Printrbot Simple extruder fan mount

My Printrbot Simple occasionally has a problem with the extruder overheating during long prints. Other people also report having this problem, and have mounted fans to keep the extruder cool. This is my design for a 40mm fan mount, which works quite well.

I followed the [suggestion by Nathaniel Chapman](http://help.printrbot.com/Answers/View/8873/Where+to+plug+in+an+additional+cooling+fan+on+the+Printrboard) to power the fan from the heated bed port (which is unused); this requires putting a