This article introduces and explores the new Prusa Core One printer. It includes a number of methods to increase this printer's accuracy and usefulness. Some printable 3D resources are included, including a Web camera mount to provide a local-network, full color, video frame rate printing monitor, to replace the Prusa Buddy3D camera.

This article describes the Prusa Core One from a user perspective. I have no connection with Prusa, no editorial constraints, and some personal preferences having to do with privacy and independence.

This article assumes you have a working Prusa Core One, either a factory-built machine or a completed kit. This article goes beyond the instructions provided by Prusa and offers some configuration and tuning advice not found elsewhere.

Although this article's focus is the Prusa Core One, many of its methods apply to other Prusa printers.

This article is intended as a resource archive for a video yet to be released.

Let's get started!

As delivered, either factory-built or user-assembled, this printer needs certain alignments for best performance, some of which aren't very well documented. This section provides a Z-axis (vertical) alignment method to level the print bed.

Figure 1: Pathologically Misaligned Print Bed

Figure 1 shows a print bed with greatly exaggerated misalignment, just to make a point — if the print bed isn't properly aligned or "leveled", many other things will go wrong. On delivery, many Prusa printers, especially those assembled by the recipient, will have misaligned print beds.

It's important to say the printer will automatically detect and if necessary correct small Z axis misalignments, at the start of each print. This special procedure is meant only for newly assembled / arrived printers, where a Z misalignment may need special attention, to avoid component wear and stress.

Here's the procedure: the Prusa Core One print bed is supported by three threaded shafts, each connected to a stepper motor. The stepper motors operate synchronously, rotating the threaded shafts during printing, so that the bed remains level at all vertical positions — but this is only true if the bed has been properly leveled in advance. In this section we'll make sure the bed is level.

Here are the steps to align the print bed:

• Move the print bed to its lowest position. This is accomplished using the Prusa Core One control menu:
• Start at the main menu control icon
• Move Axis
• Move Z
• Press the control knob to activate motion, so the current position is printed in red
• Rotate the control knob to move the print bed to its lowest position.
• As the print bed arrives at its lowest position, this will likely be accompanied by a grinding or clicking sound — this is harmless but at that point, stop the motion inputs.
• Either activate the "Disable motors" command, or turn off the printer. The latter choice is simpler and safer.
• Manually rotate each of the three threaded shafts counterclockwise (as seen from above) to move the print bed to its lowest position:
  
  Figure 2: Shaft Rotation to Level Print Bed

• This procedure should level the print surface:
  

  Figure 3: Level Print Bed (click for full-size)

  The Prusa Core One is designed so that, when the three shafts have been rotated counterclockwise to the degree possible with power off, the print bed will be level. Then, during printing, because the print bed motors are synchronized with each other, the print bed will remain level at all other positions.

After the printer has been given an initial alignment and placed in service, it automatically detects and corrects Z misalignments at the start of each print, so this procedure need only be performed once.

NOTE: Before we get started, let me say that XY axis alignment, and belt tensioning (the next topic), should be managed independently. I say this because in online forums, many Prusa printer owners seem to think they can solve an XY axis problem by changing belt tensions. Don't do this — for correct printer operation, these issues must be managed separately.

Unlike Z misalignments, which the printer can automatically correct, XY misalignments require either professional or user intervention. This section explains how to manually correct XY misalignments.

The Prusa Core One uses the so-called "Core XY" scheme, in which the print head's X (left/right) and Y (toward/away) positions are controlled by stationary motors and a system of belts and pulleys. For accurate motions and printing, this scheme requires that the X and Y axes be separated by exactly 90°, so that X motions have no effect on the Y dimension and vice versa.

One clue that the X and Y dimensions aren't properly aligned is something called "Print skew":

Figure 4: Print Skew (greatly exaggerated)

The effect seen in Figure 4 results from the fact that the printer's X and Y axes aren't separated by exactly 90°. This can have many undesirable effects on 3D printing, as well as cause the Prusa Core One to fail its Y axis motion test:

Figure 5: Prusa Core One Y-axis motion test failure

The remedy for this issue is to tune the relationship between the X and Y axes so they are "orthogonal," meaning separated by exactly 90°. Unlike the Z axis adjustment explained above, correcting this misalignment requires applying a small amount of force to the Core XY mechanism — very carefully, minimal necessary force, and with intermediate tests after each adjustment. Here is the procedure:

