Prusa MK3.9 Review

October 13, 2023

I have a 3D printer since 2020, but I have not extensively used it. I also do not follow and know much about the technical developments in the industry. This is just a review from a user point of view. I am not affiliated with Prusa Research and this post is not sponsored by them or anyone else.

This is a short post about Prusa MK3.9 3D Printer. MK3.9 is only possible with an upgrade from MK3/S/+. If you buy a new printer, it will be MK4. However, they are very similar, and they can be considered the same for this post. MK4 has more precise motors to eliminate vertical fine artifacts (VFA).

I first purchased a non-Prusa 3D printer in 2020, but I returned it within a month and purchased a Prusa i3 MK3S Kit. It is both fun and a good learning experience to build a 3D printer from a kit. Later, I upgraded this model to MK3S+.

MK3S+ was a very good printer. There was a few issues for me.

  • it had no network connectivity, but this could be overcome easily by using awesome OctoPrint.
  • the first layer calibration had to be done manually. This is important for the print quality, however, because it is a manual process, I never liked it.
  • I have tried to change the nozzle only once and it did not go well and I had to re-assembly the extruder. The cables of extruder was a bit messy, different parts had different cables going to the mainboard.

Prusa Research says MK4 has the following features and I write my comments below for each feature.

  • High-speed printing with ease

It definitely prints faster and also more quiet. I cannot comment how fast or how quiet but it definitely is, this can be easily felt after a few prints. After I have upgraded to MK3.9, I have printed so many things in a few days, I think it is definitely much faster.

  • Perfect First Layer Out of the Box

Because it has an integrated loadcell, MK4 can automatically adjust the nozzle height thus there is no concept of manual first layer calibration. It functions very well. I have printed a first layer calibration model and it is much better than anything I saw before on my MK3S+ with manual calibration. The only problem until getting used to it is for loadcell to work properly, the nozzle has to be clean, and there is an automatic nozzle cleaning procedure before a print. This procedure is not perfect (and cannot be perfect I think without some manual intervention time to time), so you basically need to keep the nozzle clean as much as you can. This is not difficult. I definitely prefer and like automatic calibration with loadcell. I find the print quality much better than my MK3S+ before, I think it is partly, maybe mostly, because of this.

Not sure if it is only related to this feature, but also now the probe points cover only the area of the print not the whole bed, and it does not print a skirt around the print.

  • The Nextruder with Breakout Board

The extruder is called Nextuder now and it includes a breakout board so it is easier to replace a part in the extruder. There is a special, multi wire cable connecting the breakout board to the mainboard which does not require any modification if something is replaced in the extruder. In addition to the breakout board, there is a planetary gear system. I cannot say exactly what it improves but I never had any issue with filament feeding.

  • 32-bit xBuddy Mainboard

The mainboard is upgraded to an 32-bit microcontroller (STM32). It supports 100 Mbit/s ethernet (no 1Gb/s) as well as an external Wi-Fi adapter. A Wi-Fi adapter is also bundled with the upgrade and it works but I find it unstable when large gcodes are uploaded, so I am using the ethernet. However, there is a speed problem with ethernet at the moment. It is not because of 100 Mbit/s, if it works at maximum speed, this should be around 10MB/s and even a large gcode file should be uploaded in a few seconds. However, it is working much slower than this. I do not know the reason yet, it should be a firmware issue, I hope it gets better in the future. This is the only major issue I find in the printer.

  • Exceptional Print Quality

This is about precise motors of MK4 and thicker 10mm rods on Z-axis. Because I have upgraded to MK3.9, I do not have precise motors, so I cannot comment about that. However, I do like the use of 10mm rods and the new design of the plastic parts connecting the rods to the frame etc.

  • Color LCD screen and simple UI

LCD is much better. Because it is quite large now, multiple information can be observed at the same time. After the upgrade, I had a problem with LCD, it was showing strange colors, sometimes going black etc. After chatting with Prusa support, it is decided that my LCD is faulty, and they have sent me a replacement and it works now without any problem.

The LCD also has a USB (A) port for a USB memory stick.

  • Quick-Swap Nozzles

I did not try to swap a nozzle yet, but it looks pretty simple now and not error-prone. It is more expensive, but I guess for a rarely changed part it is OK.

  • Prusa Connect and Connectivity Options

Because the mainboard is powerful now, it can run better software. I am not using the cloud based Pruse Connect but locally running Prusa Link. It is much simpler than OctoPrint but I actually do not need extra features of OctoPrint so it works for me fine. The only problem is, as I mentioned before, the network upload speed is much lower than using OctoPrint (which was running on a Raspberry Pi). It is also not possible to connect a webcam directly, but I am using a network camera so it is also not a problem for me.

To sum up; print speed, low noise, automatic first layer calibration, better extruder, 32-bit mainboard, large LCD and quick-swap nozzles are all major improvements and upgrade to MK3.9 or MK4 is definitely a must. I hope the network upload speed is improved in the future with firmware upgrades. I believe OctoPrint does not fully support MK4 yet, so if you want to use it, you have to check what is supported and what is not.

If you plan to buy an MK3.9 or MK4 upgrade kit for MK3/S/+, I recommend you to check the X and Y rods first. If there is any damage, it might be a good idea to replace them and possibly also replace the LM8UU bearings for X and Y axis. Because Z rods are different (10mm) now, you will receive new ones with the upgrade kit and also new LM10LUU bearings for the Z axis.