MK3 Nozzle RHD Rev. C (Support for Bondtech BMG)

by RH_Dreambox Dec 2, 2018
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Hi - one of my biggest complaints on the prusa fan shrouds is that they block the view from the center to the print nozzle. Have you considered remixing this to have an arch or prism shape going along the center so that you could view the nozzle from the front?

Unfortunately, this is beyond my skill in CAD design. I don't know how that would impact airflow, but it would tremendously improve visibility from the front.

Yes, it would be great if you could see the tip of the nozzle during printing. But there is unfortunately one reason why I have not done any such.
The cooling fan has too low capacity and can not build up any greater pressure. Therefore, a reduction of the area in the ducts would greatly affect the air flow.
With a different design (see my Bear fan shroud) with only two outlets, one could make a small inspection channel. If you want to test a similar fan shroud, then you can find it here at Thingiverse, I just don't remember who did it :-(.

Hi espinetegg,
Your picture shows that you unfortunately installed Heatblock incorrectly. See my picture (I also have the original Bondeth)
You must first disassemble heating element and the thermistor. Then turn the Heat Block with nozzle and heat sink 180 degrees.
Then you can reassemble the heater and the thermistor.
But a great warning! Be extremely careful when doing this, as it is extremely easy to destroy the thin cables.

There are filaments behind your fan. How did it get there? Do you have a leak between Heat block and Heat brake?

you are right, thanks a lot for your time and great design.

Hi, I downloaded this nozzle fan for my MK3 with original Bontech extruder and I have an issue. It hits the E3D heater block and I cannot screw it because a gap.
What is wrong?

Thanks for your help and design

Is there a version of this that would work with the mk3s?
I'd love to use this!
The stock shroud is trash and I haven't found anything better.
I know alot of people are looking for a new shroud to their mk3s.

Ja munstycket till MK3S kallar jag för en "blåskanal" eftersom det inte styr upp luftflödet.

We'll see if I can look at it during the Christmas holidays, it should not be so difficult to adapt to the S model.

Tack! Hade varit fantastiskt!
Thanks alot man, that would save me from having to upgrade to bear axis and a while lot of work <3
I'll make sure to spread your design once it's up <3

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Printed your duct and it looks amazing! Only one thing.. the fan mount are either way off or I'm retarded not knowing how to mount it on my extruder.
Could you please contact me on facebook maybe? Or messenger.
My name is Mathias Mädz Lindberg.

That's awesome!
I'm going to try this during the weekend.
Thank you very much!

Hi Mathias,
I don't understand what you mean by the fan going too far out.
I now tried on an extruder R4 that I have printed for testing, and where the fan fit well.
See the attached PDF so that there is no misunderstanding of how to mount it.

i've mounted the support and the fan exactly as shown on the PDF but like you see on my pictures it dosent fit.. dunno if the fact that i have a LDO 5015 matters but should be the same measurements as the stock prusa 5015.. its like the 5015 isnt sitting deep enough into the actuall duct, if that makes any sense.

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I'm gonna look into it tomorrow, dont see why it shouldnt fit to he honest.
Must he me doing something wrong ^^

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Now everything fits, even tho it's a very snug fit.
It's like the top part of the support is sitting on the motor and making the entire duct end up.in an angle.
Not sure how it effects the print tho, I'm gonna try it now and hopefully it won't hit the print

Hi again Matthias,
Now I should be ashamed! When I picked up my old extruder motor I saw that it was 39 mm long and not 30 mm like the one I have in my CAD model.
I did not discover this because I no longer use Prusa's extruder (I use Bondtech today).
I apologize for this and I will redesign the nozzle and its support after the longer motor.

Hehe no worries man, I'm just happy that you're willing to spend your time and actually solving what I think many people have problems with.
Atleast on the mk3(s).
Looking forward for the finished model :)

The CS nozzle is now modified to fit your extruder.
I've uploaded the files so you can find them here at Thingiverse.