• First, cover the printer's fragile bed heater with a print surface or cardboard sheet to protect it from dropped tools and other accidents.
• Next, contrary to much online advice, Do not loosen the belt tensioners in preparation. This remedy is most effective when carried out with normal belt tensions. If you loosen the belts to perform this procedure, then tighten the belts again, you will lose the accuracy of the outcome.
• Turn off the printer — no power is needed for this procedure, and removing power will reduce the possibility of unintended control activation.
• Manually move the X carriage fully to the back of the printer and center the print head (with printer power off, this requires very little effort):
  

  Figure 6: X carriage and print head correctly positioned (click for full-size)

• Now press the left and right ends of the X carriage against the provided stops, toward the back of the printer, as shown:
  
  Figure 7: X Carriage Clearance Test

• In a properly adjusted Core XY carriage, the amount of movement, and the required force, on each end of the X carriage should be equal, without a larger amount of motion at one end or the other. And if this is already true, go no further, don't make any more adjustments.
• If instead there is a larger gap at one end of the X carriage than the other, and if you feel confident in your technical skills, you may choose to adjust the X carriage so the two ends have the same gap at the motion stops.
• NOTE: If you have never done this sort of thing before, or if you don't feel confident in your ability to carry out this procedure, you can always hire a professional to perform this adjustment for you. Don't forge ahead without an understanding of the process and the possible outcomes.
• The purpose of the next step is to gently and carefully bend the X carriage mounting brackets so the angle between the X and Y dimensions is exactly 90°.
• Make note of the end of the X carriage that has the largest gap, and create a gap with any convenient tool behind the opposite end, as shown here:
  

  Figure 8: X carriage adjustment setup (click for full-size)

• Gently apply some force to the free end of the X carriage as shown in Figure 8. Don't apply too much force. And remember that your printer's X carriage might need an adjustment opposite that shown in Figure 8, in which case the adjustment and tool ends of the X carriage as shown in Figure 8 should be reversed.
• Remove the tool shown in Figure 8 and repeat the clearance test shown above in Figure 7 to see whether the two ends of the X carriage have the same gap between themselves and the stops. The goal is to give the ends of the X carriage the same clearance from the stops, or in other words, to assure that the X carriage is at exactly 90° with respect to the Y axis rails at each side.
• Repeat the adjustment shown in Figure 8, and the test from Figure 7, as required to make the right and left X carriage gaps equal.
• A successful adjustment will result in the same amount of Y-axis clearance at each end of the X carriage, and when this is so, the printer should pass its Y motion test, and X/Y axis test prints should look like this:
  

  Figure 9: Successful Core XY alignment test print (compare to Figure 4 above)

Figure 10: Core XY Belt Layout (click for full-size)

Overview

The Prusa Core One relies on a system of belts and pulleys to move the print head in the X (left/right) and Y (near/far) axes. The belts are visible at the right and left sides of Figure 10 above.

As it turns out, belt tensioning is critical to successful operation of the printer, and unlike Z axis misalignments, the printer cannot automatically perform this procedure. Indeed, of the remedies listed in this article, belt tensioning is the most important.

Here's an outline of the belt tensioning method:

• Turn off the printer.
• Move the print head to the position shown in Figure 10 — all the way to the rear, and centered between left and right.
• Gently pluck the belts like guitar strings, at the center of their long spans at the left and right, while measuring their frequency.
• While monitoring the belts' frequencies (see below), with an Allen wrench carefully adjust the belt tensions using the tensioners marked in Figure 11:
  

  Figure 11: Core XY Belt Tensioner Locations (click for full-size)

• Use a frequency meter (see below) to measure the frequency of the plucked belts.
• Interactively pluck the belts and adjust their tensions as explained above, until both belts are tuned as close to 85 Hz as is practical.
• It's important that both belts be tuned to the same frequency, in any case within a few Hz of each other, and as near to 85 Hz as practical.
• NOTE: a number of Prusa Core One users report that their belt tensioners failed after multiple uses, making further belt adjustments impossible. I had the same experience, so I designed a printable tensioner upgrade, fully described below — look for "Belt Tensioner Upgrade" later in this article.

At this point my readers will ask, "Wait ... how do I measure 85 Hz?" Here are some available methods:

• The cellphone-compatible Prusa Mobile App, which includes a marginally functional frequency measuring method (Android link | IPhone link). This is the least usable method.
• An Android app called "Spectroid" (download link), much superior to the Prusa method, only available on the Android platform.
• Other frequency measuring utilities are available for the IPhone platform, which unfortunately I cannot test.

