The Original Prusa Mini ($349) has a modest price tag but is big on both performance and reliability. This open-frame 3D printer, which is sold as a kit, is fairly easy to assemble but required some tweaking to get up and running properly in our tests. Once it was correctly set, however, it performed like a boss, printing out a variety of objects with no misprints and good handling of detail. It’s an easy pick as our newest PCMag Editors’ Choice winner for low-cost 3D printers.
The Man, the Company, the Legend
Prague-based Prusa Research is legendary both for its phenomenal growth as a business and for the role of its founder in the development of filament-based 3D printers. Prusa 3D printers are the brainchild of Josef Prusa, a Czech maker who first got interested in 3D printers as a way to produce knobs for the audio equipment he loved. He became a convert to the open-source RepRap movement for self-replicating desktop 3D printers—”self-replicating” in the sense that a RepRap 3D printer can print plastic parts for use in building additional RepRap printers.
Out of RepRap came the basic designs used in most of the fused filament fabrication (FFF) 3D printers marketed to hobbyists, makers, and consumers. Today, in the company’s Prague headquarters is a large hall called The Farm in which more than 500 3D printers churn out parts for other printers.
In 2010, Josef Prusa created the Prusa Simplified Mendel, a redesign of the original RepRap Mendel printer, and uploaded the design for other makers to build. He started manufacturing 3D printers, and in 2011 came out with the second iteration of the Prusa Mendel, the i2. (The Original Prusa i3 MK3S, Prusa Research’s current flagship 3D printer—which PCMag will soon be reviewing—is the most recent model in that lineage.) In 2012, Josef and his brother Michal Prusa founded Prusa Research, which to date has sold more than 200,000 3D printers worldwide.
Assembling the Original Prusa Mini
Unlike the Original Prusa i3 MK3S—which is available either preassembled ($999) or in kit form ($799)—the Prusa Mini is sold only as a kit. The base model costs $349. Our test unit also included a filament sensor ($20) and a second, textured build plate ($30), as well as a spool of PLA filament ($24.99). Note that the kit comes with just two small starter packets of filament.
Shipping to the U.S. via FedEx or DHL costs an approximate additional $50. On purchases of more than $800, American customers may have to pay an import duty on receipt, but that won’t be an issue with this puppy.
In light of the Original Prusa Mini’s RepRap origins, it feels absolutely fitting that it comes as a kit, although much of it is admittedly preassembled. As far as kits go, the Prusa Mini is fairly straightforward to put together. Assembly does not require any tools beyond the included Allen wrench.
The small inventory of parts includes the two main parts described below, as well as an LCD and its cable, the build plate, the spool holder, the power supply, some foam pads, and a small number of screws. Plus, you get one unusual addition: a small package of Haribo Goldbären—better known in the U.S. as Gummi Bears—to be doled out as rewards for completing certain steps, as specified in the Assembly Manual.
The combined Assembly Manual/3D Printing Handbook, which is a beautiful, professionally printed guide, is one of two assembly aids. The other is a YouTube video, The Original Prusa Mini: Unboxing & Assembly, narrated by Josef Prusa…
It’s a good idea to read and watch these instructions before starting. The estimated build time, according to Prusa, is 50 minutes, though it took me a bit over two hours to complete.
To assemble the Prusa Mini, you first peel the backings off of five foam pads and affix them to the bottom of the printer’s main components. You then open the electronics box and snake one end of the LCD cable into it, snapping it into its socket. Then you’re ready for the trickiest part of assembling the Prusa Mini: fastening the two main components together.
The first is the Y-axis assembly, which includes the print bed, its motor, and a carriage along which, during printing, the bed moves in and out (along the so-called Y-axis when pictured in three dimensions). The second is the XZ-axis assembly, a tower holding the extruder assembly, which can be raised or lowered (along the Z-axis), or moved side to side (X-axis), plus related motors and fans, and the electronics box.
