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Bondtech BMG Upgrade MK3S FDM printable new sensor integrated

by MarcoZ76 Mar 4, 2019
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Hello Marco, thx for the reply. I'm printing parts for your design with the Mosquito option right now and will be ordering all of the other parts today. Just wanted to make sure which stepper to go with. It'll be several weeks before I complete the update to my Mk3 with this extruder and hotend. I'll let you know how it works out.

Phil D.

Hello Marco,

Why did you use a 0.9 degree stepper vs. a 1.8? I might be wrong, I thought Bondtech used a 1.8. Do you have to make a firmware change for e steps for this upgrade?

Phil D.

Hi, you can use 1.8° as well. Probably it work better. I use extruder stepper from LDO with 0.9° that in theory should give you better details when you print, but because the einsy board can’t handle more than 600 step you have to reduce the microstep to 8 with 0.9° and to 16 with 1.8°. Both step are at 415. Actually i’m using the community firmware with LA1.5 from vertigo235.

Hi Marco, thx for the speedy reply. Yes, I did see that design and wasn't quite sure it would work, but after another read, it's the one I've been looking for.

thx again,
Phil D.

Hello Marco, I'm planning a Bear upgrade to my Mk3. I want to include a Mk3S extruder upgrade, Bondtech gear drive, and a Mosquito hotend combo. Your design (BTW, thx for a great job) comes closest to what I want. I assume it is designed for a E3D V6 hotend. Do you have any plans to modify it for Mosquito? or could I take it as it is presently designed and add Chris Riley's E3D V6 to Mosquito adapter (https://www.thingiverse.com/thing:2994065) for my needs?

many thanks,
Phil D.

Mosquito hotend adapter for E3D V6 mount

Hi Phil, i suggest to use this: https://www.thingiverse.com/thing:3652205 . Is a remix of my design with better integration for mosquito.

BMG Extruder for Mosquito Hotend and MMU2S

I was thinking about trying this. Looking for peoples thoughts over stock MK3S extruder. I got a Palette 2 Pro and have been having issues with jams in PTFE tube in the hotend of the stock Prusa.

I have remixed the Bondtech BMG Bear X-Carriage for MK2.5S printers. It is at https://www.thingiverse.com/thing:3692820

Bondtech BMG X-Carriage for Prusa Bear MK2.5S

include step or f3d files for remix with bltouch plz

Step files is included

Does your extruder not require the ball bearing for the shaft assembly just like the original extruder?

It requires as the original design.

Please add it to the BOM of the internal parts, I'm sure it is easier to get all the parts information from your page instead of looking over at Bondtech as well and deciding what is needed and what not.

The BOM of the internal part are already in the description from day one....

The required bearings are clearly missing.. from day one.

You are right!!

I have other improvement requests as well:

  1. Could you possibly modify the sensor cover so it can be used without a pneumatic fitting? The fitting is only useful if you're using the MMU, other than that it has no point. And for the MMU users you could also add a version that uses the original Festo QSM-M5 pneumatic fitting. I'll be happy to do my part and modify the sensor cover if you have no problem sharing the original file.

  2. In the print settings box you have added that supports are required. It would be nice if you'd let people know which parts exactly and what areas require supports. I personally think that only the Fan_Mount.stl requires supports but on the other hand I have found some difficult to print without supports areas in the extruder parts (check the attachment). Well not that difficult, but I'm pretty sure the circles will droop and will only make it difficult later for the square nut to slide in. It would be nice to modify those areas and use the rectangle method that Prusa uses on their parts which will make printing those areas no problem.

Try this one sensor cover without Pneumatic fitting

Hi! i just upload the part you suggest to use the square method for the vertical holes. Thanks

Careful! You have added the squares on the other side to the hole where they are not needed. I was able to identify multiple holes that require this square method, check out my screenshots. There are 4 holes in the extruder_front and one hole in the other part.

They seem to be fine now.

Thanks for the suggestions, i do same error because i'm going in airport within 1 hour, back to Italy from Korea after a long trip, i'm really tired...
Anyway let me know if any other modification need.Thanks again

I appreciate it, thanks!

  1. the sensor cover i designed for pneumatic fitting is used with Reverse bowden system. You are free to modify my design and share it with the same license, Step files are on files section.
    2.I personally use the support only on the "Fan support" and the "Extruder Body" where you attach the Hinge. Sorry actually i can't post i screenshot, but i wil do. For the part that you asked i initially used the support but in the final priting (with CF PETG) i didn't use and it was printed well (you can clean up with X-Acto knife). Anyway i will upload a new files with "rectangle method" soon. Thanks

Great work!
Will this work with the original MK3 also or is it an S only upgrade?

Thanks! But unfortunately it's only for the MK3S

Thanks for a blazingly fast answer!
I will revisit this once I take the leap on the S-upgrade :)

there seem to be 2 places to put the Pinda probe, do I use the front or rear hole for the probe for Prusa MK3S?

the front one for the MK3S

Does this project really match the MK3S? In MK3S the belt on the left is at a different level than the one on the right. Due to the different size of pulleys.


Hi, this extruder is made for Bear X-axis version.

Thx. Now I get it.

Ahh yes, I see! Thanks for the quick response.

But, while you are on line, I noticed a few other minor problems

  1. the upper right mounting bolt for the motor -- the screw head interferes with the gear teeth. I had to leave the bolt out. Maybe you could recess the head further.

  2. the primary (fixed) filament gear does not have enough clearance for fit. I needed to make a slight trim in the upper outer quadrant. I think about 0.1mm should do the trick.