RHD CS Nozzle for Prusa MK3S

The CS nozzle is now modified to fit your extruder.
I've uploaded the files so you can find them here at Thingiverse.


RHD CS Nozzle for Prusa MK3S

3rd times the charm!
thank you so very very much for taking your time sir =)

That's brilliant! Thank you!
I'll print the parts once I get home and I'll see if they fit ( fitted with zip ties right now lol )
So far I can tell you that the duct are doing an amazing job!
Even tho its misaligned with the previous parts.
Let me get back to you once I've fitted the new parts.

By any chance do you still have any previous or test versions of this cooler with symmetric ducts between the left and right sides?

Also, how does this compare to your Bear extruder cooler for overhangs?

What do you mean by previous versions, do you mean Prusa original or other nozzles that I have tested?

As for overhangs, I have done some tests on different nozzles, but I have not been able to see any major difference in the result.
Strangely enough, the result was an almost perfect overhang when I switched from a quality filament to a simple and cheap filament!

Thanks for the reply.

I only saw you model after it was at "rev.C", so just wondered what rev A or B or anything before that was like. I don't actually own a Prusa, so the mounts didn't really matter to me. Like the picture that says "old nozzle to the right", do you still have the STL or STEP file for that old nozzle where the 2 sides are symmetrical?

I ran some overhang tests on this RHD Rev.C and overhangs are clean to about 70-75 degrees. 80 degrees wasn't too good, so if your bear extruder cooler was better, i thought maybe I should give that one a try instead.

Fan shroud Rev. C has a slightly higher air flow and a slightly smoother flow in the side outlets than previous versions.
Bear fan shroud has a vertically mounted fan on request from Gregsaun, the developer of Bear.

Of the response I received on the two nozzles, many prefer Rev. C.
It is extremely difficult to make good overhangs greater than 70-75 degrees. And it seems that the quality of the filament has a greater significance than any fan shroud you use.
If you make your own remix of any fan shroud, keep in mind that the location of the fan may affect the distribution of the air between the right and left sides.

i had printed the RevC nozzle out in PETG (gasp!) for my MK3 and really like the performance. (PETG is currently my hottest filament that I regularly print, still do most printing in PLA.) But ever since upgrading my extruder to the MK3S I haven't been able to use it and it seems to my very inexperienced eye that the stock MK3S part cooling duct is a step backwards (most of the air seems to be dumping on the front of the heater block, and there isn't as much side cooling) than even the last version of the stock MK3 part cooling duct.

I know in your earlier comments below that you aren't interested in adapting this design for every extruder under the sun. Does that also mean that you aren't interested in updating the mounting to be compatible with the stock MK3S extruder design? (The mounting screw is now one of the noctua mounting screws, so it comes in from the side.)

It is true that I cannot make a nozzle that suits all different variants of extruders.
In order for the nozzle to work well and get a good fit, I have to make a CAD model for each extruder so that I have a CAD model to work with.
It is a lot of work to do that and that is why I have waived some variants.

But when it comes to Prusa model S, I actually thought about adapting the nozzle.
I just haven't had time with this because I am now renovating our kitchen.
But give me some time so we'll see.

Thank you for the prompt reply, and the potentially positive message. I don't envy you going through a renovation process, but I do hope it is well worth it in the end.

Enjoy your new kitchen when it is finished.

I have a proposition to you to add mounting for regulated height for different nozzles. I have MicroSwiss nozzle which is longer than classic brass nozzle. Also I'm using silicone sock on the heater block and this gives me bootom line of your air nozzle abt 1.5-2mm over bottom line of heater block and 5mm or more over nozzle end. All air flow is locked by heater block. I think it will be nice to make both screws holes (BMG in my case) as ovals which give us possibility to move all down and find best position. I think 3mm will be enough but maybe 4mm ?

Also please tell me what height from bottom of "air" nozzle to bottom of printing nozzle did you used for your simulations?

Hi luczjanoo, and thanks for your suggestion.
I will see what can be done to use the air nozzle.
It's not as simple as just making an oval hole.
The fan must also be moved down when lowering the air nozzle.
I promise nothing, but I'll look at it.

