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Geared extruder mod for MK3S extruder integrates the Bunny Science Gearbox with the Butterworth design (Nathan Whitchurch) N4 and N4A (indirect laser) versions of MK3S extruder.
Antegrade = motor runs in normal direction, shaft pointed to back of printer
Retrograde = motor runs backwards, shaft pointed to front of printer
Six variants are supplied
- N4XT MK3S sensor, retrograde motor
N4XT indirect laser, retrograde motor
- N4 MK3S sensor, retrograde motor
N4A indirect laser, retrograde motor
- N4 MK3S sensor, antegrade motor
- N4A indirect laser sensor, antegrade motor
The retrograde variants place motor mass closer to x-axis as in the Bunny and Bear Retrograde option extruder.
Unfortunately, due to interference with the indirect sensor mechanism, it was not possible to move the motor 4 mm further back for indirect laser versions.
The N4 or N4XT Retrograde options with their maximal motor mass setback would be my choice.
The N4 motor plates can be interchanged with each other. They share a common extruder body.
Similarly, the two N4A motor plates can be interchanged.
You cannot swap N4 with N4A motor plates as the N4 extruder body and N4 extruder body differ from each other.
Butterworth versions were used as bases because he corrects the Prusa R4 MK3S filament path.
Bottom hot end fin opening diameter were tightened to 22.4 mm
Bunnies have supplied only the parts modified or added to implement geared drive. You will need the rest of the extruder parts from the original Butterworth designs. See https://www.myminifactory.com/object/3d-print-86329
Advantages of Bunny and Butterworth Geared MK3S Extruder
Improve extruder uniformity via gearing like Bunny and Bear, Skelestruder or BMG extruders.
Reduce extruder mass by about 70 gm compared to stock motor.
Move motor 4 to 14 mm closer to x-axis than possible with just the Bunny Science Gearbox. Reduces moment arm by moving motor closer to axis.
Upgrade replaces extruder body, motor plate, and idler door. You will need some MK3S extruder parts like x-carriage, back clamp, PINDA clamp, tail, etc.
Motor plate / gearbox MUST be printed with supports. 3mf file supplied with suggested plating and support enforcement block for N4 variants. 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.
NO - YOU CANNOT PUT THE MOTOR PLATES FROM THE BNBTR PROJECT ON A STOCK PRUSA R4 EXTRUDER BODY. The BNBTR includes a filament path correction. Although the motor plates may seem to fit, the path difference will crush your PTFE tubing.
Build with THREE shaft bearings. 3rd bearing goes in rear of extruder body and optionally adds extra shaft support.
see https://www.thingiverse.com/thing:3595205 for shaft cutting guides and instructions
Antegrade shaft (both MK3s and Indirect Laser Sensor)
1 x 5 mm shaft rod shaft x 44 mm long, grind two flats 0.38 to 0.4 mm deep
BNBTR Antegrade (both MK3S & IDL use same shaft)
Length 44 (3 bearings)
Pulley Flat 0 to 15 mm
Bondtech Flat 28 mm to end
The retrograde versions require longer shafts. Please verify length and shaft flat locations. They are as below
BNBTR Retrograde MK3S sensor
Length 61 mm for 2 bearings (Optional 65 mm long if 3 bearings)
Pulley Flat 0 to 9 mm
Bondtech Flat 50 mm to end
BNBTR Retrograde IndirectLaser sensor
Length 65 mm for 2 bearings (Optional 69 mm long if 3 bearings)
Pulley Flat 0 to 9 mm
Bondtech Flat 54 mm to end
3 x 1050ZZ bearings
1 x continuous loop 140-2GT-6 Timing Belt
3 x M3 square nuts
3 x M3 set screws
M3 hex nuts & bolts (various lengths from 12 to 30 mm long. Some must be cut to custom length during assembly)
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.
If building a retrograde motor plate option, cutting gear shaft shorter to engage only front 2 bearings reduces friction. The standard motor plates are not as deep and may benefit from the 3rd bearing. On the other hand, the BNB bolt on gearbox functions well without a 3rd bearing.
You MUST also set e-steps by sending g-codes to printer
Pulley gearing inspired by Skelestruder
Added N4A indirect laser variant
Added standard (non mmu) idler door
Main extruder bodies and motor plate gearboxes now have index pins to assist with alignment.
Increased cable passage clearance.
Added Bunny Science pulley and spacers
Added retrograde motor plate options.
B04 Stronger Bunny Science pulley
B05 Fixed retrograde motor plates to allow for bridging clearance sags.
Moved motor collar coving for easier motor insertion into retrograde motor plates
Tightened bottom cooling hot end fin opening to 22.4 mm
Added N4 extruder covers that also implement 22.4 mm change
B05a Extruder body index pins adjusted for easier motor plate engagement
Added N4XT retrograde versions for MK3S and indirect laser sensors.
B06 Removed redundant motor mount holes from retrograde motor plates.
Fixed interference with indirect laser assembly and motor plate
Changed shaft flat grinds to ends of shaft for easier alignment during assembly
Remove all support material, paying particular attention to bearing mount recesses. Stray support material left inside the recesses prevents free bearing function.
Once the majority of support material is removed, pushing shaft rod into each bearing hole to pop support material into gearbox.
