Qu-bd is a low cost and decent extruder. However getting it to work is little challenging. This instructable aims to improve qu-bd extruder by spring loading the filament as suggested in forums. Most of the modifications used a small ball bearing pressing the filament against the drive gear. Since I had abundant supply of slightly larger bearings (608's to be exact) I decided to design a spring loading mechanism to utilize what I already had at hand.
I also changed the drive gear that came with the extruder with a makerbot MK7 drive gear as it provides a better grip. But not enough to solve the problem. The issue with the extruder is that the filament is pushed against the gear by means of a set screw on the side of the UHMW block. As things get to heat up and moving the screw gets loose and gear looses grip. Causing prints to fail midpoint.
I have searched the forums and found that people solved this issue by spring loading the filament. But most designs where made to use small ball bearing and I had bunch of larger bearing laying around.
I get to work at TechShop to design my own. I used the AutoDesk Inventor installed on techshop workstations and designed my pieces. Then used one of my favorite machines available at Techshop - a 3D printer - to print out my design.
This spring loaded version of the qu-bd extruder works a whole a lot better than what it used to. I managed to get print pieces without failure.