Prusa i3 MK3S – setup and calibration

Probably one of the most frustrating things about getting a precision machine is having to ensure that it is actually, well, precise. A 3D printer is a CNC (Computer Numerical Control) and it is only capable of doing what you tell it to do based on assumptions that its parts are where it expects them to be. For a 3D printer, ensuring that the X-Y-Z axes are all perpendicular and getting the correct nozzle height to extrude just the right amount of molten plastic are essential to happy printing. While the Prusa MK3S is touted as a fairly plug-and-play type printer (and a big factor in my purchasing it), even it requires some time to get fully calibrated. After all, this is a printer that costs less than $1000 in an industry where 3D printers often go for many thousands more.

I won’t lie and say that setup and calibration were quick and easy. In fact, it took many hours of testing and tuning before I was satisfied. My axes were perpendicular but getting the nozzle height tuned in was a challenge. For someone who had never seen 3D printing in person before, it was difficult to know what a good extrusion looked like (even with the aid of pictures in the manual). It took many cycles of printing, observing, and tuning to get the printer calibrated to a level that I could live with. I wasn’t expecting perfection, but I wanted it to be as close to perfect as possible.

For the most part, I followed the manual and performed the first layer calibration. This was only somewhat helpful but it was a necessary step to get you quickly through 80% of the journey. Unfortunately, the remaining 20% would take a lot of patience and time.

bed level correction Prusa style

After setting my first layer calibration through the menu option, I moved onto more advanced calibration. For me, this included bed level correction and extrusion multiplier calibration. Although the printer already performs mesh bed leveling prior to every print job, the bed level correction would further adjust the nozzle height in four directions to account for imperfections in the build plate/head bed. As a 3D printing beginner, I had assumed the mesh bed leveling would be enough to account for these imperfections because that is what it’s for (or so I thought). The printer probes the print surface using the P.I.N.D.A. probe (pictured above) to determine differences in height of the heat bed, allowing the printer to dynamically adjust the nozzle height as appropriate. Unfortunately, it seems automated mesh bed leveling is fairly limited to large distortions and a manual correction is necessary to fine tune what the probe could not.

I started using the bed level correction STL provided by Prusa and was quickly able to tune the printer to give me satisfactory for that specific STL. However, when I printed something that wasn’t the calibration STL, I was given a first layer that was not what I was given with the calibration print. I didn’t understand what was going on. Was it my extruder tension? Was I missing something?

bed level correction my style

I decided to create my own calibration model, which was essentially a large rectangle that covered almost the entire build area and was one layer thick. My thinking was that it would allow me to tune the bed level correction numbers to ensure that all areas of the bed would have satisfactory first layers. Although this print would take nearly 2 hours to complete, I thought it was worth it to ensure my first layer would be consistently good and I could trust sending jobs to the printer without having to babysit it every time.

My first print revealed that much of my bed was too close to the nozzle. Something that was impossible to gauge using the first layer calibration and even the bed level correction STL provided by Prusa. After making some adjustments, I was able to fine tune the correction values to a smooth, even first layer on 95% of the calibration print. There was a small portion on the right side my build plate that would consistently under extrude. Calibrating the numbers to correct this resulted in the majority of the build area being over extruded. As a result, I decided to focus on the majority and just accept that I would likely not be able to print anything that required that area of the build plate.

I flipped the steel sheet over to determine if whether the other side had less imperfections, but it seems it had its own set of imperfections that would need a whole new process of bed level correction, which I just wasn’t prepared to do. I just wanted to get to printing actual things, not calibration things. So, I flipped it back to the side I had been using and ran one more calibration print just to make sure I was getting consistent results with the same bed level correction numbers. Thankfully, I did.

extrusion multiplier calibration

After all that bed level correction madness, I was happy to find that extrusion multiplier calibration was fairly simple. All it took was one print, some measuring with my digital calipers, and finding out that I didn’t really need to adjust the value set in the slicer.

at last, happy printing

It’s amusing that the Prusa setup wizard displays “Happy Printing!” after completing the first layer calibration when in reality, there is still so much more calibration to do for high quality prints. While I knew it wouldn’t be completely plug-and-play, this much calibration was definitely more than I was expecting. If this is what I needed to do to dial in the highly touted Prusa i3 MK3S, what would I need to do if I had purchased the much cheaper Creality Ender 5? Honestly, I may eventually get a Creality machine for the larger build area, but not until I’ve become much more experienced in 3D printing.

I actually still want to do the extruder linearity correction calibration, but right now, I just want to start printing. If I notice the signs that require this calibration, I’ll do it at that time. I look forward to sharing my 3D printing projects. Check out my TO DO post for a list of projects I currently have in mind. As always, questions and comments are welcome!

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