But wait ... I provide a:

Test Signal Generator

To evaluate a cellphone frequency-detecting app in advance of trying to tune your printer's Core XY belts, here is a signal generator that provides a reliable 85 Hz signal for testing:

| | Gain: 50

• Press the Start/Stop button at the left and move your cellphone near your computer's speakers to pick up the signal.
• Adjust the speaker gain as required to make the signal audible, but without overloading your computer's audio system.
• Use this test signal to learn how to use your chosen frequency-measuring app in advance of actually trying to tune your printer's belts.

Frequency Measuring App Evaluation

Again, the Prusa Mobile app includes a way to measure the belt frequency, but it's not very good. It may take an unconscionably long time to respond to signals, meanwhile telling you that:

Figure 12: Prusa Mobile App Typical Display

A warning — don't assume that the Prusa Mobile app is providing correct information. If you assume it's accurate and expect it to respond in a timely way, you may overtighten a belt, with numerous consequences, all of them bad. Apropos, in early tests I trusted this frequency gauge, overtightened one of the belt tensioners and stripped it — see below for the full story.

By contrast, here is the Spectroid app display under the same circumstances, which responds instantly:

Figure 13: Spectroid (Android) Typical Display

Much better.

A Traditional Method

Let me suggest one more method, which won't be practical for everyone. If your computer has a quality sound system with the ability to play low-frequency sounds and is able to play 85 Hz clearly, without distortion and with enough volume, it should be possible to play the above test signal near the printer and match its frequency "by ear" while tuning the printer's belts. This is how an orchestra tunes its instruments, how a piano technician tunes a piano, and how groups of people sang the same note before modern times.

Okay, this is somewhat out of date, but in the right circumstances it would work.

In a nice symmetry, many 3D printer problems can be fixed by using the printer to create new parts, certainly true for this printer. Here are some online resources:

• Prusa Core One printable parts — the linked page lists a number of free downloads: a complete set of parts, or parts tuned for different print filaments, or parts by category.

It's desirable to print certain spare parts in advance of possible printer difficulties, after which it may not be possible to use the printer to create new parts. For example, in early experiments I stripped one of my belt tensioners (which turns out the be a common issue — see the section below for a better, user-printable replacement tensioner). Then, in a classic Catch-22, to print a replacement tensioner, I had to temporarily tension the printer's belt with baling wire:

Figure 14: Jury-rigged belt tensioner (click for full size)

So the moral of the story is — print spare parts before they're needed. And keep some baling wire handy, just in case.

Prusa offers a camera named "Buddy3D" for the Core One, but it has a number of drawbacks:

• Unless there is more light available than is typical for the Core One print volume, the camera provides monochrome images.
• The camera updates its image only once every ten seconds.
• Without an Internet connection, the camera stops working.
• Use of the camera requires a Prusa Connect account.

I think Prusa is a terrific company that has made many contributions to 3D printing over the years, but when I hear they require a Prusa account to use their camera, I want to consider a different one — and this section provides it.

The Basics

This project uses a 3D printed camera mount, some magnets, and an inexpensive color camera.

WARNING: This project relies on small magnets, magnets that pose a serious danger if ingested, as explained here. If you have young children in your household, keep firm control over the magnets when they're not attached to the camera mount. Don't let young children play with them.

The 3D printed mount looks like this:

Figure 15: 3D printable camera mount as rendered by Blender: without camera | with camera

Here's a list of resources / links for the camera mount:

• A SolveSpace design file for the mount, for those who need to customize the design, perhaps for a different camera.
• A printable STL file for the mount, suitable for the Yi camera listed below.
• A Prusa Slicer file containing the mount, with appropriate settings for ABS printing on the Prusa Core One.
• NOTE: If you create your own Prusa Slicer profile for this project, be sure to enable supports, like this:
  
  Figure 16: Prusa Slicer print configration with organic supports (click for full-size)

• Neodymium magnets, length 27mm, diameter 6mm, Amazon link, need 6.
• A small inexpensive camera, manufacturer Yi, Amazon link.
• A micro-USB to USB-C adaptor cable to power the camera from the printer, Amazon link.

NOTE: All these links will become invalid over time. I hope I have provided enough detail so the items can be located anyway.

