QU-BD MBE Spring Tension Arm

thingiverse

Tension Arm with 608 Bearing: This arm is designed for the QU-BD MBE Extruder and operates using a common 608 bearing, often found in skates and roller blades. Despite its low cost due to slow operation, an inexpensive bearing suffices. It works with the standard raptor gear via the groove, although a tight clearance is experienced initially; once loaded with filament, it runs smoothly. The arm's strength exceeds other designs, especially when printed using PLA, preventing warping from extruder and bed heat. Design inspiration stems from Barton Dring's spring tensioner (http://www.thingiverse.com/thing:38281). Note that an MK7 gear is recommended for use. The provided screw strengthens the arm laterally but not bearing placement, as it remains secure between the arm and heatsink. If no heat sink exists, a button head bolt and washer suffice. Drilling may be necessary to ensure smooth pivoting. For opposite-side mounting, adjust printer settings' scale accordingly using Repetier Host without locking scales. A raptor gear initially works but MK7 performs better with this arm. The original arm printed at 400 microns exhibited no warping or deformation after extended use, and increased PLA settings provide additional assurance (200 microns, 80% infill). Concentric top fill pattern is utilized.