Prusa i3 MK3 Alternative part cooling duct V2

by robrps Aug 23, 2018
Download All Files

Thing Apps Enabled

Please Login to Comment

I am going to use it on a custom mount I am designing, but I don't know how many distance is between the bottom of the part and the nozzle, could you please tell me?

It's designed to sit 2mm from the tip of the nozzle. On a standard E3D nozzle, that is level with the bottom of the hex part of the nozzle.

Thank you so much :)

Printed it Hatchbox Orange ABS - scaled to 101% and came out perfectly. Awesome design.

我对它做了一些修改 以适应我的热端支架

Thank you, you are welcome to use it. :)

(thanks google translate!)

Absolutely the best upgrade for the printer. It is so clever.
Would like to have it on the R4 extruder.

Quick note of thanks for this awesome design. It's well thought out, and works great.

Any chance for version for new prusa R4 extruder ?

No plans, sorry. I'm not a fan of the having the fan at an angle.

Needed for PETG printing.
With other model (tested several) regular problems of temp variations for the extruder even with a silicon protection.
Now with this design temperature drop 2°C and is quickly restored.
Thanks for this because it solved a big problems.

I'm going to print this and try it to see if it helps with the low fan speed PWM noise. I'm mostly printing PETG and am wondering if anyone's made alterations to this or knows about a fan shroud that allows 100% (quiet PWM) fan speeds for PETG... I think you'd have to essentially block airflow, or send 2/3rds of it out the back end and not towards the print? Thanks for all the hard work making this shroud and allowing us to have it robrps!

Perfect print in an hour at .2 resolution, 30% infill, red PETG. Looks and acts awesome. Thanks!

Glad you like it :)

I'm confused on which STL file I need out of the 4. I have a brand new MK3 with the angled fan

You'll need the one with the arm and the custom support. This fan is mounted without the angled bracket when using this duct, however if you prefer an angled duct, then you'd be better served with RH_Dreambox's duct - https://www.thingiverse.com/thing:3249344

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

Hey, love this desing. I really do but I cant use it anymore :( went for the BMG Extruder update and it doesnt fit anymore... only with a 45º degree angle :(

Glad you like it, but I have no immediate plans to create a BMG Extruder version because I don't have one. However RH_Dreambox has a BMG compatible version of his part cooling duct here https://www.thingiverse.com/thing:3249344 This works really well too.

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

Great fit! Looks really nice, too. With this, you cannot see the nozzle easily, which should not be a huge deal. Cooling capacity is slightly better than the r3 parts but makes the blower fan much quieter. The 45-degree angle design of the r3 made the fan whine when not at full blast, this one eliminates that.
Also, I love the return of the warning "Hot!"

That is a very fair and comprehensive review. This seems to be the best R3 duct I've used (I've tried 'several'). This Rob character has both technical savvy and design ability. He is a great asset to our community.

Is there a version that fits the Prusa i3 Bear 0.6 alpha extruder?

There is, but not tested by myself - https://github.com/gregsaun/bear_extruder_and_x_axis/issues/20#issuecomment-440711254
It's going to be probably after Christmas before I get time to print the new Bear extruder and test this fan for myself.

Any chance to get the source STEP for this? I'd like to make some small modifications to fit my hotend setup if possible =)

STEP or would your prefer the Fusion 360 file?

The Fusion360 file would be brilliant if that's ok :)

Thank you!

Fusion 360 uploaded ;)

You're a star! Thanks =)

Great work! How far are your plans regarding the 45° version? I'd really like to attach this to https://www.thingiverse.com/thing:3206085.

Prusa MK3 Bondtech bmg extruder

Going nowhere at the moment! The version I tested had worse slightly worse cooling, so I wasn't bothered as the current version worked better. But if there are other Extruder Mods for the MK3 where it required 45° then I'll look again. Realistically through, it will be after the new year before I revisit the 45° version.

Since this release, I've been working on a Bear Extruder version as that is what is I'm currently printing with.

That would be great.
Does your test-version have worse cooling compared to this improved design or compared to the Prusa stock shroud?
I mean possibly even a work in progress design here would be greatly appreciated. =^_^=

It was performing about the same as the stock R3 duct. I scrapped the model sorry.

