Bunny and Bear (BNBSX) MKS3 Geared Extruder Assembly

Experienced builders can already proceed, but if you need instructions for generic tasks like attaching a cooling fan, PINDA or hot end, those are not yet in guide.

Print BNBSX parts in PETG with 4 perimeters, 5 top shells, 5 bottom shells, 20% gyroid fill. Bunnies suggest 0.15 mm layer heights for best surface appearance.

BNBSX Extruder Plated 3mf file has the extruder parts pre-plated including spares of fragile bits. (Files at https://www.thingiverse.com/thing:362699...)

Print BNB Short Ears X-ends for this extruder. (STL's included in this extruder project)

Print BNB Universal X-carriage for this extruder. (STL's at https://www.thingiverse.com/thing:361059...)

Clear out each 3mm screw hole with a 3 mm drill bit to make bolt insertion easier.

There are also a few 2 mm holes to drill.

Draw nuts into hex pockets rather than trying to push them into position.

Be sure nut is rotationally aligned with hex recesss as you draw it in. Misalignment will damage the pocket.

Washer at bolt head reduces damage to plastic. This is especially important on the motor plate gearbox. Do not over tighten. Just get the nut fully seated. Once nut is seated, remove bolt and washer.

Printed parts mate together more accurately and securely if their mating surfaces are actually flat. Less torque is needed to secure parts whose mating surfaces are in good contact.

Flatten mating surfaces that were printed on textured print plates by wet lapping with wet/dry 600 sandpaper on flat glass plate.

Remove retraction zits from top surfaces or irregular shapes with light strokes of a metal file. Just one or two strokes are all you need.

Be mindful of raised features like index pins when flattening surfaces! Do not damage raised features

Bunny Science enhanced versions of the Bear x-ends are provided with BNBSX extruder. These "short ears" x-ends feature...

Low profile bearing mount clamps that don't obstruct the BNBSX extruder's rearward positioned motor.

Linear rod removal assist pusher bolt feature

Bear x-axis easy belt tension adjust system

Clear out linear rod mounting holes with 8 mm drill at low RPM.

Draw in M3 nut for each x-end clamp WITHOUT LMU8 bearings in place. Leaving out the bearings is VITAL during this step. This lets two sides of clamps abut and support each other during process.

Repeat for other x-end.

Insert M3 hex nuts to later accept T-nut mounting screws.

Repeat for other x-end.

Motor X-end has hex pockets at end of each linear rod hole. Draw one M3 nut into each pocket.

These nuts can engage a long M3 screw to help eject rods. Alternatively, use variable speed drill to spin linear rods in/out.

M3 x 8 mm CAP head screws to secure bearing clamps. Snug, but don't torque tight.

If using hex head M3 screws, you may need to file the top clamp screw head to clear motor..

Remove retraction zits and other irregularities from flat mating surfaces.

Two strokes with a metal file is usually enough.

Prepare 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:359520... for shaft cutting guide and instructions

Shaft_Cutting_Guide_Bunny_and_Bear_Short_Ears_55-9-42_mm is the cutting guide for this BNBSX "Short Ears" MK3S extruder

Ideal BNBSX gear shaft is slightly shorter at 53.5 mm, but cut at 55 mm and adjust after test fitting. BNBSX differs in that it needs clearance beyond rear of shaft for internal sensor lever.

Draw two 1050ZZ Miniature Steel Bearings 5x10x4 mm into front and back bearing mounting holes

Use M5 bolt, two washer, and a nut to draw in bearings. Resistance to bearing insertion should be moderate. If you find yourself torquing bolt hard, something is awry. Remove the bearing and recheck for stray filament bits

Front bearing is easy, but rear bearing requires drawing against uneven surface. Use flat object or printed BNBSX Bearing Pressing Aid piece to support large washer evenly.

Pass a 5 mm shaft through both installed bearings. Shaft should spin easily. If not, back out the bearings very slight using a 5 mm hex driver as a punch. Adjust alignment and depth of bearings until you achieve free motion.

The bearings will not fall out. Shaft locks installed later will stabilize their depth in mounting holes.

Three regular M3 nuts and one M3 Nylock must be installed.

