Summary

This is a modified version of Blackice83's guide. The slot that allows for sliding the filament in and out has been altered to an S shape to prevent the filament jumping out during printing.

Instructions

I tried this guide and it works great. When i was drawing it, my goal was to make the spool feed to the extruder as fluid and smooth as possible with the least amount of force needed to pull in filament. So with this design i noted, when the extruder head goes far left or right along the X axis, it does put a small amount of tension on the filament because this guide is typically positioned in the middle. To resolve that I build a wide mount variation that comes in 3 parts witha dove tail fit connection. It works like a charm http://www.thingiverse.com/thing:62386

Filament Guide v4 - revised S slot