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Building the Original Prusa i3 MK3: Review the Facts Here!

Picture of Bulent Yusuf
by Bulent Yusuf
Jan 12, 2018

We've put together an Original Prusa i3 MK3 DIY 3D printer kit, and we want to tell you all about the assembly process. Review the facts on the latest and greatest desktop 3D printer from Prusa Research.

It’s smiles all round here at ALL3DP, where we’ve had the pleasure to unbox and assemble a brand-spanking new Original Prusa i3 MK3.

Join us on a journey of self-discovery; assembling the new Original Prusa i3 MK3 DIY 3D printer kit.

We’d like to clarify that this isn’t a full review of the MK3. A detailed appraisal of the machine’s performance comes later, when we’ve had a chance to properly put it through its paces.

In the here and now, we want to share with you our experience of assembling it. And also, as we go along, to point out the key differences from the MK2S that we found. It’s been a wild ride.

We’ve taken pictures for each stage of the build. Please forgive us for the crappy lighting and out of focus shots. The immediacy of the build took priority over professional studio conditions.

Don’t Miss: All3DP Visits Josef Prusa at the New Prusa Research Facility


Original Prusa i3 MK3 Review Introduction

Image of Original Prusa i3 MK3 Review: Introduction

So what’s the big deal about the Original Prusa i3 MK3? It’s pitched as a refinement of everything Prusa Research have achieved to date; more than a reliability upgrade, but a new and improved desktop 3D printer with some awesome new features.

Where the previous model offered astonishing print quality for the money, the Original Prusa i3 MK3 seeks to make the discipline of fused deposition modeling (FDM) more intuitive and easier than ever before, with a plethora of sensors to alert users to potential problems and prevent failed prints.

There’s a lot to cover, but to summarize those new features:

  • Filament sensor
  • Power Panic
  • RPM sensing fans and Noctua
  • Ambient thermistor and P.I.N.D.A 2 with thermistor
  • EINSY RAMBo motherboard
  • Trinamic2130 drivers with layer shift detection, faster and silent printing
  • New Y axis
  • Bondtech extruder
  • Magnetic MK52 Heatbed
  • Powder coated PEI spring steel print sheet
  • Ready for OctoPrint

The Filament Sensor uses an optical filament encoder to detect the presence and movement of a filament. This provides early warning for when the filament is about to run out, and the machine can pause the print and prompt the user to insert a new spool. It can also detect stuck filament and recommend a “cold pull” to clean the nozzle and continue the print.

Other upgrades are Power Panic, where the MK3 can recover and resume a print-job after a power loss, and a new EINSY RAMBo motherboard which is pitched as the most advanced 3D printer board currently available. How advanced is it? It can monitor power, for one, which allows for the detection of blown fuses. For another, it features Trinamic drivers which are super fast, quiet, and can detect (and correct) layer shift while printing.

Elsewhere, the Original Prusa i3 MK3 has a reworked Y axis for improved frame rigidity and an extra 10mm build volume on the Z-height. And there’s an upgraded Bondtech drive gear extruder, which grips filament from both sides to increase the push force of the filament and making it more reliable (especially for flexible filaments).

But perhaps the biggest highlight of the MK3 is the new MK52 Magnetic HeatBed, which holds detachable alloy spring steel sheets powder coated with PEI. As the sheet cools down, parts can be popped off by simply flexing the sheet.

So! Without further ado, let’s move onto the unboxing and build, shall we?


Original Prusa i3 MK3 Review Unboxing

Image of Original Prusa i3 MK3 Review: Unboxing

Excuse the messy desk. All the necessary components for the Original Prusa i3 MK3 kit are clearly labeled, securely packaged, and stamped with the Prusa Research logo.

Cracking open the boxes, you’ll find the components for each specific stage of assembly even further itemized. Some of them also carry QR codes, serial numbers, or ID stamps for the individual doing the picking and packing.

This kit is clearly the product of a thorough and complex operation at Prusa Research, and it’s hard not to feel daunted. Where to begin, exactly? What goes where? Can we start absent-mindedly start popping the bubble wrap yet?

Fortunately, there are two important items you’ll immediately find at the top of the box. The first is a packet of Haribo candy. The second is a note offering you congratulations on your purchase, plus information on where to find your instruction manual.

Also included are a set of essential tools for the task; a pair or needle-nose pliers, a set of hex keys, plus two screwdrivers and a large packet of plastic zip-ties (you’re going to be using a lot of them).

These instructions and these tools are everything you need. However, in building the Original Prusa i3 MK3 we would also suggest you source a pair of tweezers for handling the smaller components, and — don’t laugh — a dry towel for wiping sweaty fingers.


