Prusa MK3s/2.5s/MMU2s Mosquito Hotend Extruder

by stegenga Mar 25, 2019
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Love the design I've had great luck with it! I was curious however what settings youre using for your MMU2S unloads? I can't for the life of me get the tips to actually work. They always come out as balls. Any help would be much appreciated!

My filament changes having been going pretty good with default settings except for PETG White filament which does blob and clog at times. I am trying to find to time to work on it using the settings in the slicer but other home projects keep getting elevated above this. When I do I will be looking at the slicer section below to try to resolve:

It's strange but after changing I have also to change the E Steps in the firmware. Did someone had the same problem?

Instead of 100mm filament it extrudes only 94mm

I leave the E Steps as-is (Prusa recommendation) Based on my experience with different materials, their density, pigments and tolerances, I have been able to adjust flow rate using the slicer and/or printer menu options to get the best quality while visually checking the result. Mathematically, 1.75 filament with a +/-.05 tolerance already yields a possibility of >10% variance in material flow. So I let my eyes do the calibration on this one.

Hi, What is the extInsert part for?

Prusa's extruder housing has three parts labeled, Body - Motor Plate - Cover. I use Body - Insert - Cover, mainly for brevity. So the ExtInsert is the extruder-motor-plate.

have you tried TPU on the mosquito? I get great results on my mk3s with sainsmart but lately I'm getting constant jams and looking to upgrade to the mosquito with the new bondtech kit. thanks!

No. Just PETG and, rarely, PLA. Maybe someone else viewing here who does can respond.

Thanks for the model!
One issue, the latest mk3s extruder cover is different, and my dual part-fan doesn't fit.

Printed as is for test, now trying to merge it with Nimble extruder model and replace the extruder cover with newer one.

I'm assuming you glue the PTFE in to the t-mount?

No. There is a small lip at the top of the tube path that holds it in place. You just need to external bevel the bottom, cut to size to the lip, and internal bevel the top. I bevel the bottom by rolling it in a piece of sand paper and bevel the top by twisting the point of an exacto knife.

That's fantastic! Thank you for that. Ou of curiosity, how often does the mosquito magnum clog and require PTFE change overs?

Hey, The fan shroud will not fit unless I cut away quite a bit of the plastic. Then I imagine the air wont flow as it's designed to.

This is the piece Vlaidin is referring to. Just grab the center with a needle nose plier and it should 'snap' right out.

You're supposed to remove that bit of plastic, it's there for support while printing.

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Thanks for your model! I printed it and it is working fine with a Mosquito Magnum with the following changes:

  • I had to modify the firmware to reduce the length used to test the filament load - it was getting into the melting zone.
  • I had to print the fan shroud in ABS - with PETG it was deforming when printing at 250 °C.

do you have magnum or std?

Mosquito Magnum

Thank you very much for the models. I was having trouble with the fan shroud cooling off the heater block to much so I took it off. Hopefully that's a good option.

As 'they' say here in the US, "It depends."

First of all, the fan shroud is Prusa's latest design and, I agree, it is not optimal. They put a slanted piece at the main output to direct the flow of air down towards the nozzle. Being a racing sailor and knowing a little about air dynamics I can't help but believe that there is a little backwash up to the heat block.

That being said, one of the main reasons for cooling the filament as it comes out of the nozzle is for bridges. My designs either incorporate small bridges or I design removable supports into the piece. Actually very similar to what Prusa did with the part fan shroud and what I did with the mounting holes in my T-Mount part. I also print in PETG exclusively and I find it more forgiving to printing without the part fan running.

Anyway, just some observations with the key one being, if it works for you then just enjoy.

I've had to cut away quite a lot of the material to make the fan shroud fit, so the less than perfect air flow is going to be even worse now. Not sure I should even print with it like that. I really don't get what could be wrong with the shroud, I didn't personally print it but, it's just been printed from the files here. Any ideas?

Do I need the 12v fan or 24v fan for the MK3s? Thanks

Neither. Prusa's MK3(s) stock noctua fan is 5v. So I just use the existing fan and connection as it has RPM managment.

For those reading this that have an MK2(.5)(s), that uses a 12v fan so you can use the Mosquito 12v or the stock fan. Again, I use the stock.

Where did you get the Slice Wheel from? I can’t seem to find it.

I designed it myself for personal use (and a practical MMU2s test) and did not post due to copyrighted logo. I have since talked with the Slice Engineering owners and they have given me written permission to publish it for non-commercial use once I redesign it using their official .ai graphic and specific font. I will add a reply here and a link when that is done for those interested.

Nice. I liked the look of it!

Did you release it yet?

I just published it tonight. I had run out of white filament.

It is at: https://www.thingiverse.com/thing:3724481

Slice Engineering Extruder 'Windmill'

I do not see any mounting bracket for the top screw on the parts fan just under the motor. Am I missing something?

