need a skateboard bearing and a 4mm bolt. Printed bearings or changes that create friction/slop are not an option.

The roller guide is a secure push fit onto the Z-axis carriage and requires no hardware to mount. It wont fall off, the filament is captive so it can't pop out of the roller or jam up. and importantly, it gives the filament a good smooth