Building the Prusa i3 MK3

My previous experience putting together 3D printer kits has included splicing wire, soldering, adjusting potentiometers, cutting and drilling parts, and even building small circuit boards.

The Prusa i3 MK3 kit suffers from none of the above. It is a well designed kit that I would compare to building a complex lego set. This is helped by a detailed manual (both printed and digital), properly labeled bags, community discussion, videos, and hundreds of hours of testing.

If you are confident you can properly connect negative and positive wires to the correct terminals and follow a visual guide showing you where and how to connect pre-made wires, then recheck everything, I believe this kit isn’t as hard as it might seem on the surface. With a few tips I think most people, who can handle the above, can easily put together the i3 MK3 kit.


  • Expect to spend 4-8 hours building the kit.
  • Always read the instructions first before starting. They often include important build instructions that help you understand why you are performing the tasks.
  • I highly recommend using a torque controlled screw driver designed for electronics/delicate-parts and set it to the lowest torque setting. Allen keys are too easy to over tighten and you can end up with cracked parts. I know this is an added expense, but that tool will come in handy in the future so it is not a lost investment.
  • Before you let loose with the power screw driver or even the Allen keys I would hand start any screws to make sure they catch appropriately. This will prevent binding and stripping of threads.
  • Triple check the power supply and bed wires. One of the few things that cannot be fixed is powering up the printer with it incorrectly wired for power.
  • The P.I.N.D.A. probe should be very close to the surface of the print bed while the nozzle is touching. Setting the P.I.N.D.A. too high will result in the nozzle possibly crashing into the bed. The manual recommends using the thick part of the zip tie, however I used the thiner part of the zip tie instead based on my experience with the P.I.N.D.A. probe on the Prusa i3 Mk2.
  • Use the online manual if the print manual images are not clear. I found this particularly helpful for the E Axis and E Axis wire strain relief.
  • A majority of screws and parts are color coded in the manual. The manual will show, for example, a screw boxed in orange then often an orange arrow or box where the screw goes and finally an orange bullet marking in the text that refers to this part and screw.


Aside from using the occasional wrong screw I did run into two significant issues that you might be able to avoid.

In the right Z part you need to insert a nut into a hard-to-access slot. Unlike other places in the manual where you can essentially pre-seat the nut, this is not possible (see the blue box below).

Right Z nut placement

When trying to insert the screw it ended up binding and I was not able to either reverse the screw or tighten it. The nut would spin and even with significant force trying to hold the screw in place I could not dislodge the two. I did this without the trapezoidal nut installed because I was trying to align the nut and screw. The trapezoidal nut cannot be attached due to the screw head. The solution, for me, was to cut the screw head off:

Z nut fix

The printer works in this setup, however I will print a replacement right Z part to have the trapezoidal nut properly secured.

The second issue I had involved the calibration wizard. I was getting self test error “X-Axis Length” which essentially means the printer is not returning the expected length of the X axis. Often wires or zip ties can cause this, but in my case the Z was misaligned enough that there was minimal binding stopping the X from moving the full distance. To solve this you can exit the setup wizard do a quick Z calibration. Once that was done the self tests all passed in the wizard.

I hope to put up a review of the Prusa i3 MK3 in the next month or so.

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