Bunny Science MK3S Geared Extruder Upgrade

thingiverse

Human: A simple, straightforward upgrade for the stock Prusa MK3S extruder is available in the form of a geared extruder mod. This modification enhances extruder uniformity by utilizing gearing similar to that found in Bondtech BMG or Skelestruder. Rather than replacing the entire extruder, this upgrade focuses on upgrading just the motor plate and idler with geared Bunny Science versions. The remainder of the stock R4 MK3S extruder remains intact and can even be left installed on the printer during the upgrade. It is essential to note that this motor plate cannot be used with the Bunny and Butterworth (BNBTR) extruder bodies. This upgrade specifically targets the stock Prusa R4 extruder body, ensuring compatibility without altering the filament path or air gap. Indexing pins on the BNBTR extruder body serve as a safeguard against accidentally installing this motor plate on an incorrect extruder body. Advantages of the Bunny Sciense MK3S Extruder Gearing Upgrade This upgrade offers several benefits: 1. Improves extruder uniformity via gearing, much like that found in Bunny and Bear, Skelestruder, or BMG extruders. 2. Reduces extruder mass by approximately 70 gm compared to the stock motor. 3. Minimizes moment arm by moving the motor closer to the x-axis than the stock motor. Upgrade Overview This upgrade replaces just the motor plate and idler door, leaving the rest of your MK3S extruder installed. The motor plate/gearbox must be printed with supports. A 3mf file is provided with suggested plating and support enforcement block specifications. Supports should only be specified for the gearbox portion up to the second bearing. Removing support material from within the gearbox cavity takes around 10-15 minutes. It's crucial to completely clean out mounting holes for bearings. The shaft rod can be pushed into the gearbox from outside to remove support material within bearing mounts. If you fail to clear out bearing mount holes entirely, bearings will not spin freely. Some support scarring may remain but is largely hidden by the installed extruder cover. Assembly Requirements Build with two shaft bearings; there isn't a third bearing for this upgrade. Required Materials: 1. 5 mm diameter shaft rod - Length: 61 mm 2. Pulley flat - 0 to 9 mm 3. Bondtech flat - 50 mm to end (see https://www.thingiverse.com/thing:3595205 for shaft cutting guide and instructions) 4. 2 x 1050ZZ bearings 5. 1 x continuous loop 140-2GT-6 Timing Belt 6. 3 x M3 square nuts 7. 3 x M3 set screws (3 to 4 mm length) 8. M3 hex nuts & bolts (various lengths from 12 to 30 mm long; some must be ground to custom length during assembly) 9. M3 washers 10. 1 x 16T drive pulley (to simplify alignment, use one for a 10 mm wide GT2 belt despite the belt being 6 mm wide) Motor Requirements The motor used in this upgrade is a 1.8 degree STEPPERONLINE Nema 17 Bipolar Stepper Motor with a rating of 0.7A and 13Ncm (18.4oz.in) torque. Wiring Harness You must also set e-steps by sending g-codes to your printer: M92 E980 M500 Pulley Gearing The pulley gearing in this upgrade was originally inspired by Skelestruder. Extended Flats on Shaft Extended flats have been added to the ends of the shaft for easier alignment during assembly.