Original Prusa i3 MK3 Review Y-axis Assembly

Image of Original Prusa i3 MK3 Review: Y-axis Assembly

The first stage is to assemble the Y-axis frame, and this is where you notice one of the most obvious improvements over the MK2. The base is no longer constructed from threaded rods but from aluminum rails and aluminum front and back plates.

This is a major step forward in frame stability, and provides an extra 10mm of Z-height when printing.

This design change also means a new set of printed parts for the linear rails and the belt pulley, though the system of u-bolts to keep the linear ball bearings in place remains the same.

Most intriguingly, the end-stop switches are entirely absent from this build. They’re no longer required for X/Y axis homing, thanks to the Trinamic2130 drivers on the new EINSY RAMBo motherboard. This is very welcome, not least because it simplifies the build process considerably.

One thing we noticed at the end of this stage was a handful of leftover nuts. According to comments on the instruction manual, other users have experienced the same. This isn’t a showstopper, however; the nuts are simply surplus to requirements.


Original Prusa i3 MK3 Review X-axis Assembly

Image of Original Prusa i3 MK3 Review: X-axis Assembly

This second stage of assembling the Original Prusa i3 MK3 is perhaps the easiest, but some delicacy is required.

Putting together the X-axis involves a pair of linear rods, seven linear bearings, an X-axis motor. What holds it all together are the 3D printed components, nuts and bolts, and judicious application of zip-ties.

Where you have to be absolutely careful is the rods and bearings themselves. They’re precision items, and any bending or careless handling will impact on the performance of the printer later on.

Comparing this stage of the build to the MK2S, meanwhile, we couldn’t see any huge differences in design or assembly. The only key change is the X-carriage itself, which has been redesigned to accommodate the new bells and whistles (not literally) of the MK3.

At this point, we should mention quality control about the 3D printed components. While the surface of the new parts have a nice texture where they were printed face down on (we presume) the new magnetic beds, we noticed some niggling flaws here and there.

The redesigned X-carriage has a channel on the back to tuck away cables from the filament sensor, and here there are discernible fissures at the bottom of the channel. Since we’re talking about fused deposition modelling (FDM) here, our diagnosis is that it’s not a problem with layer adhesion but with bridging.

It’s not so bad as to give us concerns about impact on performance, but it’s something to keep an eye on.


Original Prusa i3 MK3 Review Z-axis Assembly

Image of Original Prusa i3 MK3 Review: Z-axis Assembly

This is the juncture where we commence the Z-axis assembly, and this is the point where our labors start to resemble a desktop 3D printer.

What you have to do here is mount the X-axis from the previous stage to the Z-axis. That requires first mounting the X-axis motors on either side of the frame, and then the threaded rods and bearings, and then slapping the X-axis rails on top.

Well, not slapping exactly. The threads on the metal frame are very stiff, and require a firm hand to screw the bolts in without breaking the 3D printed components.

That, plus ensuring the X-axis rails are perfectly level. Threading it too far in one direction would be catastrophic for the 3D printed components, causing them to crack.

Let’s replace the word “slap” with “gingerly mounting” shall we?


Original Prusa i3 MK3 Review E-axis Assembly

Image of Original Prusa i3 MK3 Review: E-axis Assembly

This fourth stage is the most labor-intensive and the most delicate, with the manual specifying 48 steps.

One immediate gripe we had is that a lot of time was spent on the idler assembly stages. The tolerances for several components were extremely tight.

And wowee, if you have a fetish for proper cable management, then from here on out you’re going to be giddier than a swine in fertilizer. The guidance is extremely thorough.

All that said, the E-axis assembly is also our absolute most favorite part of building the Original Prusa i3 MK3. This is the point where you can really marvel at the design genius of Jo Prusa and his team, where so many disparate elements come together in harmony.

Just comparing the MK3 version with the MK2S version, you can discern how much more elegant and yet more complicated it is, accommodating proven components like a Bondtech extruder, the E3D V6 hotend and the PINDA probe together with the filament sensor and the quieter fans.

As stated already, this is not an Original Prusa i3 MK3 review. So we can’t tell yet precisely how well things like the new filament sensor or the new fans are going to work. But the engineering is truly extraordinary.


Original Prusa i3 MK3 Review LCD Assembly

Image of Original Prusa i3 MK3 Review: LCD Assembly

After the epic bout with the E-axis assembly, we move on to something considerably more relaxing.

The LCD control panel is virtually identical to the version supplied with the MK2S. It’s a simple matter of inserting a combined circuit board and LCD screen into a plastic case, adding a button, and then mounting it to the front.