Pass a small, flat screwdriver through opposite hole to clean out bearing mounts.
Flatten mating surfaces and motor mount. Uneven surfaces like the main extruder body and motor mount can be flattened with a file. Rear of motor plate can be lapped flat with wet sanding on a glass plate. Remove just high spots.
Draw in 2 M3 nuts at top of motor plate using standard bolt and washer
Press in two motor plate bearings with a bolt, nut and two washers. Outside washer should be 20 to 30 mm diameter. Inside washer (which presses agains bearing) should be just a bit larger than the bearing. Reach into gear cage with needle nose pliers or small wrench to stabilize nut while tightening bolt. Press just flush. Don't over tighten to point of deforming plastics.
Prep bearings by degreasing shipment oil and re-lubricate with light machine oil
Press in one bearing inside rear of extruder body. This one you can push in directly using a 10 mm Allen wrench or a similar diameter tool with flat end.
Check each bearing for free motion. The front bearing of the gearbox is the most prone to debris preventing free motion. Use special care cleaning out that mounting recess. If you need to remove a bearing, they can be gently tapped back out using a 5 mm Allen wrench as knockout pin.
Prepare main extruder body with embedded nuts as per usual MK3S instructions. Because there is no motor attaching to usual location of motor plate, the lower two motor mounting bolts are not used.
IMPORTANT: Most 5 mm shafts are slightly too large in diameter. If diameter of shaft is too large to easily slide through bearings, slightly decrease its diameter by chucking in drill and using fine sandpaper while spinning it. Make it just slide fit, not loose. The entire length of the shaft should be tested for easy passage.
- Shaft flats for pulley and Bondtech drive must be ground to depth of 0.35 to 0.4 mm. Grind lightly with Dremel and measure frequently. Notching ends of shaft to indicate flat positions greatly simplifies later assembly.
Antegrade Shaft and Pulley
Position one spacer upon flat side of large gear. Have small diameter side of spacer oriented away from gear.
Pass gear, spacer, and belt into gear cage using belt as handle. Align gear and spacer so they are centered with bearing holes. Press shaft into gear cage and through large gear, spacer and through 2nd bearing. Advance until shaft is flush or sticking out no more than 1/2 mm in front of motor plate.
Secure gear with set screw on shaft flat. You won't be able to see the flat. Align using notch you previously cut in front end. Thread locker is recommended. Don't rely on high torque. Too much torque will deform the plastics.
Prepare motor by grinding a flat on its shaft and attaching drive pulley. Position pulley as near motor body as possible without touching.
- Add motor with its pulley to gear box.
Retrograde Antegrade Shaft and Pulley
Prepare motor by grinding a flat on its shaft but don't attaching pulley yet.
Insert motor into gear box.
Insert rear end of shaft through front of large pulley. Front end of shaft should be flush with pulley front surface.
Place one spacer onto shaft behind pulley. Orient spacer so it's narrow diameter side is away from pulley.
Advance shaft through 1st bearing.
Add 1st shaft lock. Orient narrow tip end of lock towards front bearing.
Advance shaft further and add 2nd shaft lock. Second shaft lock should have its narrow tip towards second bearing.
Advance shaft through 2nd bearing. Keep advancing until large pulley is about length of motor shaft away from gearbox.
Add 2GT belt and motor drive pulley.
Advance shaft further while also slipping motor drive pulley onto motor shaft.
Position shaft to leave just a narrow space between spacer front of gearbox.
- Use shaft locks to to secure position of shaft. Each lock is to be placed against its corresponding bearing and set screwed in place. Once both locks are engaged, the shaft and bearings will no longer be able to slide in/out.
Continue with General Build
Secure pulley set screw against shaft flat.
Secure motor in position to take up belt slack, but not "stretched" tight.
Slide Bondtech drive gear onto shaft. Align its filament gripping teeth centered with rear surface of motor plate.
Cut two upper motor plate M3 bolts to proper lengths to not extend into belt path. Too short and they won't engage with embedded nuts. Too long and the ones on the left interfere with belt path. Bolt and shaft lengths are documented later in these instructions.
Attach motor plate to main extruder body. Motor plate assembly slides straight in. Alignment is easier if all mounting bolts are backed out flush with extruder body front surface.
Check that shaft enters rear bearing (if you are using 3rd bearing option)
- Recheck alignment of Bondtech is centered on plane between motor plate and main extruder body. Filament path is centered in that plane.
The below are best estimates for custom motor plate bolt lengths for flush fit.
Please check actual fit before grinding bolts to length.
n4a-xt-indirectlaser / n4-xt-indirectlaser retrograde
upper right bolt 35 mm
upper left bolt 35 mm
n4a-mk3 / n4-mk3 retrograde
upper right bolt 28 mm
upper left bolt 24 mm
n4a-indirectlaser / n4a-mk3 antegrade
upper right bolt 28 mm
upper left bolt 28 mm
CAUTIONS FOR RETROGRADE VARIANTS
Gear shaft is longer for retrograde variants.
Cut upper left motor plate mounting bolt so it does not extend from extruder, through motor plate, and impinge upon body of motor. This is vital to check before installing motor.
Retrograde version requires plugging in motor cable flipped 180 degrees at EINSY to reverse motor direction.