QU-BD Extruder Modifications

Remake of bdring's extruder mod. Thank you bdring!

This extruder block and lever is used with an mk7 style drive gear and McMaster-Carr pn 6138k64 bearing with 3/16 inch ID and 1/2 inch OD. This extruder mod does not require sourcing any screws, which is its main benefit. Simply push the bearing onto the printed shaft for a snug fit. The design is mounted with the mk7 style drive gear set screw positioned away from the stepper motor so that the set screw rests on the stepper spindle flat