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BNBSX Extruder Plated B07.3mf
BNBSX Motor Plate Gearbox (35 mm) B07.stl
BNBSX Motor Plate Gearbox Standard (26 mm) B07.stl
BNBSXM hotend cover hot fin E3DV6 B06.stl
BNBSX bearing pressing aid.stl
This BNBSX "Short Ears" extruder for MK3S sensor is the edition needed for upgrading Prusa MK3S and MMU2S printers.
For MK3 printers, see instead short ears for MK3 printers. https://www.thingiverse.com/thing:3606189
Build guide is being written, but not yet complete. Complex and Bunny Science specific portions of BNBSX assembly are already in guide. Remaining, generic steps should be easy for experienced builders.
Advantages of this extruder over stock MK3S R4
- Geared 54:16 for more consistent extrusion. (54:16)
- Indirect drive isolates filament from extruder motor heat
- Corrected filament path/Bontech alignment (as in Bear extruder)
- Lower total mass by about 80 gm
- Extreme rearward motor position reduces moment arm
- Continuous PTFE path deep into extruder for MMU2S and Palette 2
- Two, swappable filament sensor systems (armature for single filament, internal lever for MMU2S)
- Internal filament sensor lever eliminates Prusa filament sensor chimney on MMU2S
- Internal filament sensor lever allows full opening of idler door
- Single screw tuning of MMU2S filament sensing
- New MK3S sensor armature design eliminates steel ball rattling
- Provisioned for LED filament sensor indicator mod
- Only one magnet needed for filament sensor
- Easy motor plate and hot end removal for service
- Separately printable hot fins for heat resistance
- Hot fins tightly encircle hot end.
- Replace PTFE, heater cartridge or filament sensor without full tear down.
- Fits E3DV6, Volcano, or Mosquito hot ends
- Air plenum optimum whether E3D or Mosquito installed
For comparison, the following are how far various extruders place motor from rear of extruder body.
MK3 R3 30.5 mm
MK3S R4 28 mm
Bear 27 mm
BNB Retrograde 23 mm
BNB Short Ears Edition 17.5 mm (with Bunny Science Universal x-carriage, 19 mm otherwise)
Because extruder motor is pushed so far back, this must be mounted on Short Ears version of Bear x-axis to clear the motor x-end. Normal Bear x-axis mounts will impinge against motor.
You can also mount on Prusa x-axis using the BNB Universal X-carriage, but the Prusa axis is much more difficult to tension properly.
Videos of BNBSX in operation
Filament armature detecting above Bondtechs. Optional LED mod indicates when filament is detected by either armature or MMU2S internal lever
Internal lever MMU2S sensor (M7 revision) undergoing bench test. I am manually turning shaft to move filament in/out of Bondtechs.
Essential to use the BNB Universal X-carriage when doing this upgrade. https://www.thingiverse.com/thing:3610593. BNB Universal X-carriage has cable management features to reduce risk of hot end cable damage during XYZ calibration
That carriage also lets you remove the motor plate WITHOUT taking off the back of the extruder.
**** Double check lead dress of hot end wires with x-carriage max left and print bed max forward BEFORE XYZ calibration. Verify cables do not contact print bed cable cover.
Build differences from the regular Bunny and Bear Geared Extruder...
- Short Ears X-Ends must be installed to allow motor to clear
- Compact shaft locks required
- Bunny and Bear Short Ears Shaft is different
Length 55 mm for 2 bearings
Pulley Flat 0 to 9 mm
Bondtech Flat 42 mm to end
If you do not already have a hot-end collet clip, print one from Bear extruder (https://www.thingiverse.com/thing:3226689). That STL is included here for your convenience.
Motor plate prints with intrinsic supports that must be removed. Also, trim away overhanging layer of filament that covers inner bearing mount. Time spent neatening up the layer printed as a overhang saves grief later.
Some support scarring will remain, but is largely hidden by installed extruder cover.
Build with two shaft bearings. No 3rd bearing is used for this extruder
5 mm diameter shaft rod
Length 55 mm
Pulley Flat 0 to 9 mm
Bondtech Flat 42 mm to end
see https://www.thingiverse.com/thing:3595205 for shaft cutting guide and instructions
5 of Bearings - 3x6x2.5 mm Miniature Steel Bearings MR63ZZ
M2 x 16 mm socket end cap screw, in black alloy to connect MMU2S internal lever to its optical interruptor arm. THIS SCREW CANNOT BE STAINLESS STEEL. MUST BE STRONGLY ATTRACTED BY MAGNET )
Remainder of screws are hex head, stainless steel
I suggest these sets of multiple sizes as you will may sizes of M3 from short to long.
Not the strongest hardware, but adequate for plastic to plastic work.