No, you are not missing anything. Use the stock Prusa part. I only put the modified parts here. While the mount point of that part changed, the part itself did not.

So I ordered a Mosquito Hotend for my MK3S. Since getting a Palette 2 Pro I have been getting clogs/jams constantly in the PTFE tube about midway in tube. I hope this new hotend will help with this.

So since I will be tearing down my MK3S when parts come which is best to use the stock fan or the new 25mm? Also didn't see cutting guide for PTFE tube. 40mm?

Any suggestions would be GREAT!

The Prusa stock fan is three wire with power management and quiet. The Mosquito stock fan is two wire and you will hear it. I use the Prusa. (Edit: I was referring to the MK3 fan. The Prusa MK2-2.5 series uses a two wire fan)

The cutting 'guide' is the picture plus description to have it seat against the mosquito on the bottom and the 'lip' I created on the top. Beveling the bottom on the outside to fit snugly into the mosquito and beveling the top on the inside for better filament entry.

Thanks for the design! I swapped it in during my MK3 to MK3S upgrade and it's been working like a dream so far.

One thing that I did notice is that my prints were much stringier after the upgrade. Bumping retraction from the default 0.8mm to 1.5mm completely resolved this, even making it better than stock in some cases (such as with PETG). This is using the standard Mosquito with the 0.4mm Vanadium nozzle.

Sorry for the late response and thank you for the tip. I have been away for over a month setting up a sailing program for a summer kids camp in the north woods of the US and had no access to internet/cell.


have you tried printing with TPU/Flex?

I installed it and love the hot end - and works like a charm with PLA/PET/ABS (and other rigid exotics)

But TPU/Flex material gets wrinkled and jams due to shorter tube and the space between the tube and the gears..

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Thank you for this design! Everything prints well!
One thing i noticed is that the print fan shroud isn't centered on the nozzle, its offset a couple mm. I lack the skills in Fusion to modify the shroud and correct the offset.
I've attached a picture of what i'm seeing.

Which way is your mosquito mounted? I designed the mount with the cables going down the side closest to the home state. In other words on the Left side as you look at the printer from the front as in my pictures/videos. Mosquito logo is facing out but that can be reversed. Maybe when I get a moment I can design two versions. One for left cabling and one for right. Since the mosquito heat block is asymmetrical.

Thanks for the reply!
It's mounted with the Mosquito logo facing the front of the printer, and the heater & thermistor are on the left side. I almost tore it apart to flip it around then i realized that wouldn't do any good. The filament path is aligned with the nozzle and the middle of the heatsink like in this attached picture.

Edit: When i get home tonight i'll verify that i printed the R5 fan shroud

...and you printed the fan nozzle/shroud that is part of this thing? Prusa"s is too narrow. If so, I will check to make sure I posted the correct shroud file

I looked at the thing i downloaded originally, i must have downloaded it right before your recent update. The part cooling fan i printed was called FanShroudXL.stl. I'm going to reprint with the FanShroudR5.stl and see if everything lines up

Edit: I printed out new FanShroudR5.stl shrouds and it's still offset. Here is a pic from underneath. The top of the pic is towards the front of the printer.

Mine is offset, too. I have the FanShroudR5.stl, and the hotend is mounted with the mosquito logo facing forward.

If by 'offset' yours is like Vlaidin's picture then that is the design. It is the heat block that limits the design here as the nozzle is offset on the block in this positioning. In order to be aligned equidistant to the nozzle the fan shroud would need to come from the side. It is on my list to look at designing a new shroud for this but the proximity of the PINDA prohibits me from mounting the Mosuito in reverse (too much heat at PINDA) and mounting the fan and shround on the right would block the heat break cooling flow as well as take that already hot air and flow it to the nozzle. Any and all suggestions are welcome as to how best rectify this.

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Sorry Vlaidin I was mistaken so I have deleted my previous comment.

Does this extruder work on the Bear X axis?

You would have to check with the owner of the Bear if they use Prusa stock mount for the newer 's' series. My mod mounts using the stock Prusa X-axis which, on the newer 's' parts, uses the two upper motor screws from the back, and (new) two screws from the front on either side of the hotend.

I love the designs but do you think you could make a version of the 2.5s, 3 and 3s mount to fit a BMG M and mosquito?

I do not have access to a BMG M to design. I have looked online and can not find a STEP, STL or other CAD object of the BMG M I could use. I assume that since mounts for the Mosquito to the BMG already exist, you are looking for something more 'complete' with Pinda, sensor, and fans mountings, etc. to mirror Prusa's stock configuration. Sort of like this, https://www.thingiverse.com/thing:3245861 , but for the Mosquito and the newer Prusa 's' parts. If I had a file or the BMG M, I could possible design.