Using Spring 2025 prices, this camera setup costs about US$42.00 altogether, only because one cannot buy just six magnets. This is slightly more expensive than Prusa's Buddy3D camera.

The Yi camera has a micro-USB connector, but the Prusa Core One has a USB-C power connector, so an adaptor cable is included in the above list, to use printer power for the camera.

Use of ABS filament is probably not required. I normally use ABS for durable parts that need to tolerate elevated temperatures, but I haven't tested other filament types, some of which may work correctly in this project.

Setup Instructions

When the above parts list is complete and the mount has been printed, take these steps:

• Slide six neodymium magnets into the slots provided in the 3D printed mount. Make sure all the magnets are inserted with the same polarity, i.e. the magnets should have either their North or South poles all pointing toward the center of the mount.

• NOTE: to compare the polarity of two magnets, place one magnet alongside another.

  • If the magnets resist being brought together, their polarities are the same.
  • If they snap together, their polarities are opposite.

Figure 17: Mount with installed magnets
• Remove the Yi camera from its tabletop support.
• Snap the Yi camera into the gripping fingers on the front face of the mount.

Figure 18: Mount with magnets and Yi camera
• Here is the camera mount, correctly positioned at the front upper left interior of the Prusa Core One enclosure:

Figure 19: Camera Mount in Service
• Using these instructions, route the USB adaptor cable from the Prusa Core One's USB-C power outlet to the upper left inside location where the Buddy3D camera would normally go.
• Connect the USB-C end of the adaptor cable to the Prusa Core One USB-C power connector.
• Connect the Micro-USB end of the adaptor cable to the Yi camera.
• Check for clearance and cable routing, then position the camera mount near the printer's upper left inside corner and release it.
• Make sure the mount is located symmetrically in its corner and firmly gripped by the magnets. Rotate the mount to be sure.
• With printer power off, move the print head to position Y = 0, X = 0 (the position nearest the camera) to make sure there is no collision possibility between the camera and the print head.
• Power up the printer and test the camera's wireless network connection. Make sure you have a clear picture of the print bed.
• To maximize the camera's usefulness, set the chamber light brightness to 50% or higher and disable dimming. Use this command sequence from the printer's main menu:
  • Settings
  • User Interface
  • Chamber Lights 50-100%
  • Chamber Dimming Off

Home Assistant Compatibility

The little camera described above is compatible with Home Assistant, a free, powerful home automation scheme. Among many other things, this software allows these little cameras to display a normal TV frame rate, which otherwise might provide a sequence of still pictures, not very useful.

Third Party Camera Firmware

Without any changes and like every modern TV camera, the above-described Yi camera is over-reliant on company resources and connections. But a first-rate, open-source, third-party project solves this issue for this very popular camera, so it no longer phones home — here's a link. If you acquire the same camera model as that listed in the Amazon ad, its firmware prefix should be y211ga, usable as a search string at the linked firmware site.

Or perhaps you have located some other small, inexpensive security camera that, with no changes, doesn't try to phone home. If you have, please tell me about it at my message page. This isn't likely, but anything is possible.

Here are some recommendations for 3D design software and the best slicer to use with the Prusa Core One.

CAD/CAM Design

Some of my readers know I've created a few videos about SolveSpace (example), a free, open-source, multi-platform computer design program. I recommend it for students and for those who prefer open-source programs over the alternatives. Here's the camera mount described above, as shown by SolveSpace, where it was designed:

Figure 20: Camera Mount design in SolveSpace (click for full-size)

Many alternatives to SolveSpace exist, but most are either too buggy and hard to use (FreeCAD), or they own both you and your projects (Fusion 360). SolveSpace has a rather steep learning curve and is missing some features many people regard as important (like the ability to create numeric dimensioning variables), but it's both free and pretty good. It's more than adequate for projects like those in this article.

Best Slicer Program

In my opinion, the best slicer program for the Prusa Core One is created by Prusa, named PrusaSlicer. The big advantage of PrusaSlicer is that it knows about the Prusa Core One and includes profiles for many filament types, with parameters tuned specifically for the Prusa Core One. This is a huge advantage over the common, time-consuming practice of tuning a slicer program to accommodate an unknown printer and a 3D printing filament of uncertain properties.