MK3S IR filament sensor kit
5 x M2 screws x 12 mm for hot fins and lower x-carriage cover
1 x M2 screw x 6 mm for MK3S IR sensor (Screw supplied with MK3S sensor is too long)
1 x M2 screw x 8 mm for optical path insert
2 x M3 screws x 8 mm for optical armature
2 x 1050ZZ bearings
1 x continuous loop 140-2GT-6 Timing Belt
4 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)
M3 Nylock nuts
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. Must plug into EINSY upside down to reverse motor direction.
You must also set microstepping and e-steps. Depending on which type of motor you have installed (usually 1.8 degree) the e-steps differ.
geared extruder, 1.8 degree motor (usual)
geared extruder, 0.9 degree motor
Note that M92 command must be issued AFTER M350 because M350 may alter prior M92 value.
Follow with power off/on and M503 to verify settings are correct.
Pulley gearing originally inspired by Skelestruder
Reversible motor x-end option inspired by Cristian2281 https://www.thingiverse.com/make:667387
Check motor x-end top clamp bolt. Depending on build tolerances, your motor may come into slight contact with the head of that bolt. If that is happening, file off a bit of the bolt head or change to button cap bolt (with smaller head profile)
Upper bolt tab of print fan likely to contact drive belt. Use x-acto knife to shave a bit of plastic from fan's bolt tab to clear belt. Takes just a few minutes to perfrom.
Recent Change Log
B03M6 - PINDA mounting clamp adjusted to better clear idler x-end.
B04M - Extruder main and extruder E3D pane modified to fit thicker Sunon 2510 fan on Mosquito
X-end idler modified to better clear older PINDA clamps.
B04M1 - Changed pulley to 54 teeth to reduce interference with parts cooling fan. This requires slightly different e-steps value (detailed above). 56 tooth pulley remains in files set because older gear plates may not have enough belt adjustment range to accommodate 54 tooth pulley.
Multiple 54 tooth pulleys with varying shaft hole diameters are supplied so users can select one that best works with their printer's extrusion characteristics. Best fit is one that just slips on shaft without loose wobble nor excessive tightness. Usually about 5.20 mm will work. Note that hole on flat side (printed on bottom) will likely be lower diameter than top due to slight elephant foot. Check fitment from top and carefully ream bottom to enable best fit without creating eccentricity
Motor plate BO4M1 has larger motor excursion range to allow 54 or 56 tooth pulley.
B05 - Motor plate gearbox prints with intrinsic supports instead of slicer generated supports. Simplifies post-print processing.
Added BSC RHD fan shroud.stl - a high volume fan shroud with front vent like that in BS4RHD fan shroud successful with Mosquito hot ends.
B06 - Motor plate reinforced to improve PETG resistance against warping under belt tension.
Hex pockets in motor plate and extruder main slightly enlarged to better accept nuts especially if printed in stiffer materials like polycarbonate.
Added bearing pressing aid to support washer against uneven motor plate surface during pressing of rear bearing.
Fixed internal void in hot end e3d hot fin
B07 - Bearing pockets modified for easier pressing.
Motor plate has pads at left end motor mounts to compensate for tilt of motor created by belt tension.
Plated 3mf file includes spares of the small parts like optical armatures, levers and interruptor rod.
Motor X-End has "Short Ears" to let motor clear.
Draw in the M3 nuts for the x-end clamps WITHOUT the bearings in place. This lets the two ends of clamps contact each other during the drawing in process. With the bearings in place, the ends cannot abut each other during the drawing in process.
CRITICAL * X-End Motor plate M3 BUTTON CAP screws for bearing clamps must be correctly sized. If they are too long, they will damage Z-axis screw. Should be about 8 mm. Double check that z-screw is not impinged during install.
Do not over tighten the screws with bearings in place. The clamps do not travel as far with the bearings inserted. They are not intended to close the gap. You risk breaking the plastic if you over tighten. Just snug the screws and no tighter.
Embed an M3 nut into hex recess at end of each rod hole before inserting rods. You can later use long M3 bolts to engage the nut and easily push out axis rods.
When routing motor cable, leave enough slack to route from front or below motor.
Do NOT route cable BEHIND the motor. That will pinch the cable between motor and the x-end.
Remove all support material, paying particular attention to bearing mount recesses and near filament path. Stray support material left inside the recesses prevents free bearing function.
Once the majority of support material is removed, tap shaft rod into each bearing hole to pop out support material.
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 4 M3 nuts for motor plate using standard bolt and washer technique.
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. Gearbox has uneven surface opposite 2nd bearing. Use a flat object as spacer to even out surface for washer to press against while pressing in bearing.
Prep bearings by degreasing shipment oil and re-lubricate with light machine oil
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.
IMPORTANT: Most 5 mm shafts arrive 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 0.38 to 0.4 mm. Grind lightly with Dremel and measure frequently. Use a shaft cutting guide to make the process easier.
Retrograde Shaft and Pulley
Prepare motor by grinding a flat on its shaft
Insert motor (without drive pulley) 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 placed against its corresponding bearing and set screwed in place. Once both locks are engaged, the shaft and bearings will no longer slide in/out.