Uniting these two parts involves aligning the somewhat heavy and awkwardly shaped parts, then positioning several bolts to line up with holes so they can be screwed into place using the included Allen wrench. Even seeing the bolts was at times difficult, and it took me a while to complete this step.
After you have connected these parts, you bolt the LCD to the front of the Y-axis assembly, attach all the cables to their proper sockets in the electronics box, assemble the spool holder (a cradle on which the filament spool sits), and attach the build plate. (It adheres magnetically to the print bed.) Connect the power supply to the printer and an outlet, and you’re done.
What you end up with is an open-frame, orange-and-black printer, measuring 14.6 by 13 by 15 inches (HWD). The build area is 7 by 7 by 7 inches, fairly large for its price. That said, both the XYZprinting da Vinci Jr. 1.0 A Pro and the Monoprice Voxel 3D Printer have nearly identical build areas of 6.9 by 6.9 by 6.9 inches.
Calibration Highs and Lows
When you first turn it on, the Original Prusa Mini’s LCD panel lights up, and the printer runs through a self-test routine. This ensures that the extruder and the build plate heat properly, that the cooling fans operate, and that motion along the X, Y, and Z axes is unimpeded. It was a thrill to see the machine run through that routine for the first time and have everything come up green.
Once the automated tests are done, you are invited to perform a first-layer calibration to set the so-called Z-axis offset. In layman’s terms, you are setting the distance between the extruder nozzle and the build plate when printing the first (bottom) layer. The idea here is to lower the extruder close enough to the build plate so that in printing the first layer, the molten filament squishes against the print bed, letting it adhere to the build plate. You don’t want to bring it so low, though, that the nozzle could make contact with and scratch the plate.
The procedures for this first-layer calibration are laid out in the handbook, and also described by Josef Prusa in a video called Original Prusa Mini: Calibration and First Print…
When you launch the first-layer calibration routine from the printer’s LCD, the extruder heats up, touches 16 points in a square grid on the print bed to ensure that the bed is level, and then prints out a test pattern. This pattern is a series of horizontal lines connected by short vertical lines, culminating with a small rectangular box filled with closely spaced parallel lines. You then compare it with diagrams in the manual to see if the nozzle height was correct.
If the filament is ropy and the lines poorly formed, the nozzle was too high, and if the lines are thin with only a small amount of filament extruded, the nozzle was too low. You can adjust the nozzle height while the test pattern is being printed by rotating a knob at the bottom of the LCD.
With most 3D printers that offer first-layer calibration, you set the Z-axis offset when the extruder is stationary, by placing an index card or a business card between the build plate and extruder, then lowering the extruder in increments until you feel some resistance when pulling the card out. This kind of straightforward routine can be done in a minute or less. Calibrating the Original Prusa Mini can be much trickier, though.
After lowering the extruder a bit, I tried printing a test object, a plaque with the word “PRUSA” on it, but it quickly pulled off the build plate. I ran the first-layer calibration again and again, each time lowering the nozzle a little bit more, but the objects continued to pull off the plate during printing.
It was hard to tell how far the extruder was above the build plate while the nozzle was extruding filament, and even hard to compare the printed filament’s thickness with its appearance in the diagram. Finally, I got the Prusa Mini to print several objects successfully, but when I tried our standard tall geometric test object, it pulled off the build plate a bit before it reached the top.
I lowered the nozzle again and switched from the smooth build plate to the textured one, hoping objects would adhere to it better during printing. I had no further problem with objects pulling off, and I was able to successfully print the geometric test object this time. Eventually, I switched back to the smooth build plate and had success with it. The filament was more squashed than the image in the printing handbook suggested it should be for proper printing, but it worked.
Filament, Connectivity, and Software
The Original Prusa Mini includes two small starter packets of filament and comes with an easy-to-assemble spool holder. You will want to purchase additional filament at the get-go.