Another PrusaSlicer advantage has to do with print speed. Without inside knowledge of a printer's mechanical properties, a slicer program isn't likely to know how to balance print speed and quality. But PrusaSlicer understands the Prusa Core One intimately and has been extensively tested in order to maximize performance and print quality.

This section describes some of my magnet-related projects — projects where 3D printed parts are dynamically assembled by modern, inexpensive, high-powered magnets.

WARNING: If you have young children in your household, I recommend that you pass up these magnet projects, because young children may swallow small magnets, which can have serious, even fatal, health consequences as described here. A quote from the linked article: "Tiny magnets, like the ones found in building sets and other toys, can cause death in kids if more than one is swallowed. The U.S. Consumer Product Safety Commission (CPSC) has verified the death of a 20-month-old and at least 19 other small children being injured and requiring surgery."

These projects rely on inexpensile neodymium magnets, 27mm long, 6mm in diameter. Here's an Amazon link (2025.07.18), but don't be surprised if this link become invalid in time and you have to search for them.

The basic idea behind these projects is that you 3D print individual parts of a geometric object, add some inexpensive neodymium magnets to the edges of the parts, then the finished object is held together by the force of magnets. And in some cases the printed parts literally fly together under the force of magnetism. Here's a step-by-step example:

• Design one surface of a multi-sided geometric object, making sure to include mounting points for magnets. Here's a SolveSpace design image for one surface of a small cube (source listed below):



Figure 21: Cube Face Design in SolveSpace (click for full-size)

• 3D print as many copies of the basic design as the object requires:



Figure 22: Cube Face Design as shown in Blender (click for full-size)

• Add magnets to each part, remembering to keep the magnetic poles consistent — either North-pole counterclockwise, or the reverse, but consistently across all the parts:



Figure 23: Cube Face Design with Magnets, as shown in Blender (click for full-size)

• Here are real-world images of the small cube project, from individual parts with magnets in place, to fully assembled:



Figure 24: Cube Assembly Sequence, as shown in Reality (click for full-size)

• Again, remember about these projects that the magnets must be all polarity-aligned, either North or South poles arranged in a circle, or the reverse, but all magnets and all parts the same:



Figure 25: Magnet Polarity Test (click for full-size)

• HINT: Use this trick to compare magnets: if you try to press one bar magnet against another and you feel resistance, this tells you the magnets have the same polarity. If the magnets snap together, they have opposite polarities.

Here are some of my magnet-based projects, with SolveSpace design and printable STL files:

• Tetrahedron (4-sided object): SolveSpace / STL. Four sides, each with 3 magnets: 12 magnets.
• Small cube (shown above): SolveSpace / STL. Six sides, each with 4 magnets: 24 magnets.
• Large cube: SolveSpace / STL. Six sides, each with 8 magnets: 48 magnets.
• Dodecahedron (12-sided object): SolveSpace / STL. Twelve sides, each with five magnets: 60 magnets.
• Icosahedron (20-sided object): SolveSpace / STL. Twenty sides, each with 3 magnets: 60 magnets. This variation is a work in progress.

This section shows multi-sided objects that assemble with simple mechanical fasteners instead of magnets. These weigh and cost less than magnet projects, and they're safe for young children. The fastener I designed, used in all versions of the project, looks and works like this:

Figure 26: Mechanical fastener cube video

The basic idea of this symmetrical fastener scheme is that one need design only one face of a multi-face object, print as many copies as there are faces in the object, then assemble the faces. In the above cube video, I only needed to design a single face, after which I printed six copies. For the dodecahedron listed below, I designed one face, then printed 12 copies.

For various reasons and unlike other projects shown here, these projects rely on (a) the Python cadquery library, and (b) CQ-editor, an interactive cadquery graphics development editor. Developing these mechanical fasteners requires a lot of interaction and tuning, so an editor with graphic feedback is esssential.

The projects listed below are scalable without losing proportions, using a single variable. Normally one sets Python script parameters, then generates some test STL results, then examines the STL results in a graphic environment like Blender, then finally, 3D prints some actual parts.

• Cube: Python source (GPL licensed) / STL. This project is shown in the above video. To build the cube, one must 3D print six polygons, then assemble them using their mechanical fasteners.

• Dodecahedron: Python source (GPL licensed) / STL. This project creates a model of a classic Roman-era dodecahedron whose original purpose no one has figured out. Here's a reference. Only about 130 are known to exist, all built between the second and fourth centuries CE.