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 motor plate M3 bolts to lengths for tips to be flush when fully engaged. Too short and they won't engage with embedded nuts. Too long and they can protrude and interfere with motor. See build guide for more info.
- Always with optical armature out of way slightly when attaching motor plate. A length of filament inserted into filament path will move armature out of way sufficiently. Motor plate assembly slides straight in easily. If there is resistance, verify optical armature isn't being crushed and idler tension screw is loose.
. Index pins help with final alignment of motor plate. Installation is easier if all mounting bolts are backed out flush with extruder body front surface.
- Recheck alignment of Bondtech is centered on plane between motor plate and main extruder body. Filament path is centered in that plane.
This upgrade requires plugging in motor cable flipped 180 degrees at EINSY to reverse motor direction.
BNB Universal x-carriage has two filament paths. Upper one is for Bear axis, lower one is for Prusa axis. Put 2 tooth piece of belt into unused path before inserting belt. The universal carriage also needs 8 mm bolt instead of normal 10 mm one middle of belt path.
Hot fins at bottoms of extruder body and hot end cover are to be attached via M2 x 12 mm screws. Once hot fins are attached, remainder of assembly is as usual.
Included hot fins and plenum inserts are used for E3DV6 hot end. The plenum inserts go into tabs of extruder and hot end cover before attaching hot fins.
See Mosquito compatability kit for Mosquito specific hot fins. Omit plenum inserts if using Mosquito hot end.
Main extruder body has a thin, intrinsic support where internal MMU2S lever will pass. That intrinsic support must be removed. A combination of pliers and knife are needed to fully clear it out.
Thoroughly clean support material from motor plate around filament path. There are lots of tiny support bits that must be fully removed. Be patient and get it all, especially that inside recesses.
Press bearing into optical armature from BOTTOM (the side away opposite fin). It should be barely inset from bottom of armature.
Pre-thread MM3U2S internal lever's optical interrupter bar mount hole beforehand. Trying to attach tiny optical interruptor's M2 screw without pre-threading is difficult. The M2 screw needs a H1.5 driver. Do not use the allen key supplied with the Amazon screw kit. A mini screwdriver kit's H1.5 bit is far easier to use and less likely to strip the head.
When mounting motor plate to extruder, don't crush filament sensor armature. The armature naturally swings beyond filament path when motor plate is off. To avoid crushing the armature, swing it out of way (towards IR sensor) and insert a piece of filament in filament path to push armature out of way until motor plate is installed.
In case it isn't obvious, you install either the filament armature OR the MMU2S internal sensor lever, not both at the same time
If MMU2S internal lever option is installed, a filament path insert can be installed in motor plate to close hole in filament path. Might run ok without the insert, but having the insert in place reduces risk of filament leaving path.
PTFE tubing of extruder must be shortened by 5.5 mm, like in MK3S. Remember, this extruder is short bodied like the MK3S R4.
For stand alone top cover, use 10 mm length PTFE tubing to guide filament into extruder body.
B03 has top covers and extruder body with full pass through of PTFE 5 mm into extruder body. MMU2 and Palette 2 owners should insert PTFE Bowden completely through top cover and another 5 mm into extruder.
B03 versions of top covers PC4-M10, MMU2S, and Palette2 have full pass through feature.
PC4-M6 and standalone do not. Those two require 10 mm PTFE segment.
No nylon washers are used with the idler doors.
Gear shaft should cut a little shorter than in Short Ears. The rear end of shaft should barely extend beyond Bondtech. Otherwise, gear shaft will impinge internal MMU2S sensor lever.
M3 bolt through bottom right of idler door adjusts MMU2S internal sensor lever system.
Completely clean inside idler door M3S nut recess before inserting nut.
If single filament sensor armature option, place a MR63ZZ bearing to right of idler, on its mounting bolt. Bearing will fill space that the MMU2S internal sensor lever would otherwise occupy.
Nuts for hot end cover bolts press into REAR of extruder body.
Nuts for connecting extruder to x-carriage press into front of extruder body.
M3 12mm bolts are inserted "backwards" into hex pockets of universal carriage to secure extruder body. Despite there being nut recesses in those positions of the universal carriage, do NOT put nuts into those pockets of universal carriage. Bunnies intentionally use those holes backwards for the BNBSX.
Parts cooling fan and drive belt are very close to each other due to 5.5 mm higher E3DV6 position. If yours is too close, shave a bit of plastic off fan's bolt mount with a sharp knife. It only takes just a few strokes.
Watch out for motor plate mounting bolts extending into motor recess. Those bolts must be cut to custom length to avoid impinging motor. Test fit the bolts and adjust lengths before inserting motor.
Top covers previously did not bridge well around LED observation port. They now print with a trapezoidal shaped, intrinsic support. The support cleans up the print, but it MUST be removed before using any of the covers.