But for the second time during this build, we felt that the quality of the printed parts was lacking somewhat.

It’s the same problem as before; the control panel has been 3D printed face down, with a nice texture on the surface. But where the “Original Prusa” engraving is located, the bridging on the embossed characters is ugly. Holding this part up to a light source, you can clearly see through it.

We would guess that the remedy would be to print it again, but thicker. Or slower. Or we might just swap out the case from the MK2S instead. This should be a very easy thing to fix.


Original Prusa i3 MK3 Review Heatbed and PSU Assembly

Image of Original Prusa i3 MK3 Review: Heatbed and PSU Assembly

The most important thing about tackling a DIY 3D printer kit by yourself is to maintain a good sense of humor. And it certainly helps when the kit itself provides some entertainment of its own.

Tucked away on the underside of the heated bed of the Original Prusa i3 MK3 are lots and lots of magnets. Super-strong magnets, to hold the removable metallic printbed in place, which is another new feature of the MK3.

At this juncture, we were delighted to find a nice little Easter Egg.


Not quite sure what a neurostimulator is; but you don’t want to handling this item whilst wearing a mechanical wristwatch.

The rest of this stage is nice and easy; affix the heated bed and power supply unit to the frame. Some basic cable management comes into play. No problems to report.

In terms of design changes, the big difference here is that the MK3 now has 9 screw points to hold the bed flat, compared to 6 screw points on the MK2S.


Original Prusa i3 MK3 Review Electronics Assembly

Image of Original Prusa i3 MK3 Review: Electronics Assembly

Phew, this stage is the second most complicated after the E-axis assembly. Taken together, the cable management and wiring the electronics board is very much akin to performing open heart surgery (we would imagine).

For the first part, liberal applications of zip ties are needed for wrestling the cables into submission, but there’s a logical (and lengthy) process outlined in the instruction manual.

For the second, you need to plug the ends of those cables into the board, and do so without pinching the cables or plugging it into the wrong sockets. Of particular importance are the cables from the power supply unit and the heated bed.

A steady hand is required, as is a rigorous observation of the guidelines, so dial back on the caffeine a notch.

Key differences from the MK2S are that the RAMBo cover has been subtly redesigned with more cooling vents.

And of course, the RAMBo board itself, which is completely brand new. There are actually two versions of this board in the wild; our version of the motherboard has a daughterboard attached, to accommodate new connectors from the LCD control panel.

Once we were done, it took some effort to close the lid on the whole tangle of wires. Considering that you’re supposed to be able to add a Raspberry Pi Zero W at a later stage for OctoPrint and wireless connectivity… Well, we’re not sure how we could get one to fit in there, regardless of how tiny it is.

And with that, the build of the Original Prusa i3 MK3 is now complete. But there’s still calibration and test prints to come.


Original Prusa i3 MK3 Review Calibration

Image of Original Prusa i3 MK3 Review: Calibration

It’s squeaky bum time. Because while building a 3D printer is definitely an achievement in itself, the calibration and self-test is where you learn that everything has been assembled correctly. And if you find that it isn’t, then that’s the cue for a bit of head-scratching where you try and troubleshoot.

First are the preflight checks; before you plug in and power-up the Original Prusa i3 MK3, you have to adjust the PINDA probe to the correct height in relation to the hotend.

This bit is delicate, because it requires you manually lower and move the hotend on the Z and X axes, and you have to be careful not to score a deep groove into the heated bed with the hotend.

Next, you power up the machine and check that you have the latest firmware. If you don’t, then you must source the latest drivers and firmware from Prusa Research and follow the instructions for the update process.

A curious wrinkle here is that Windows and MacOS users are well catered for, but Linux users have to jump through a few more hoops. Since this is open source hardware, we expected the open source software support to be more sophisticated.

Finally, you can initiate the setup wizard from the LCD control panel. This is where the MK3 runs a series of self-tests and calibrates itself on the XYZ axes. Once those are passed, you’re prompted to load up the supplied filament and run some real-time adjustments.

All in all, the process is rather painless. If you’ve followed the build guide properly AND if there isn’t a catastrophic failure with the electrical components — and there won’t be, since every kit is issued with a testing protocol — then you’re going to be okay.


Original Prusa i3 MK3 Review Simple Test Prints

Image of Original Prusa i3 MK3 Review: Simple Test Prints

So now you’re ready to print. The SD card comes preloaded with lots and lots of models that have been pre-sliced by the team at Prusa Research, so it’s a case of taking your pick from what’s available.

We opted for three small but simple models for the first stage of test printing. We just need to ensure that the 3D printer is operating in principle. So all that’s required is printing something fast and easy.