On the Motor Plate Gearbox, it is absolutely vital to use washers with your drawing bolt. Otherwise, head of bolt will damage these index depressions around the bolt holes. Damage makes mating motor plate with extruder body difficult.

M3 Nylock for idler door bolt. We use Nylock here because idler door bolt is not secured under tension. It needs Nylock to help keep it in place.

Regular M3 Nut

Regular M3 Nuts, but be mindful of excessive bolt length during drawing in process.

Extruder Body is printed with an intrinsic support. Remove intrinsic support with knife and pliers.

Lap rear surface of Extruder Body to flatten its x-carriage mating surface.

Use metal file to knock off plastic zits on front mating surfaces. Be mindful of the three index pins

Install three M3 nuts. These will attach extruder to x-carriage.

Lower M3 nut is easy to install

Upper two M3 nuts are more challenging. Begin with M3 x 12 mm screw and washer. Partially seat nut with longer 12 mm screw. Switch to shorter M3 x 8 mm screw to fully seat nut.

M3 Nylock goes here for version B03.

Insert hot end cover mounting M3 nuts. These nuts must be fully seated and not protrude beyond rear surface of extruder body.

Top cover M3S nut

PINDA mount used M2S here in older versions, but made PINDA clamp prone to loosening after several hundred hours printing.

E3D Plenum Plate is held in position by a tab on each of its ends

Hot fin can be printed in higher temperature material like ABS or Polycarbonate to better resist heat. Another strategy is to have spare hot fins pre-printed, but higher temp material is recommended option.

Two M2 x 12 mm screws attach hot fins to extruder body

E3D Plenum Plate is omitted and special hot fin used if Mosquito hot end is installed.

For stand-alone, single filament use, armature with bearing detects filament ABOVE Bondtech drive gears.

For MMU2S, internal lever senses filament separating Bondtech gears. MMU2S uses this to know when filament has reached drive gears.

Press pivot MR63ZZ 3x6x2.5 mm miniature bearing into BOTTOM of armature.

Attach filament sensing MR63ZZ bearing to armature with M3 x 6 mm screw. Bearing should be secure but keep screw loose enough for free bearing rotation.

Insert armature into sensor pocket of extruder body

Secure through pivot bearing with M3 x 8 mm screw. Be gentle. This screw threads directly into plastic.

Insert small, 5 x 10 x 2 mm magnet, from Prusa MK3S sensor system, into pocket right of armature

Bunny Science needs only a single magnet. Magnet pulls bearing into filament path. Filament pushes bearing out of path and swings armature. Interruptor fin triggers MK3S IR filament module (to be installed later)

Internal sensor lever is sensor configuration for MMU2S printers. This replaces bulky external chimney with internal lever.

2 x 5 x 10mm magnet from Prusa MK3S sensor system

MR63ZZ Miniature Steel Bearing 3x6x2.5 mm

Internal sensor lever for MMU2S

M2 x 16 mm BLACK STEEL ALLOY screw cap hex screw. This screw MUST be strongly attracted to magnet. Stainless steel will not work. Also, use cap head here for needed compactness.

Optical interruptor bar should be printed in opaque color, preferably black.

Use sharp blade and /or emory board to clean stringing from optical fin. Try not to alter fin dimensions during cleaning.

Small leg of the fin does the actual optical interruption. It drops down and blocks light path when filament slightly opens idler door.

Use 2 mm drill to clear screw bore of optical interruptor bar. M2 Screw must readily slip through the bore.

A real hex driver is essential. Attempting insertion of the M2 hex cap screw with an Allen key is guaranteed failure. Depending on your screw head, use a H1.3 or H1.5 from a micro-screwdriver kit..

Press bearing into bottom of sensor lever.

M2 black alloy screw will be used to mount optical interruptor bar on lever at 90 degrees. Pre-threading the mounting hole makes things easier later.

Thread M2 screw into sensor lever. Keep screw perpendicular as you thread it in. Once hole is completely threaded remove the M2 screw.

Slide sensor lever into extruder body.

Temporarily secure lever with M3 screw and nut.

