Ender 3 Filament Roller Guide at Top

Minor Update 20/3/19:

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