Building a Prusa i3 MK2S

A friend needed a 3D printer for a project and I recommended him an MK2S as he was in a hurry. Printer took three days to get here and after the holidays we had to build it yesterday, but the flu forced me to delay that.

The good thing about doing yet another build is that I am quite familiar with the design and the kit, and the problem is that I am quite familiar with the design and the kit too. The latter makes you skip steps and/or fast forward into the build so you have to stop, go back to where I messed up, follow the instructions to the letter and get back on track.

Even funnier [so to speak] is when you know something is important no to skip (like which side should be up on the Y-carriage) and still missing the point: I knew it was important to make sure to identify the side with the mark. The picture showed the mark upward. Next picture detailed where the first linear bearing should be placed on, so just went on with the instructions, assuming the mark should be up while doing the assembly. Once it became obvious I have missed the point many steps forwards, I went back to realize the second picture had some text stating the mark should be facing the table while placing the bearings on top of the Y-carriage part :-(

All in all, I made just a few of these silly mistakes but the printer was built and up and running over the morning. A small test vase was half-printed during the afternoon and a fifty-hour long part is now being printed after all seemed ok.

I have found the MK2S build much improved in terms of cable handling and RAMBo-cover. Extruder part requires you keep your alert as there many details you need to do right (many different screw sizes and captured nuts). I guess instructions have been improved too. The new way of supporting the linear bearings to the Y-carriage is great but tightening the lock-nuts with the needle-nose pliers is a bit of a pain, unfortunately, I had to use just that.

Recollecting the mistakes I made along the build:

  1. I press-fit the smooth rods too early on Y-axis
  2. Placing Y-carriage upside down
  3. Tightening Y-motor before passing Y-axis end-stop cable first
  4. Tightening X-axis pulley the right distance to the motor but upside down
  5. Starting to place the extruder tensioning screws before placing the idler first
  6. Not noticing the colored measurements for the front and rear plastic parts of Y-axis
I made an operator's error while XYZ calibration was taking place: I attempted to place the spool holder parts on the top of the frame. These new holder parts are injection molded and too tight, so there was no I way I could fit them, and while I tried I caused an error on the calibration process than once repeated ended up uneventful. So the moral here is twofold: on one hand, let the calibration do its magic with being disturbed and on the other hand, use a cutter or x-acto knife to trim a bit of the spool-holder part so I will fit snug over the frame.

Kit printed parts quality was quite good but I have got one crack on one of the Y-axis corners when pressing the smooth rod the first time. Other than that nothing broke and nothing was missing, but one picture showed the nut of the PINDA probe while that nut was missing. However, the text warned that if present it was to be removed. I had to use a couple of extra M3x30 screws for joining the PSU to the Y-axis frame (a change of size was mentioned in the manual).

I just can't wait for an MK3 kit that is coming my way in a few days. I hope it will work better than the sample printer delivered to Thomas Sanladerer


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