Attach optical interruptor rod to sensor lever. Its end has a shallow wedge shape to help with alignment. Rear of extruder body has opening through which a finger can support the lever

Insert 2 x 5 x 10 magnet into magnet pocket below optical interruptor bar. If you previously had magnet positioned for armature, move the magnet to this pocket.

Magnet pulls M2 screw downward and makes optical fin block IR sensor. When Bowden drives no longer have filament between them, idler door closes further and swings lever upward. How far it lever moves is fine tuned via a screw on idler door.

Here is the internal filament lever sensing filament at Bondtech https://www.youtube.com/watch?v=YfuO-00C...

When the internal sensor lever is in use, no armature bearing prevents filament exiting the opening formerly occupied by the armature bearing. Installing a filament path insert closes that hole.

Position the filament path insert into motor plate. It is easier to handle with tweezers.

Secure filament path insert with M2 x 6 mm screw.

Sight down filament path and adjust insert position so filament path is enclosed but not constricted.

Now that the lever or armature pieces are in place, it is time to test fit the IR sensor module

Gently position Prusa IR Filament Sensor module and secure with M2 x 6 mm screw.

Verify that optical interruptor fin moves in/out of IR sensor optical path.

This IR sensor module has an LED indicator modification soldered onto it. Bunnies enjoy easier system testing with LED lighting up when filament is sensed. https://forum.prusaprinters.org/forum/or...

1K ohm total of series resistance.

LED in series with resistors. LED and resistor attach to V+ and Output of filament module. This requires some skill with surface mount soldering, but is a very useful modification.

After verifying fit, it is a good idea to remove the IR sensor module and set safely aside extruder assembly is complete. It is possible to leave it installed through the process, but it is safer to temporarily remove it.

Addition of LED indicator to IR filament sensor board simplifies calibration and troubleshoot. Adds LED with 1K ohm series resistance between +5 to Out.

512 ohm resistor. One end soldered to +5

512 ohm resistor. One end soldered to Out

Solder LED across far ends of resistors. This completes electrical connection and physically holds LED in place.

Bench test by connecting +5 and Gnd to power regulated 5 volt DC supply. Have power supply POLARITY CORRECT or you will destroy sensor. Interrupting optical path will light up LED.

Chanzon (5 Colors x 20 pcs = 100 pcs) 1206 SMD LED Diode Lights Assorted Kit https://www.amazon.com/gp/product/B01CUG...

McIgIcM 1206 SMD Resistor Kit,1206 SMD chip Fixed Resistor Kit https://www.amazon.com/McIgIcM-Resistor-...

Intrinsic supports in gearbox preserve printed geometry of critical overhang areas. Formerly, slicer generated supports were used, but the new intrinsic supports yield cleaner results.

Motor plate has four M3 bolt holes that are printed with a thin, sacrificial membrane to improve print geometry. Clear out the holes with 3 mm drill.

Support material inside and around bearing holes must be fully cleaned out. If necessary, pass a small, flat screwdriver in from opposite bearing hole to scrape things out.

Hot End Cover

E3D Plenum Plate

M3S square nut for fan mount

Hot End Hot Fin

M3 nut for fan mount

Nylock M3 nut for fan shroud mount instead of regular M3 nut. Nylock helps prevent gradual fan tilt as screw loosens.

Two M2 x 12 mm screws

Hot fin holds E3D plenum plate via tabs and grooves. Do not over-tighten M2 screws. They are threading into only plastic.

Updated hot fins have pocket here to accept "Evan" hook of fan shroud. Hook supports right side of shroud even if screw loosens.

Insert M3S into slot.

Advance M3S to upper hole for regular fan position.

Push further into pocket to lower bolt hole for Volcano.

M3 Nylock for fan shroud

M3 nut for cooling fan.

You may now test fit complete hot end cover against extruder

Embed M3S square nut and M3 x 4 mm set screw into pulley. Leave set screw out far enough to permit easy gear shaft passage.

Multiple shaft hole diameters are supplied. Best fit is one that just slips on shaft without loose wobble nor excessive tightness. Usually about 5.20 mm will work. Note hole on flat side will likely print smaller due to elephant footing. Check fitment from top and carefully ream bottom to enable best fit without creating eccentricity

Embed M3 square nut and M3 x 3 mm set screw into each of two compact shaft locks

We assemble motor plate gearbox from parts previously prepared.

