Prusa i3 MK3 Review

Prusa started the i3 style printers but the printing industry has expanded well beyond the original Prusa i3 to include many i3 clones. These clones are often cheaper and many print quite good. With these readily available clones, should you still be buying Prusa brand printers?

Image of prusa i3 mk3
Image Credit: Prusa3D

I bought the kit version of the Prusa i3 MK3 printer in early March and received it early May (note: mine came with B2 parts). My MK3 was not a review unit so I did not get the fancy powder coated PEI spring steel sheet that showed up with reviewer models. I still don’t think they are shipping the powder coated PEI sheets in any kind of volume so my recommendation is base your purchase on the performance of the double sided PEI sheet instead (spoilers: it works fine).

So what does the Prusa i3 MK3 have that the Prusa i3 MK2S (and older) doesn’t have?

MK3 new features

Removable build platform

The Prusa i3 MK3 has a magnetic bed that a spring steel sheet connects to magnetically. The spring steel comes with a PEI sticker on both sides allowing you to flip it if one side gets damaged. Damage, however, should not be an issue like it was with the MK2S and earlier because the spring steel flexes. This usually allows parts to pop off the build plate with ease saving you from scraping and, ultimately, damaging your build plate.

Filament runout detector

If the Prusa i3 MK3 senses your filament has run out, it will pause the print and wait for filament to be reloaded. While I have not tested it, the printer should also be able to sense if filament is not moving through the extruder. This feature comes turned off because there are filaments it does a poor job of detecting like clear or white colors. I think the idea was great, but ultimately over engineered resulting in a feature most people will likely leave off. That said, when I’ve tried it, the sensor worked perfectly for opaque and non-white filaments. What would be better, of course, is a detector that works with any filament.

Crash detection

I tested this involuntarily. I left a print going and a blob of hardened PETG snagged the nozzle and resulted in crash detection. The MK3 stopped, raised the extruder and moved to the side. The only odd part is it tried to resume with no user interaction. This caused a second crash because the now mangled part was still partially stuck to the bed. If you can tell it to pause and wait for user intervention this would be a fantastic feature.

Bondtech gears

Bondtech figured out that gripping filament from both sides was better than just one. The MK3 incorporates the Bondtech gears in their custom extruder and results in vastly reduced filament slipping, especially with flexible filaments. This also helps filament feeding resulting in filament never missing the hotend entry hole. This alone is worth the Bondtech upgrade on any direct-drive printer for people looking to print with flexible filaments.

Power resume

If you lose power in the middle of a print usually that means the end of the print. In this case it means, if everything works as it should, the printer will use it’s last bit of power to raise the head and resume when the power is restored. The one time that this happened it worked as described, although don’t expect that next layer to be perfect.

Noise reduction

Do you live in an apartment or don’t have a basement or garage to do your 3D printing in? If so this is a Godsend. It is truly the quietest printer I own. It is so quiet there are times you forget it is running. This is due to improved stepper drivers and using a Noctua fan for the hotend cooling. If you are into building custom PCs then you should know the Noctua brand. They have a reputation for making suspiciously quiet fans that still perform well. How? Unicorn dust probably.

I am more likely to pick the MK3 for printing because I know it will be quiet and that says a lot about how great a feature this is for people who live in smaller living spaces.

Hardware

My Prusa i3 MK3 has been rock solid over 230 hours of printing. No nozzle jams across a variety of filaments including PLA, PETG, and wood fill. The leveling sensor and steel spring sheet perform perfectly and I have not once had a failure while loading filament.

I have printed probably 50% PETG and 49% PLA and 1% other filaments so the printer has seen a range of temperatures during printing from as low as 185c to 250c at the highest. Throughout printing temperatures have remained stable and the printer reliably heated the hotend and bed.

The Prusa i3 MK3 is packed with features that make printing less frustrating. The removable spring steel sheet is fantastically implemented. Popping a print off without a paint scraper is such a satisfying feeling. With PETG filaments they would stick almost too well to the PEI sheet and popping them off would result in micro-bubbles under the surface. These bubbles do not show up in print surfaces and do not otherwise appear to cause an issue with prints. To avoid this you could use something like glue stick in between the PETG and PEI.

The filament detection is a little disappointing. I know Prusa is somewhat adverse to mechanical detection (especially roller switches), but I would rather have something that might wear out and need to be replaced but works with every filament than the current solution which only works with certain filaments. When it does work, with the correct filament colors, it works flawlessly in my experience.