I attach a drawing and a 3D pdf that you can watch.
The tip of the nozzle is placed 2 mm below the bottom of the air nozzle.
A silicone sock is no obstacle to the outflowing air.
I use silicone sock on my hotend myself.

Thank you for answer. I mean both holes needs to be ovals of course (in fan mount too). I'll try your .step file today but only air nozzle is uploaded. No fan mount.

If you used 2mm so I need to move 3mm down whole air nozzle with fan to get proper results.

I count on you but of course in free time :) Thanks a lot.

Now there are STP-files uploaded of the nozzle support.
But why are you using MicroSwiss nozzle?

This is the best cooling option i have ever used. (I have been printing for 8 years now.)

Thanks for the nice review! It encourages me to try to improve the cooling even more :-)

Does anyone know if this would be compatible with the full Bear upgrade MK3 extruder?

Any plans for a remix/update to fit the new R4 mount design? Thanks!

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Thanks man!
Printed in ABS (Titanx) and will test it.
I've upgraded my extruder to the Bondtech 3:1 version
So I had to design a new holder for the fan (the screw for the fan holder sits much lower)

But did you print the right nozzle support?
"BMG_RHD_Fan_Nozzle_Support.stl" (2019-01-31) is intended for that extruder.

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This is a great design, thank you for sharing it openly. I am gonna be using this for my own custom printer, could you tell me the relative position of the nozzle to this shroud? As in, how high does the bottom of the shroud need to be from the tip of the nozzle?

Hi pushpreet,
Here you can find the most important measurements.
Good luck with your printer!

This is absolutely amazing. Thanks a lot!

This is the file I printed from thngiverse Bondtech Prusa 3 Extruder - FDM Printable - MK3 \ MK2 BMG

Yes it is true, my nozzle and support are only suitable for Bondtech original details. The attachment point of this extruder differs from the original.
Unfortunately, I cannot make any adjustments for each new variant of this extruder.
Those who draw their own variants should consider compatibility with existing accessories.

Can you post your extruder files

I will post the extruder when I have evaluated and tested it. But right now I'm working with the nozzle.

Hi in order to use this with the bmg extruder for mk3 found on thingiverse which fan bracket do you have to use the fan bracket labeled bmg does not work with the nozzle gcode file you posted the bracket does not align with the hole in the extruder

This extruder I downloaded from BondTech's website. The picture shows it with my mouthpiece and associated support.
Does your extruder look like this?

That's not the official Bondtech BMG. The official BMG doesn't have the air slot that you see in the model in your screenshot. Here's the Bondtech model I pulled down. https://github.com/BondtechAB/Bondtech_Prusa_i3/tree/master/CAD-Files

But, you might not need to worry about it. I have the BMG and your shroud loaded up into F360 and I'm working on making the adjustments now. I'll post it as a remix once I have it done.

@Hotpocketdeath I'm sorry because it was wrong nozzle support. I found the files on Bondtech's website and thought they were the right ones. I didn't know they were at Github.

But big thank you for the Github link.
I have now made a new support that fits much better :-)

New version looks pretty good. I was thinking of going a different route for my own design, but it would have been slightly bigger.

I was thinking of another version to fit the printable version. https://www.thingiverse.com/thing:3347150. They'd be almost identical.

Bondtech Prusa 3 Extruder - FDM Printable - MK3 \ MK2 BMG

I was looking for such design! I am so happy to find it now!

hi, is possible to have a .step file of the fan duct?

STEP-file is now included in the file package :-)

hello, I made small changes, to make it weigh 1-2g less, a bit of externally chamfer and fillet in the interior walls to avoid air slamming in 90 ° angles, a little more space for the probe.
I do not know how to calculate the fluid dynamics, once on f360 there was the option but now I can not find it. Just for information if you have time you could check if the fillets inside change the air flow, or even simply tell me with which program you can do

Hi edo_drum,
Unfortunately, I cannot open Fusion files, I do not have that program.
My models is drawn in Autodesk Inventor, and I do simulations in Autodesk Simulation CFD. (You can download a 30 day demo version for testing.)