BNBSX Motor Plate Gearbox with bearings and hardware already installed

Bunny Science 56 tooth 2GT pulley

Bunny Science Spacer

BS compact shaft lock x 2

GT2 140-2GT-6 continuous loop timing belt

16 tooth GT2 drive pulley

Bondtech drive gear (with set screw)

STEPPERONLINE Nema 17 Bipolar Stepper Motor 0.7A 13Ncm (18.4oz.in) 17HS10-0704S

55 mm gear shaft with flats ground

Verify that shaft lock set screws are backed out so shaft freely passes through them.

Pass Bondtech end of shaft through front bearing.

Put two compact shaft locks on shaft. Tapered ends of locks should be directed towards bearing, Leave set screws LOOSE.

Pass shaft through 2nd bearing and another 2 cm further.

Put Bondtech drive on shaft. Align its set screw with flat and position so shaft extends about 0.25 mm beyond Bondtech.

Tighten Bondtech set screw

Slide shaft in/out to align Bondtech filament teeth groove centered with plane of filament path.

Secure shaft in this position with shaft locks. Each lock lightly touches its respective bearing and secures shaft in place.

Insert motor into motor plate gearbox. Motor plate is notched and recessed for easy motor insertion. Do not secure the motor yet.

Loosely secure motor with three M3 x10 mm screws and washers. Leave the screws LOOSE. You may need more than one washer if motor has shallow threading.

Add spacer to shaft. Flat side of spacer should be oriented up (away from gearbox).

Check that pulley and drive gear set screws are loose.

Hold pulley, belt and drive gear together and slide all three into position simultaneously.

Slide large pulley down shaft until it almost contacts spacer.

Align drive shaft with pulley set screw. You can do so by turning the shaft.

Tighten large pulley set screw. With motor and belt LOOSE, you can reach in above or below belt.

Align drive gear with belt and secure its set screws on motor shaft. Take care to engage motor shaft flat first.

Rotate motor on its pivot bolt to take up belt slack. You don't need to make belt super taught like the X and Y belts. It simply needs slack removed.

Secure motor in position with its bolts

Motor Plate Gearbox assembly is now complete.

Bondtech drive door has pocket for M3S square nut. Clear out the overhangs completely.

Bondtech shaft must be inserted in direction illustrated. It will not fit from other side. Fully seat the shaft.

M3 x 12 mm filament sensor adjust screw directly threads into plastic of idler door. This is used to adjust internal filament sensor system. For now, advance its tip to just flush with inside surface of idler door.

When filament sensor adjust screw is correctly set, it minimally extends beyond idler door. This picture show how little it will extend after calibration. For now, leave its tip flush with idler door inside surface.

Hot End Cover mounting screws must not protrude beyond rear of extruder body. B02M8 and newer use standard M3 x 30 mm. Older required custom 27 mm long.

Lower center extruder body mounting screw can protrude into plenum. This is especially problematic if wider, Mosquito hot end is installed.

Motor plate mounting screws protruding into motor bay impinge on motor body.

Hot end cover M3 x 30 mm mounting screws are critical length.

After verifying proper fit, remove hot end cover. We will re-attach it when installing hot end.

Prepare BNB Universal X-Carriage using directions at BNB Universal X-Carriage

If you have not already done so, add BNBSX spacer to back of Universal X-carriage. Its index pin should snap into the carriage.

There are three critical length screws extending from back of x-carriage into extruder. Do not install them now, but remember these places to check during assembly later.

M3 x 30 mm (location from front, upper left motor bay)

M3 x 16 mm (location from front front, lower left motor bay)

M3 x 8 mm CAP head screw. (location from front, lower, middle plenum)

Insert two M3 x 12 extruder body mounting screws, but leave them slightly loose.

M3 x 30 mm motor plate mounting screw. Optionally, grind this to 27 mm for easier motor plate removal.

M3 x 40 mm idler door hinge screw. Just insert this one, but don't engage its Nylock yet. We are inserting now only to help with alignment.