Software and Firmware

Prusa provides the complete package of hardware, custom firmware, and slicing software. This allows them to tweak each important element that significantly impacts the printer. I criticized MatterHackers Pulse for basically doing the same thing except, in the case of Prusa, they are providing not only complete Marlin Firmware feature set (software the runs your printer) but they’ve added their own improvements and features.

Prusa’s Slic3r slicing software is feature rich, modern, and tweaked to work with the Prusa printers. You do not see this level of quality integration except from more expensive printers like the Ultimaker line up.

Printing

There is a vocal portion of the Prusa community that insist the MK3 prints worse than the MK2 or MK2S. The main complaints focus on inconsistent layers. To be incredibly confusing I am going to say yes I see it and no I don’t.

Inconsistent layers are a hard thing to qualify. Many things can cause issues including inconsistent filament width, model design, poorly tuned extruder, poor temperature stability, a Z frame issue, extruder gear issues, and loose belts. All of those things can make it difficult to figure out the cause of this issue.

To give you an idea of the range of quality you can expect look at the prints below:

This Dragon print came out great:

Dragon print with minimal layer shifting

The Triceratops does not look nearly as good in some places:

Triceratops with visible inconsistent layers

The Unicorn, however, looks pretty smooth:

Smooth Unicorn print

And finally my print of a Gargoyle that has some inconsistent layers:

Statue with somewhat inconsistent layers

These all printed on the Prusa i3 MK3 with similar settings. The major differences? The model and the filament.

So what’s my point? Some filament and/or models show layer inconsistencies better than others. Prusa happens to ship a filament, Prusa Silver, that shows layer lines better than other colors. For new owners, the first prints they make will be with this Silver filament which may draw their attention to the issue more so than other new printer buyers with different filaments.

A lot of printers, especially bed slingers like the Prusa i3 MK3, will have layer inconsistencies. The forces moving the various axises are not perfectly compensated. FDM printers, especially ones in this price range, are not going to be precision machines. This means most FDM printers will show at least some inconsistencies in prints.

The real question should be: Does the Prusa i3 MK3 produce prints that show more layer inconsistencies than similar printers?

Maybe.

Thomas Sanladerer recently interviewed Josef Prusa and asked specifically about the inconsistent layers and he brings up some of the things I’ve talked about here, but added that there might be slightly worse performance over previous Prusa printers due to the Bondtech gearing. I think Josef was reluctant to mention it because they are still researching the potential issue so I would not jump to the conclusion that Bondtech gearing is always a problem.

My advice for people interested in the MK3 is look at the thousands of prints out there from Prusa i3 MK3 owners, both good and bad, and decide if you are willing to accept similar quality prints. If you watched the video above or read Prusa community comments and think the gears might be contributing, wait to buy the MK3 and see if they find more evidence of it being an issue or buy the MK2S (or another brand printer) which does not have Bondtech gears.

Support

Prusa is growing fast and you can see it affecting their support’s quality of response and speed of response. I think they are going through some growing pains as a company, but I expect their support to improve.

In my experience sales support have a decent turnaround and usually informed responses. For hardware issues it really depends on who you get in contact with. A vast majority of common build issues are answered in the forums by other users and because the community is so large. There is a good chance someone will have experienced whatever issue you’ve run into already.

Communities are great, but are no substitute for well trained company support who know the products inside and out and, from what I’ve read, they’ve got a bit of a mixed track record with support responses. I think Prusa knows this and are working to improve their entire operation so I hope they can get back to being a company that provides great support in an industry where other manufacturers offer little to zero support.

Conclusion

I personally like the Prusa i3 MK3. It may not offer anything over the MK2S in terms of print quality, but the connivence features are a big deal. Reduced noise, easy print removal, collision detection, power out resume, and, when it works, filament runout detection have me coming to the MK3 first before my other printers.

When it comes to clone i3 printers you see a mix of the features Prusa’s MK3 has but usually never the complete package. Also take into consideration most clones won’t have well developed firmware and custom slicer software like original Prusa products. With these features you can see why Prusa keeps growing as a company.

Positives

  • Removable bed system that works every time
  • Very quiet
  • Solid design that improves on the already good MK2
  • Printing is consistent
  • Huge community of owners
  • Comes with genuine E3D and Bondtech parts
  • Direct drive
  • Firmware, Software, and Hardware integration

Negatives

  • Company growing pains with support
  • Filament runout detector only works with certain colors
  • Print quality may be slightly worse than MK2 models
  • Kit is more complicated to build than other newer kit 3D printers
  • Promised powder coated PEI sheets are in very limited supply

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