But I don't think your inner fillets will disturb the air flow. I usually insert small radii instead of fillets, but it is mostly to get a nice interior surface when printing the nozzle.
Then it is probably more important not to have too sharp bends in the air duct or to small ducts that increase the air resistance.

Regarding the inside and outside fillets, I will use it more on the new nozzle that I am now working on. Right now I am testing a nozzle of PETG to see if I managed to reduce the problem of drooping on left side, and it looks good so far.

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Sooo....maybe I have an older version of the MK3, but mine doesn't fit. See the picture for the difference. Is there a different nozzle that fits my fan? The orange one is what came with my MK3 a little less than a year ago.

Hi TheOtherVance,
This nozzle also fits your printer, but then you have to print and use the nozzle support provided.
If you do not want to use the angled nozzle I have also made a straight nozzle (Bear Nozzle) with two air ducts.

Ah, I'm a spoon. I didn't even notice the other file! Thanks for the other version as well!

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I printed this in Natureworks 3D870 PLA and annealed it by putting it in a container, pouring 90C water on it and leaving it for 5 minutes. Miniscule deformation from the annealing, but now no deflection at all, even with the bed at 120C.
Fantastic design! Much appreciated!

Slice engineering just released models of the mosquito hotend - any chance this could be modified to fit that as well? It's a bit wider than the stock e3D, so most shrouds end up hitting one side of the block and melting.


I look at it, but if I have found the right files then that design looks very different :-(

hmm, I'm using this: https://www.thingiverse.com/thing:3019150

so I thought maybe it was pretty similar since it's essentially prusa parts but remixed. I could definitely be wrong though :/

MK3 R3 mosquito mount
by zando2k

The one I found looks different.

Mosquito Hotend Slice Engineering

Prusa MK3 Mosquito Hotend Extruder

oh yeah I was gonna use that, but I went with the prusa remix in the hopes that more fan shrouds would work with it lol. But they're a bit too narrow.

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I literally just downloaded this to edit the bracket for the BMG and I find you already done it today! Cheers
This ia great performing shroud, thanks.

Would this fit on the R2 extruder head version?

Hi lordcarlos, Yes it also fits the model R2.

impression parfaite, montage sans soucis.
Merci :)

Merci beaucoup!


Do you think you can incorporate some form of 'anti-torque' mechanism?

When I tighten the screw on the PR version, the nozzle tends to turn right.

There's also a GitHub issue: https://github.com/prusa3d/Original-Prusa-i3/issues/112


If the nozzle is correctly printed and that the extruder body has no defects, the nozzle cannot rotate.
Properly mounted there is no gap between the extruder body and the nozzle. When the nozzle screw is tightened, the nozzle is pressed against the lower side of the extruder body.
Could it be that you have drilled upp the size of the nozzle mounting hole?

This is a great part. i printed it with ABS (no supports) and it works like a charm!
thanks a lot for your work

its a very nice Nozzle.
But i have a question to this.
Is "whitout Support" for the Nozzle realy right? My results are not very satisfactory.

Note: I am currently working on a lighted version of your nozzle, of course without interfering with your air management.

No, support material is not needed for the nozzle. You can print the nozzle in ABS without troublesome strings or defects.
Just keep in mind that ABS requires a little cooling for bridges to be good.
You can also use the attached configured gcode file.

Thank you for your point of view.
Nozzle support is now updated.

Revision C works really great. Perfect fit for me. Can I ask for a small change on the fan holder? Please let nuts sink in more so that a shorter screw can be used (like on the original prusa fan holder). Thank you!

Awesome design and testing images. I really like this nozzle. May I ask for the STEP file? I am making a custom extruder and I would like to incorporate this into my build. I have to modify the housing for fan attachment though.


Here they are, and good luck with your extruder.