PTFE tubing for hot end are best sculpted for optimal filament constraint using Bunny Science PTFE Sculpting Guides for Tight Filament Constraint

https://www.thingiverse.com/thing:381979...

Sculpting PTFE to closely match Bondtech drive gears improves flex filament handling capability.

If single filament armature sensor, place 1050ZZ bearing on hinge bolt as spacer in place of internal sensor lever.

if MMU2S internal lever, hinge bolt goes through lever bearing then idler door

Secure tip of hinge bolt in Nylock, but don't tightly tension the bolt. It must not deform the plastics.

Use your finger and check that drive shaft Bondtech does not wiggle on drive shaft.

Close idler door and hold it shut with a finger. Feel the door for motion as you rotate gear shaft through several rotations. If flat is too shallow, you will feel screw impinge idler Bondtech and slightly open door during each rotation.

If you find impingement by Bondtech set screw, disassemble motor plate gearbox and correct shaft flat depth now. Extruder will not work reliably unless set screw is secure at correct depth.

Insert idler door tension adjust screw and spring. Only one screw and spring are used in BNBSX.

Use two M3 x 18 mm screws and LOOSELY attach parts cooling cooling fan. You can add a M3 washer to lower right screw, but not to top screw.

Shave top of fan mounting tab with Xacto knife. Reduce its top by down about 0.75 mm. Only front portion 10 mm needs modification. Fan plastic shaves readily and controllably. Remove only enough to clear belt.

Fan shroud attached to hotend cover via single M3 x 10 mm screw.

Current fan shroud has interlock "Evan" hook to secure right side of shroud to hot fin. hook prevents right sided downward tilt of shroud should mounting screw loosen.

Engage hook with hot fin while simultaneously slipping shroud over fan outlet.

Place a piece of paper on print bed. Nozzle tip must be clean and printer powered off.

Manually lower x-carriage until nozzle tip just touches paper.

Completely loosen PINDA probe

Place PINDA probe squarely upon 0.8 mm thick PINDA height gauge. https://www.thingiverse.com/thing:355564.... If you lack a gauge, a zip tie is usable, but sometimes a bit too thick)

Clamp PINDA in position.

Turn printer on and raise Z to bump against top stops to level x-carriage.

Top covers supplied for stand alone, MMU2S, PC4-M6, PC4-M10, and Pallete 2

4 mm x 10 mm long, top cover PTFE tube for standalone cover should be internally chamfered on both ends.

Orient two upper and one lower LMU8 bearings each with a bearing row up. (You cannot see row positions inside the bearings now, but we marked the row locations during x-axis assembly.)

Get your screws and driver ready now. You will only have one hand during next step.

2 of M3 x 12 mm (top row of screws)

3 of M3 x 18 mm (bottom row of screws)

Align x-carriage (with attached extruder) onto all three bearings. Hold in position while securing top x-carriage top cover.

Gradually and evenly tighten screws while checking that you are not causing any binding.

You should have already prepared the x-carriage belt paths but we will repeat instructions. There are two belt paths on x-carriage.

Use TOP belt path for Bear axis

Use Bottom belt path for Prusa axis

Add 4 tooth long segment of GT2 belt in unused path to reinforce thin, toothed plastic segments.

With tensioner bolts engaged but only screwed in 1-2 turns, insert x-belt NEARLY taught, but remaining loose. There is plenty of adjustment range. No need to stretch belt while putting into clamp.

In this step, we adjust the filament sensor to reliably detect presence of filament between Bondtech gears. Idler door must be tensioned during adjustments.

Insert filament into printer and advance it through Bondtech drive gears. The idler door will swing slightly outward when filament is between drive gears.

Display filament sensor state on LCD during this process. Better yet, watch LED indicator If you have installed LED indicator mod on IR sensor board,

Turn M3 sensor adjust screw on idler door CLOCKWISE (in) until sensor indicates no filament (LED goes off). Just two or three revolutions should be max.

Turn M3 sensor adjust screw COUNTER-clockwise (out) until sensor starts indicating filament is present. Continue another 1/2 to 1/3 counter-clockwise for reliable detection.

Test setting by removing and reinserting filament between Bondtech gears.