Extruder for Prusa i3 MK3S

Extruder with Mosquito hotend for the original Prusa i3 MK3S

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I wanted to upgrade my Prusa i3 MK3S with a Mosquito hotend, so I decided to design a new extruder.

On the homepage of Slice Engineering [0], the manufacturer of the Mosquito hotend, I followed a link to a modified extruder for the Prusa i3 MK3S [1].

I had a quick look at it, but decided to improve my designing skills by creating a new extruder.

In order to use the stock firmware from Prusa and to keep as much stock parts as possible, I had to consider some geometric constraints:

  1. Pattern of the mounting holes
  2. Keeping the position of the nozzle (X-,Y- and Z-coordinates relative to the carriage)
  3. Position of the P.I.N.D.A. Probe relative to the nozzle-tip
  4. Mounting holes for the hotend fan
  5. Max. overall dimensions of the extruder

As a base for the new extruder I used the model provided by Prusa [2].

First I removed the lower half of the model, placed the Mosquito hotend and rebuild the lower half around the hotend.

Mounting the hotend

The hotend is held in place by a form-fitting cavity, so there is no need for a mounting bracket or something like that. Most of the required pressure is applied in the upper part of the heatsink, so I am not afraid to deform the U-shaped heatsink accidentally.

Air ducts

The air duct contains guides for the airflow. The guide in the inlet should guide a part of the airflow directly to the little heatsink on the heatbrake. To prevent the deforming or melting of the extruder, there is another guide in the outlet. It should guide a small amout of air to the plastic part of the extruder which is very close to the heating block.

I am not an expert in CFD-simulation. If you have any idea how to improve the duct, do not hesitate to contact me.

Filament guide

To guide the filament into the hotend I used PTFE tubing. The tubing is held in place by three little "teeth".

Optional temperature sensing

At the rear of the extruder you can attach a temperature sensor to the heatsink of the hotend. I added this feature to check the function of the air-cooling. On the picture you can see some white rubber foam which is used to press a type-K thermocouple to the surface of the heatsink. This is not suitable for precise measurements, but it will indicate if your extruder is going to melt.





Standard Tesselated Geometry - 2.87 MB - 09/19/2019 at 17:24


Standard Tesselated Geometry - 904.77 kB - 09/19/2019 at 17:23


Standard Tesselated Geometry - 379.09 kB - 09/19/2019 at 17:23


Standard Tesselated Geometry - 922.35 kB - 09/19/2019 at 17:23



all models are licensed under GNU General Public License v2.0

license - 17.62 kB - 09/19/2019 at 17:23


  • 1 × Mosquito hotend
  • 1 × Original Prusa i3 Mk3S extruder for salvaging components
  • 1 × PTFE bowden tubing

  • Drawing a conclusion after ~200 operating hours

    Cadmium09/20/2019 at 08:39 0 comments

    tl;dr: I like the mosquito hotend


    I purchased the Mosquito hotend because I often had issues with heat creep during prints with PLA. In the last 200h I had not a single issue with heat creep.

    I was a bit concerned about the mechanical properties of my extruder body (PETG) during prints at temperatures around 240°C with closed printer housing. The temperature of the heatsink can rise up close to the glass transition temperature of the PETG. 

    By now, nothing happened. The hotend still sits firmly inside the extruder body. 

    Print quality

    I could not see any difference in printing quality compared to the stock hotend (E3D v6).

    tbd: It should be possible to print models with a very fine resolution in Z-axis without the risk of heat creep (increasing the resolution = decreasing the volumetric flow rate) 


    When I tried to play around with wood filled PLA, once it resulted in a clogged nozzle. Because I did not recognized it directly, the filament was grinded by the hobbed gears, so I could not remove the filament by the unload function of the printer. 

    To remove the remaining filament I just removed the nozzle (with one hand) used new filament to push the remaining filament through the hotend and screwed in a new nozzle (with one hand). 


    Compared to the stock hotend, it is very easy... almost fun.


    I have considered to buy the Mosquito hotend for a long time. Finally I bought it and I do not regret it. I had to pay a lot of money for the hotend, but it is worth every € I spend. 

    I am also happy, that I could improve my designing skills during this project. 

  • First check of the cooling performance

    Cadmium09/20/2019 at 08:27 1 comment

    I made some quick measurements to check if the cooling of the hotend is working properly.

    The measurements were made during a long print with PETG when the temperatures were in a steady state. The thermocouple for measuring the heatsink-temperature was attached close to the lower edge of the heatsink, where you can expect the highest temperature.   

    First I made a measurement at room temperature, then I closed the heated housing of my printer and made measurements at elevated temperature.

    Please note: Month ago I replaced the Noctua printer by a Sunon MF40100V1-G99-A for better cooling performance.

    Ambient temperature [°C]Hotend temperature [°C]Heatsink Temperature [°C]
    25240approx. 30
    45240approx. 60


    The thermal contact between the thermocouple and the heatsink is far away from perfect, thus the real temperature of the heatsink will be slightly higher than the measured temperature.

    As expected, the cooling at room temperature works better than the cooling at high temperatures.

    Because the extruderbody is made from PETG (continuous operating temperature ~65°C), I would not recommend to print large parts with hotend temperatures above 240°C with closed printer enclosure.

View all 2 project logs

  • 1
    Print the plastic parts

    I used the Prusa i3 Mk2.5 to print the parts. Your Mosquito hotend should fit into the hotend with barely noticeable clearance. If it feels loose or too tight, adjust the Extrusion multiplier.

  • 2
    Prepare the PTFE bowden tubing

    It is necessary to cut some kerfs, corresponding to the teeth on the extruder body. I made a 3D model for a gage to make the cutting easy.

    With FDM printing the hole for the tubing inside the extruder body will not be perfectly round. If you put the parts together and see a gap between the extruder body and the motor plate, it will be necessary to flatten the tube with a sharp knife (result is shown in the next picture).

  • 3
    Assemble the motor, gears and filament sensor

    Just follow the printer handbook.

View all 5 instructions

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