I tip my hat to ya! Thank you. I'll tag you for sure when I mod it. Appreciate the sharing. I too always share files. Some don't and i am not sure why.

Revision C is super awesome! Much improved design - even better cooling! I posted a make in Polymaker PC-Max

Stahlfabrik, thank you very much for your nice recession. I am now beginning to believe that the air nozzle works well for an MK3 and that theory and practice seem to be well-matched.
And thank you for your support and taking the time to test the nozzle.

This printed well. I have just a couple of comments, which I will show in picturess when I post the make.

First, my fan has a rib on one side that required me to file a corresponding notch in the side of the nozzle part. My fan came with my Pruda Mk3. so I'm guessing that it's standard, but I also guess they have more than one supplier, some with & some without the notch, so I suggest add the notch to the model. I don't think it will affect anything on non-ribbed fans.

Second, I really appreciate the research and effort taken to model the airflow and to get this part designed to improve the cooling. A great job! My feedback on a test pieces made on the old & improved nozzles did not show any significant difference however, So I'm a bit disappointed, but fairly certain that it will be better on the majority of prints, and I hope there will be improved versions to follow.

I have a fairly diabolical fan arrangement that ducts air from an 8 cm computer fan onto the back of the print area. It works but I don't like using it so I hope this this research makes it redundant one day!

Hi Chattel, and thank you for your comments.

It seems that there are fans in a slightly different version. My fan also has this rib, but it is 3 mm up from the fan outlet and is therefore no problem.
I am now working with revision C of the nozzle and there I will make a track for the rib.
Revision 3 is modified inside and will have a slightly larger airflow through the front outlets. The internal geometry is also modified to reduce the risk of hanging strings.

Excellent! I look forward to trying rev C.

Is it ok to print this in PETG? Is this part exposed to higher temperatures so it needs ABS?

To the nozzle I recommend ABS or a material that can withstand higher temperatures. I have tested them in PETG, but the material is soft and the nozzle is deformed.
PETG to the nozzle support is an excellent material.

"I have tested them in PETG, but the material is soft and the nozzle is deformed."

Deformed to the point of failure? I don't have any ABS and have never printed with it, curious to know how much of an issue the deformation actually is if I printed with PETG.

Also, thank you for sharing your work to improve the Mk3.

A slight deformation has no significance. But the nozzle must not collide with the actual print.

Do you think that aiming the air higher will cool the heater block more and cause the printer to struggle at higher temperatures ?

No, the air jets are directed downwards and under both heat block and nozzle, which you can look at the images from the analysis.
So there will be no additional power load on your heat block.

You're great! I don't recognise it :-(
Perfekt fit!
One question ... what profile did you use for "MK3_ABS_Nozzle_RHD_Rev-C_0.15mm.gcode"? It works nearly perfekt with TitanX ABS Filament on my mk3.

Hi raar,
To the nozzle I use the profile for Prusa ABS. On that profile I have adjusted what is marked with yellow in the attached PDF file.

Thank you very much!
Best regards

Hi raar,
What do you think about the extruder from Bondtech? Can you see any improvement on the surface finish of what you are printing?
I am thinking of ordering one if it performs better than Prusa original.

I had some problems with the original Extruder so I changed to the 3:1 BMG. I had no direct before and after pictures but I tried now to make some pictures of my currently BMG prints. Curiously the BMG prints in 0.2 resolution are much better than before. In 0.1 are fewer differences.
Hope the pictures will help ;-)
Some explanation: The pink Phil-A-Ment is Dremel PLA at 0.1, The Prusa orange Phil-A-Ment is PETG at 0.2, the silver Benchy is Prusa PLA at 0.2 and my portrait is Prusament PLA at 0.2
What do you think about the details?

In my eyes it looks very good! No disturbing layer shifts can be seen. Could it be because Bondtech has a 3: 1 ratio of extruder feed and Prusa has 1: 1?

I think also it looks very good. Maybe some "specialists" have soemthing to gripe ;-)
I think not only the 3:1 ratio is the reason. It works also very smooth

Thanks man