  3. the head of the lower left motor mount bolt is very slightly too large for the recess in the front plate. Adding 0.25 should fix it.

  4. from looking ( I am not sure) but it seems that the clearance for the PTFE locking ring is too small. When I place the heating unit in the body it pushes the locking ring down and unlocks it. I think it needs 0.8 mm more to prevent this from happening.

Hi, yes the upper right mounting hole for the motor is unusable for most, i used a special bolt, i will remove soon from the design for not creating confusion. The fixed gear is perfect fit for me, just tu push a little when you are try to insert it and then it will have enough room to rotate. For all the other your issue i don’t know sincerely, i have 3 printer now working with this extruder design and all 3 work super well!
Remember that this is design is a proprietary Bondtech, i just make some modifications to make it printable with FDM 3Dprinter, i didn’t touch the parts where you found issue. When you print this kind of things your extruder must be calibrated 100% (extrusion multiplier)
Anywayit work really well, on AliExpress some famous copy brand like triangleLab is selling my extruder (without permission...)

thanks for the quick reply and considering my ideas. I am sorry your ideas have been stolen for financial profit - I hope this does not discourage your very fine efforts.

as to #4, I did several insertions and there seems to be good clearance for the locking ring.

I have printed this and I can not figure where the thumb screw thread is supposed to anchor. The thread goes into a blank hole.

there are two version of extruder body: one used the brass threaded insert, the other it used s quare nut. If you don't have a threaded insert you have to print the other. you have to read well all the info and update in the description

Is this design compatible with the original BMG parts? IE, can I re-use the front part and just print the back part (the part the changes the sensor) and carriage to convert over to the MK3S?

Can you recommend a fan shroud that works with this? I tried the RHD with BMG support but it doesn't fit :(

I found that this front fan support https://www.thingiverse.com/thing:3429508 works great with RHD nozzle shroud and with your model.

MK3 Nozzle RHD Rev. C Support for FDM Printable Bondtech BMG
by knoopx

Yep that is the one that I am currently using! Thanks

Why is there a reason why the cable guide in two pieces?

I don’t know, maybe for be better printable... but this question you have to ask directly to Grégoire Saunier, the creator of Prusa Bear.

Your latest updated file Bondtech with square nut has a problem. When I load it into Slic3r it says there is an error. I need to fix the file with Slic3r before it will print. Please look at your compile of the stl file.

i checked and from my side there aren't problems. The stl files has no problem. Try to re-download agian and use the lastest Slic3R PE 1.42.0 beta .

I did another download and this time there was no problem. Sorry, just some weird thing in my end.

Anyone else have issues with the lever from Bondtech for the filament sensor?

In fact you don’t have to use the original from Bondtech AB but mine modificated, you can find it inside the Step files. In any case i will upload the stl file here so everyone can print it directly without passing from fusion 360.

Unfortunately, the hole for the new filament sensor ball bearing is not designed for FDM printing and also is too small (8mm), the ball bearing (8mm ) can't move free, you have to push it to fit.

I used a 7mm ball and it fits perfectly. Works well too.

The hole is designed for FDM print infact it is an add-on that you can download directly from the creator Bondtech AB. I just integrated it inside the original design. Probably you have to set the EM (extrusion multiplier) or to have better settings in term of bridging.

Bondtech mad mistake, you can't design 8mm hole for 8mm ball, you need 50-100um for clearance or even more

The ball is 7mm not 8mm. Before say something wrong check it first. i attached the image

I see, then I got wrong ball, 8mm one.

Any chance for a MMU2S-compatible version? (With the new optical sensor sensing not the filament via an independent lever, but rather the door opening as the bondtech gears are pushed apart by the filament. MMU2S needs to know when the extruder gets a grip on the filament.)

Hi! Cause i don’t have a MM2S i can’t do it, i could not test it. For sure there will be others that can be mixed my design and integrate the MM2S new sensor door system.

Comments deleted.


congratulations, great job. Only two details, the up-right motor screw (view from front) is unusable, it hits against the white wheel, and I have had to make the motor pulley hole a bit bigger and shaft hole deeper, because the pulley and shaft hits against the walls of the extruder_front piece. Once I solved these issues it works awesome. I will publish my make in few days. Thank you for your remix!!!

Hi JuanPuchol, thanks for your feedback very welcome! About the upright screw hole probably for me it is good because i use a small size head screw. For the other issue it’s very strange because the design is the same of the original one and for me i haven’t this problem. Did you check the extrusion multipler before print it, probably you have overextruded.

Yes, I imagined you are using a small head screw, I have used standard (Prusa) screw. By the other hand, It is not overextruded, I had a strange noise that I have solved increasing slightly the pulley and shaft margins, I don't know exactly what's the problem,because I have the original MK3 Bondtech Extruder and I know it is the same design. Thanks again. Are you thinking to do a MMU2S adaptation?, I mean the IR sensor detecting the hinge movement.

Is this compatible with X-Ends and Tensioner MK3 MK2.5 by vekoj Jun 12, 2018 or the Bear X-ends?

Yes but you have to print this X-carriage https://www.thingiverse.com/thing:3472470 if you want to use Vekoj X-axis, (Zaribo version is same of Vekoj) Otherwise if you are using Bear X-axis then you are ok to print the X-carriage of this design

Zaribo X-carriage mod for Bondtech_Prusa_mod MK3S-MK2.5S new sensor
Comments deleted.

Did you put in the brass inserts when you printed this?

You put the M3 brass insert after finish print, you have to heat the brass insert then push it into the hole

will the original Bear carriage work with your design?

No, because there is a little open for Molex connector in my design