So what have we made? First is a simple Prusa badge. Second is a 3DBenchy, pictured above. Third is a small but cute model of Buddy, Josef Prusa’s pet dog.

Seeing the printer in action is a real delight, and some primary observations are as follows; firstly, the MK3 is very very fast; secondly it’s very very quiet; thirdly, the removable bed makes popping off the prints an absolute breeze.

The 3DBenchy wasn’t totally perfect; there was some warping on the prow. And little Buddy is suffering from layer shifting. We suspect the latter happened because we activated “stealth” mode in the settings; this provides the benefit of silent operation but also deactivates the shifted layer detection in the Trinamic drivers.

Not perfect, but the important thing right now is that it works. High fives all round.


Original Prusa i3 MK3 Review Advanced Test Prints

Image of Original Prusa i3 MK3 Review: Advanced Test Prints

A-ha! Bet you though were done with test printing, eh? So were we, truth be told. But a string of firmware and driver updates came down the pipe from Prusa Research, so we felt obliged to run a few more.

We decided to be a bit more ambitious this time out, and opted to print some bigger, more detailed models that took longer to make.

Preloaded on the SD card were the bust of Nefertiti (a 3D scan of the real thing obtained by dubious means), a beautiful singing dragon named Adalina, and a fairy-tale castle straight outta Disneyland. All of them were excellent.

Interesting to note is that, since the firmware update, despite these prints being much more demanding the quality of the results were outstanding. Prints were fast, clean and quiet.

Also worth mentioning is the infill being employed; it’s a three-dimensional triangle pattern we haven’t seen before, which is engineered to be strong and durable. Watching it being formed layer-by-layer is hypnotic.

Fine-tuning and slicing our own models using the PrusaControl software comes later in the full Original Prusa i3 MK3 review.

original prusa i3 mk3 review

Original Prusa i3 MK3 Review Pricing and Upgrades

Image of Original Prusa i3 MK3 Review: Pricing and Upgrades

In terms of pricing, the Original Prusa i3 MK3 retails in kit form for around $900. Its predecessor the MK2 is also available in kit form for around $725.

Prusa Research is also offering a series of upgrade kits for owners of the MK2 and MK2S models, and will release an upgrade kit for multi-material printing, including filament sensors for all 4 extruders. You can review the full set of options here.

Last but not least, the new EINSY RAMBo board has a special accessory header for connecting a Raspberry Pi Zero W. This is perfect for adding OctoPrint functionality to your 3D printer; Prusa Research plans to provide a special firmware distribution for wifi connectivity from the printer LCD interface.

Referring to our specific experience, potential upgrades that we’d suggest would concern the 3D printed parts themselves. We’re not suggesting that the parts that come with the kit are faulty, but there were some minor quibbles over quality control. And there’s always a chance of breaking a piece during the assembly process if you apply too much force.

Fortunately, if you already have access to a 3D printer you can easily print off a spare set. And with the new version control system implemented with this generation, you’re always going to know whether you have the most current set of parts for the Original Prusa i3 MK3.

We’ve been given to understand that the factory parts are printed in PET-G material, so you probably want to stick with that. Though ABS is also a viable material, since that was used in previous models. And if you have money to burn, you could even get them made with laser-sintered nylon. That would be awesome.

Another suggestion would be to swap the linear ball bearings for polymer ones. Doing so will dramatically cut down on the amount of noise generated by your 3D printer. They can also be used dry without the need for lubrication. It’s a very simple but effective upgrade.

Finally, a small upgrade to the E3D V6 hotend would be to procure one of those blue silicon socks. It’s really good for keeping the hotend clean, and prevents grimy bits of charcoal from futzing up your prints.


Original Prusa i3 MK3 Review Wrapping Up

Image of Original Prusa i3 MK3 Review: Wrapping Up

First and foremost, we’d like to raise a glass to Jakub Dolezal for his fantastic work as a technical author. He’s produced a set of instructions to assembling the Original Prusa i3 MK3 that are legible, clear and free from error. Thank you, Jakub!

At no point were we left scratching our heads or wondering what to do next. Moreover, the structure of the guide is such that other users can contribute comments or feedback; more often than not, this feedback goes upstream into either improving the guide or improving the design of the printer.

Which brings us to another important point about building the Original Prusa i3 MK3; witnessing iteration in action. In studying the construction of both the MK2S and the MK3, it’s clear that there is some serious design evolution at work.

Josef Prusa and his talented team are not content to rest on their laurels, they’re constantly striving to deliver the best 3D printer they possibly can. Here at ALL3DP, we’re cautiously optimistic that the Original Prusa i3 MK3 may well turn out to be that printer. Detailed review to follow very soon.

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