Ah well, it was worth the question.

I don't have it yet - but any idea if this would fit around the mosquito hotend when using the extruder body here:


Someone mentioned the stock shroud would clip the heater block and melt, so I'm curious if this one was any "wider" than the stock shroud?


MK3 R3 mosquito mount
by zando2k

just an update - unfortunately it does clip the hotend.

That's a shame, thanks for testing it though.

Comments deleted.

Thanks Rob for this design! Your custom support version printed on MK3 R3 Bear eSun PETG without issues. Cheers! EDIT: oops I did have to do the 0.44 thing due to chunk missing in Slic3r, as discussed below. Thanks Tony for catching the Slic3r glitch!

I tried to slice it in Slic3r Prusa Edition and I get a missing part. Screenshot attached.

That appears to be a bug in Slic3r PE, it wasn't doing that when I last printed it! The other side slices just fine and that is the same line width... A quick fix for you is to change the 'External Permeters' to 0.44mm, it should slice fine with the current version on Slic3r PE.

Thanks for the quick reply. Print aborted. I'll try your fix.


Thank you. This fixed it.

Are you going to update the file for R3 parts?

I have been using this on the R3 parts for a few months now. it is interchangeable.

Even tho the fan isn't at 45°?

This fan duct performs better than the prusa stock duct at 45 degrees.

I've always had problems with cooling "behind" the nozzle. There are two Adalindas on the attached photo, printed with their wings facing back, so the rear edges of the wings are in the problematic cooling sector. I see a clear improvement with this shroud, well done!

Thanks for your comment and make, I'm pleased its working well for other people :)

Any thoughts on making it fit 2 fans, either vertical or angled, just for grins?

I've seen them, but I've no plans to make a version as yet. I want to first make a tweaked version of this for the Bear Extruder, then I'll see if I want to do a dual blower version. I don't really like the way the end up looking tbh.

Is this latest version Bear compatible?

There is a specific Bear version for the current Bear extruder (0.5) which can be downloaded from the link below. I'm not publishing it just yet, as there is an update to the Bear extruder which will prevent that file from fitting properly.


This looks awesome, and I'm anxious to try it! One question... Any chance that you could make an extension that lowers it a bit to use with a Volcano? Thanks!

I hadn't intended too as I don't have need of a Volcano. Is there a standard extruder body for the Prusa MK3 for use with a Volcano?

Nah. It's just their standard body. I was hoping for a fan mount that was lower, but it looks like I'm gonna have to modify the extruder itself. Thanks for the reply!

this thing has made my PETG bridging so much better. works with the r3 parts fine. I did the duct with an arm so the fan was nice and solid but even that is probably not critical.

Glad you like it.

Great cooler duct, I have been using it successfully since the day you released. I printed in ABS and it turned out perfect the first print using the "generic abs" filament profile in slicer. My question is, will this duct work with the new Prusa R3 extruder configuration Fan mount? I did not print the new R3 parts yet mainly bc of this, and the extruder disassembly.

I got bored of the F1 today, so I put on the R3 parts - they are compatible, as long as you don't use the 45° bracket.

I did reply to this, but it's under moderation for something. I don't know yet if this works with the new Prusa R3 extruder cover as yet, but I will be looking to see if this can be mounted as is (albeit with a screw hole missing for the blower), I'll also be looking at updating/adding a version of this duct with a 45° entrance but that'll take a bit of time. I need a new extruder motor as I've damage one of the cables where it goes into the motor. When the replacement arrives I'll stick on the R3 parts and this duct to test.

I have got a minor update for this which beefs up the screw block and adds a small amount of adjustment to lower the duct if needed. This should go up today.

I will check that out when you release it. I did upgrade to the new parts today and the fan and blower fit perfectly!
Prusa made it backward compatible. thanks for verifying.

Thanks TheNore - I will be looking at the R3 design and plan on adding a 45° version of this that using the same mount as R3, unless that is not feasible. This weekend I'll be strengthening the screw block and changing the hole to a slot to allow for adjustment to lower the fan duct a touch as per the comments below. That might end up being a separate STL.

I've mounted mine on the Bear Extruder, but I'm putting back on the R3 extruder to check the height against the nozzle. My extruder motor is play up, so I also need to get a new one....It's a good job work for a company with lots of different printers.