BMG Extruder Carriege for Prusa i3 MK3 Short and Bearing Version
by drodfro

Does this affect the maximum print height at all?

No. In order to avoid any firmware or default slicer profile changes this installs in the same space of the E3Dv6. In reality, the Mosquito is approximately 20mm shorter and I could design a smaller extruder that would gain 20mm in printheigth capability but that would mean user software modifications. I am planning to 'play' with it later in life :-)

Ah, I thought the Mosquito was taller so I was worried it would lose Z-height. Glad to hear that's not an issue.


Is there an assembly guide for this? Maybe a video?

It is all in the description. Use these parts and instructions along with Prusa's official documents.

It is n't as easy to follow for me. lol. Also how do you prefer the orientation for printing?

Great design I printed it out and fit it together like it was supposed to be I just have to go back and check pinda and z calibration but if it matches stock specs it should be straight forward and also what slicing software do you use? But overall you made that simple

I've been having a few issues with my filament getting caught around the gears is there a setting I can do to fix this. Does anyone else have the issue? My prints come out like this

I use the Prusa provided Slic3rPE. It gives me all the controls I need for my MK2.5s/MMU2s and MK3/MMU2 with PETG filaments and the Mosquito hotend.

Note: I will be updating the extruder cover and fan shroud files this weekend as I just completed testing for the MMU2s and had to make some 'adjustments' to make these parts universal in the new Prusa 's' series. It is an easy replacement if you already have the extruder installed, just the front fan screws, the two cover screws, and the fan angle bracket screw will need to be accessed. Details as to why when I post it and you can decide if you need it.

Was wondering if you have updated the files? I have the mmu to make sure that this will work with the mmu. thanks

What other parts, or hardware is needed to use this, and move over to this extruder on the Prusa MK3 besides what comes in the box?

Please read the description. It is all there.

Any chance of a pre-sliced version? For printing on our MK3s?

gcode versions are very dependent on your environment (Extruder, nozzle, print bed, filament type/color, etc...) I know Prusa provides gcode for their self-printing upgrade parts but that is also because they provide you with their black PETG filament and 'assume' you are using their stock printer config. My slicer profiles are well beyond that and anything I slice would probably be of little use to anyone else. Sorry.

This is great! Any firmware changes required? Or do measurements match stock?

No firmware changes. Nozzle and PINDA positions are stock as is vertical distance of filament path.

Would this work with the MMU2?

I am testing with the MMU2s right now. So far so good. I will update the header and description once I have verified it.

Any update on this? Still working good?

Yes. MMU2s on MK2.5s worked great. I am still waiting for my 'free' upgrade on my MK3 w/MMU2 to test it in MK3s/MMU2s environment although I expect no problems as the extruder parts are the same.

This is odd, but is the fan duct useable by itself on the stock extruder? I have a oddly shaped copper heatblock and the stock cooler won't fit the thing.

Yes, ...and no. This fan duct will mount on the Prusa stock extruder cover using the capture nut and the front lower fan screw as designed. HOWEVER... while no modifications were made to the duct mount, the part fan mount to the cover has been altered.

  • I split the stock Prusa fan duct and added 4 mm in width
  • That additional 4 mm gap is added to the left side and the part fan opening is shifted left to compensate
  • While the top part fan mount screw remains the same, the lower arm is shortened to line up with the shift

So, you have two choices if you want to try it:

  • Use it with the stock Prusa cover and just use the top crew for mounting (which is more than secure IMHO)
  • Use my cover but note that the extruder cooling channel will be slightly different and may affect efficiency (No Guarantees)

But I would take some measurements first to see if the gap will work around your heat block. In other words, is the right side of the duct okay with your block and just moving the left 4 mm will work? ..or do you need to have both sides move out which this will not do.

Well, thank you for all the info, In the end I was I just went back to the stock block, copper was interesting, but for some reason I could never get good thermals with it.

Regardless I am thankful for the info.. I did however, also change to a more rounded front and sides directed cooler after changing back.
Your design work on editing this all looks very good.

Lastly, I realise this post is very late. And wanted to say it's likely this could of fit, I had the block mountted such that I needed more room in front, and really needed cooling coming down from the sides only to not blow on the heater block!

Thank you for your work. Will try to print out shortly. I guess you use all the other Prusa R4 parts where the magnets and steel ball go?

Yes. I only had to mod the lower parts of the extruder body/motor plate/cover and widen the part fan nozzle. FS parts, top plate, idler and x-carriage parts are Prusa. Make sure to use new T-Mount for Mosquito as I had to modify for three part vs. two part extruder.

? What do you mean use new t mount?

Some people. like me, may have already installed the Mosquito using my other mounts for Prusa's two piece extruder body. If so, they need to remove the previous T-mount and print and install the one here for the three piece extruder body as it has changed.