Bunny and Bear Geared MK3 Extruder

Note: This project has been superceded by our more advanced "Short Ears" extruders that feature even shorter moment arm, separately printable hot fins, Mosquito capability, and better filament sensor systems (on the MK3S)

For MK3 https://www.thingiverse.com/thing:3606189

For MK3S https://www.thingiverse.com/thing:3626993

Their Mosquito kit https://www.thingiverse.com/thing:3651160

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Integration of the Bunny Science Gearbox with the Bear Extruder

There are three, interchangeable motor plate options for the Bunny and Bear Extruder.

1. Direct drive - allows direct use of NEMA 17 motors and places motor 2 mm further towards x-axis than standard Bear.

2. Geared drive - improves extruder uniformity via 1:3.5 gear ratio

3. Retrograde, geared drive - geared and reduces moment arm by moving short body motor 14 mm closer to x-axis.

My recommended option of these three is the retrograde, geared.
Better yet, the BNB "Short Ears" extruder https://www.thingiverse.com/thing:3606189 further improves motor positioning, but requires changing motor x-end.

BNB extruder yields these advantages....

• Improve extruder uniformity via gearing like Skelestruder or BMG extruders.

• Reduce extruder mass by about 80 gm, if short body motor is used instead of stock motor.

• Move motor 4 mm closer to x-axis than possible with just the Bunny Science Gearbox. Reduces moment arm of moving motor farther from axis.

• If retrograde motor plate is used, motor is 18 mm closer to x-axis.

• Straight-in hot end insertion like MK3S extruder. No more "special angle technique" needed.

• Use with https://www.thingiverse.com/thing:3610593 BNB universal x-carriage for easy motor plate removal without tearing down extruder.

• Convenient PTFE tube replacement with removal of just motor plate without extruder tear down.

• Accessory motor plate conveniently reverts extruder back to ungeared, direct drive.

If you do not already have a standard Bear extruder and X-axis, you will also need to print some pieces from the original Bear extruder and axis (https://www.thingiverse.com/thing:3226689)

extruder cover
filament_sensor_cover
hotend_collet_clip
x_end_idler_idler_mount
x_end_idler
x_end_motor
PINDA clamp (now included here)

Use our universal x-carriage to mount this extruder on either Bear or Prusa x-axis. The universal carriage has easy motor service features.

See Bunny and Bear Universal Carriage https://www.thingiverse.com/thing:3610593 for more details about the universal carriage.

Although the BNB universal carriage supports use on a Prusa x-axis, I strongly recommend the Bear axis with a BNB "Short Ears" motor x-end. The Bear axis gives you dramatically easier belt insertion and tensioning. The Short Ears x-end prepares you for the more advanced "Short Ears" version of this extruder.

Motor plate / gearbox MUST be printed with supports. 3mf files are supplied with suggested plating and support enforcement block. Prints better with front face down on plate. Specify support only for the gearbox portion and up to the 2nd bearing. This leaves filament path unmarred by support material. 3mf's are set for 0.15 mm layers for nicer finish.

Removing support material from inside gearbox cavity takes 10 to 15 minutes. Take care to completely clean out mounting holes for bearings. Push shaft rod into gearbox from outside to remove support material within bearing mounts. If you do not clear out bearing mount holes completely, bearings will not spin freely.

Some support scarring will remain, but is largely hidden by installed motor.

Build with THREE shaft bearings. 3rd bearing goes in rear of extruder body and fully supports shaft.

see https://www.thingiverse.com/thing:3595205 for shaft cutting guides and instructions

Materials needed...

1 x 5 mm shaft rod shaft. Prep with below lengths and grind two flats 0.38 to 0.4 mm deep
Bunny and Bear Retrograde
Length 58.5 mm for 2 bearings (Optional 62.5 mm long if 3 bearings)
Pulley Flat 0 to 9 mm
Bondtech Flat 48 mm to end

Bunny and Bear Antegrade
Length 44 mm (3 bearings)
Pulley Flat 0 to 15 mm
Bondtech Flat 26 mm to end

3 x 1050ZZ bearings
1 x continuous loop 140-2GT-6 Timing Belt
1 x M3 square nut
1 x M3 set screw
M3 hex nuts & bolts (various lengths from 12 to 30 mm long. Some must be cut to custom length during assembly)

M3 washers
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 - 1.8 degree, STEPPERONLINE Nema 17 Bipolar Stepper Motor 0.7A 13Ncm (18.4oz.in) 17HS10-0704S. This is the ONLY short body motor that worked well in my testing.

Wiring harness for motor.

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You MUST also set e-steps by sending g-codes to printer
M92 E980
M500

Retrograde Geared Option
https://youtu.be/RBTR8ucOMfA

Standard Geared Option
https://youtu.be/4aEE6gMUx9s

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Pulley gearing inspired by Skelestruder. Project has moved on to its own pulley and spacers.

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Updates:

B04 - Interlocking stubs align motor gear plate to extruder body.

B05 - Increased pulley / wall clearance at bottom of gearbox. Strengthened motor mount.

B06 - Removed split motor plate gearbox variant. In my judgement, it excessive flexes. Also, I have removed support material enough times from inside the motor plate gearbox that I am you can do it.

B06 - Fixed regression blocking idler door clearance.

B07 - Fixed motor body interference with front gear plate
Fixed incorrect M3 nut hole sizes on gear plate
Now recommending 3 bearings instead of just two in front.
Easier support material removal with mod settings in 3mf file.
Added some build process photos.

B08 - Inset motor mounting bolts to help clear bolt heads of x-axis mounts.
Added accessory motor plate adapter for use of motors directly (without gearing) while modified extruder is installed.

B09 - Added retrograde motor plate option.

B10 - Minor motor fitment adjustment of retrograde motor plate
Added Bunny Science pulley and spacers. Fixed bunny blocking set screw access.

Reorganized 3mf file contents to make each more complete
Loosened fit of shaft spacers.

Added shaft cutting guides

Updated BNB Universal x-carriage to be ready for Short Ears MK3S edition. Intended to avoid future reprinting and re-installation of x-carriage.