This model supports a fair variety of filament types, including PLA, PETG, ABS, ASA (acrylonitrile-styrene-acrylate, an alternative to ABS), and Flex. Prusa sells its filament (dubbed “Prusament”) for $24.99 per 1-kilogram PLA spool and $29.99 per PETG or ASA spool. You can also use third-party filament, which should be more cost-effective than having Prusament shipped from the Czech Republic.
Connectivity is via Ethernet (connecting the printer to the same network as the computer you are printing from), or a USB thumb drive. In my testing, I saved files to print out to the USB key that came with the printer. An optional Wi-Fi module is due to be added in the future.
For software, the Prusa Mini uses PrusaSlicer 2.2. It is based on Slic3r, an open-source program that takes 3D object files in STL, OBJ, AMF, or 3MF formats and converts them into G-code files, which essentially are the coded instructions for outputting the object on a 3D printer. Slic3r is an alternative to Cura, an open-source platform on which the slicing programs of numerous 3D printers we have reviewed are built, including models by Dremel, LulzBot, Monoprice, Ultimaker, and XYZprinting.
PrusaSlicer performs the same basic functions that Cura-based programs do, including loading objects—which are depicted to scale on a simulation of the printer’s build plate—editing them (resizing them, changing their position or orientation, adding multiple objects, and the like), setting the resolution and filament type, and adding supports or a brim. Then you “slice” the file, codifying the multiple thin layers that will be printed, one at a time, as the printer builds the object.
PrusaSlicer lets you select from a Simple, Advanced, or Expert interface, which each offers an increasingly wide range of settings to choose from. I liked the feel of the PrusaSlicer interface, and it let me do what I needed with it, with one exception. It wasn’t able to slice one object—a representation of the Apollo Command, Service, and Lunar Modules—that I have had no trouble slicing and printing with Cura-based programs. I received an error message that there was a problem with the file, something about blank layers, and was not able to slice it into a Gcode file.
Testing the Original Prusa Mini: Consistently Good Output
As the Original Prusa Mini is a totally open-frame printer with no walls, it’s important to keep children and pets away from it during printing. That also applies to materials like plastic wrap and paper, as well as anything else that could melt or burn on contact with the hot extruder. Fortunately, once a print job is finished, the extruder and build plate automatically cool down. Another plus is that the Prusa Mini is relatively quiet, which isn’t always the case with open-frame printers.
All told, I completed 11 prints with the Prusa Mini. These included many of our normal test objects, as well as several new ones commonly described as “stress tests” or “torture tests,” which are often used to test the ability of 3D printers to render various kinds of detail.
I also printed several of the test files provided on the USB key that came with the Prusa Mini, including a working nut-and-bolt combo and a whistle that indeed produces sound when you blow on it. Most were printed at the default 150-micron/Quality setting, with a few at the 200-micron setting, optimized for speed. I did not notice any quality difference between the resolutions, nor between objects printed on the textured versus the smooth build plate.
The print quality was uniformly above average. The Original Prusa Mini did very well in rendering fine detail on our stress-test objects, and output on our main geometric test object was among the best I have seen. It did particularly well in printing raised text, even at small sizes. None of the finished prints had any significant problems, and many showed no visible flaws.
A Simple, Yet Uncompromising, Budget 3D Printer
Manufacturers of under-$500 3D printers usually have to make some compromises to performance or quality to keep their prices low. Not so the Original Prusa Mini. It’s easy enough to assemble, has a good-size build area for its price, and can print with a variety of filament types. Most important: Once calibrated, it produces consistently high-quality prints with few visible blemishes.
Now, the Prusa Mini isn’t for everyone. Some newbies will be happier with a plug-and-play, fully assembled model like the Polaroid PlaySmart 3D Printer, and the first-layer calibration can be arduous. Parents and pet owners may prefer a closed-frame printer such as the FlashForge Finder. But once it’s up and running, the Prusa Mini is capable of churning out great-looking objects better than any budget model we have tested to date. It becomes our newest PCMag Editors’ Choice winner for budget 3D printers.