Thanks for the excellent design!

I can't however notice any difference between the stock cooler and your improved design. I tried printing the overhang with the stock cooler and with the improved design, with no noticable difference (see the attached file, the stock print was aborted because I thought it was going to fail completely).

I printed the overhang with 0.2 mm resolution, 20 % infill. Any special settings I should be made aware of?

Many thanks.

Hi Sebgus,
You should be seeing a lot better than that - have you also tried the new Prusa R3 duct? I'd be interested to see if you get better or similar results.

If possible, can you see if the exits on my duct are not too high up? Does it look like its sitting in the same position as the photos with the red duct. I am wondering if there is a need to add a small height adjustment on the screw block to let you adjust the duct to a lower position.

As for setting,assuming that you are printing in PLA - 100% fan (obviously!) and check you are not printing too hot. I find that there is a sweet spot for most PLA where it looks shiny when printed hot, and matte when printed cold. The sweet spot I find is at that transition, I prefer the shiny side). Printing fast can also make PLA matte looking, like the infill at 200mm/s :)

edit: One thing else too check - are the duct clear, i.e. has the bridging roof printed OK?

Hi again,

A short update. The fan looks fine inside, water runs fine through each path. I also did a test with having a bowl of water underneath the extruder (see attachment). Looks fine there as well.

I will try your new design as soon as it's up. :)

Hi robrps,

Thanks for the quick reply. I haven't installed the R3 duct. I didn't want to tear apart the whole extruder since it mostly prints fine as it is now.

It could be that the exits are a bit high up (see attached image). Either an adjustment screw or maybe angle the exits slightly?

Yes, I'm printing PLA. I did a temperature tower and didn't see that much of a difference between 210 and 230 degrees (printing with the Prusa Black PLA filament, right now at 215 degrees).

The duct seemed clear after print. I could try running some water through it just to double check.

I've been trying to improve the cooling on my Prusa MK3 for some time. The height of this duct has to be adjusted properly, as it seems to rely on pinpoint accurate cooling for maximum efficiency. I think it has to be installed as high as it will go. The first time I installed it, it performed slightly better than the R3 duct. After reinstalling it, however, it did not perform well at all, I am trying to rediscover the sweet spot...

Hi, I'm having difficulty getting Slic3r to properly load this model. In the segment that is next to the Pinda Probe, gaps are appearing in the model and I can't seem to get rid of it. The setting that seems to affect it is the perimeter width. I have mine set at .45mm, but I have tried .4mm to .5mm and it only changes where the gaps appear, but doesn't eliminate them.

I'm also having some bridging problems where the channels meet the opening where the air comes down from the fan. The printer is creating the perimeters for the fan opening, but where the bridging is trying to link up to those perimeters, it's collapsing. I'm trying to adjust some settings to try and correct for this, but it seems to be a troublesome area. I suspect the problem is because the perimeter isn't bridging as a straight line over the gap, so the reduced extrusion is pulling it away from where the coding is expecting it to be, so the ends of the bridge aren't connecting up to it.

Ah, yes. I forgot to add that in my Slic3r setting I've got the external perimeters set to 0.4mm, which is enough to close that particular troublesome spot with one outer and one inner. (see attached). I'll add that to the print settings. Thin walls turned off too.

I'll also add my gcode from Slic3r to download, you can either print using that, or File -> Load Config and use my setting but change your filament setting. The gcode was printed using Extrudr MF-PETG.

As for the bridging I assume that you mean the roof of the ducts? Look at altering your bridging angle or rotating the part. Try my gcode, it worked for me, but I was using another fan duct to print it (the R3 Prusa angled fan) which is better than the previous stock duct. If that doesn't work, let me know and I'll see about adding another version with some uprights in the ducting to help with bridging.

Ok, so I got a good final print after a few attempts. The first one was no good cause part of the bridge collapsed and blocked the airflow. After some adjustments and looking at your config, I got one to print out better, but still had some partial collapsing of the bridging. But it was usable to switch out from the Stock duct.

Using the new duct, and changing the bridge direction (direction perpendicular to the HOT! wall), it printed much better and it didn't collapse.