  To build this project, one must 3D print 12 polygons, then assemble them into their final form. This model optionally supports (and generates) vertex pegs, one of the distinctive features of the original Roman dodecahedrons.

  During development work on this project, I tried 3D printing the entire dodecahedron in one go, but because of the object's shape, it wasn't possible to print it without distortions and failures caused by overhangs. So I started over, printing 12 polygons and 20 decorative pegs separately, then assembling them. Because each polygon face lay flat on the print surface instead of being suspended in midair, printing issues were resolved.

  Here's what this project would look like, in a perfect world, with perfect 3D printers:

  Figure 27: Mechanical fastener Roman dodecahedron video

  This video was rendered by Blender, after a lot of fine tuning. An actual 3D print won't look remotely like this, it's only meant to show the basic idea.

In this section I list some of my (non-magnet) 3D printing projects, each with SolveSpace design files, printable STL files, and instructions.

General Project Source Files (SolveSpace and STL)

• 3D calibration test cube (SolveSpace / STL) — a classic 3D printer calibration aid, 20mm per side, with printed labels showing the cardinal dimensions X, Y and Z. For the labels, users will need to specify a locally available TrueType font, which for licensing reasons is not included in the source file.
• Aperiodic Tile version 1 (SolveSpace / STL) — This is a printable aperiodic tile as explained in this Scientific American article. Unlike Spectre below, this aperiodic tile version requires that the tile's mirror image be used at times. In this SolveSpace design, three hexagons are constructed, then the perimeter of the tile is created using coordinates provided by the hexagons. Click here for an image of the key sketch. Notice that the majority of the lines are construction lines, meaning lines that provide dimensioning/geometry but don't become part of the exported sketch.
• Aperiodic Tile version 2, i.e. Spectre (SolveSpace / STL) — this aperiodic tile model does away with the requirement for a mirror image of the pattern. Many have argued that this is the only true aperiodic tile design. See An aperiodic monotile for a full explanation. Click here for an image of the key sketch.
• Bike mirror mount (SolveSpace / STL). This is the flexible mirror mount fully described at this link.
• Cup, 400ml (SolveSpace / STL). This is a relatively simple, useful cup design that shows a few intermediate to advanced methods to accomplish its design. Like the calibration cube listed above, because of a capacity label printed at the bottom of the cup, this project also requires specifying a locally available TrueType font.
• Cup, Advanced Design, 400ml (SolveSpace / STL). This is a more practical cup that goes beyond a simple tutorial design.
• Metric M10 size threaded bolt (SolveSpace / STL). This design creates a working, practical Metric bolt of M10 size. This SolveSpace design file can be rescaled for other Imperial and Metric hardware sizes. It uses the SolveSpace helix feature and some careful dimensioning to make a practical bolt correctly sized to mate with a 3D printed nut (see below) or a metal nut of the same size.
• Metric M10 size nut (SolveSpace / STL). This project correctly interacts with the bolt listed above, or with metal hardware of the same size. As with the bolt listed above, this nut can be rescaled as required for other Imperial and Metric sizes.
• Helical Gear (SolveSpace / STL). An exercise in advanced gear design. Click here to see the primary sketch. Click here to see a Blender view of the meshed gears.

Special Projects and Resources

In this section I list projects based on Python and the CadQuery library. These projects require that Python and CadQuery be installed on your machine.

• BoxBuilder: Python source (GPL licensed) / example_box.stl / example_cover.stl

  

  Figure 28: BoxBuilder Example Result (click for full-size)

  The Boxbuilder Python source includes clearly named dimension variables for project wall thickness, box width, height, depth and corner radius. Because this program creates a cover as well as a box, the cover's dimensions are defined by the box dimensions except for a cover edge height variable and a clearance variable that adjusts the tightness of fit between the box and the cover. To use this program:

  • Edit the source — change the file output name if desired, and set dimension variables to meet your requirements.
  • Run the program — the printable STL files will be saved in the box builder's program directory.
  • Print the resulting STL files.

  In my build tests for this project, I printed using ABS filament on the Prusa Core One, but other printers and filament materials may require a change in the program's fit tightness variable. Remember that the fit tightness variable only changes the cover's dimensions, not that of the box, so if a change is needed, only the cover would need to be reprinted.

• Belt Tensioner Upgrade: Python source (GPL licensed) / SolveSpace Dimensions Worksheet / Belt Tensioner STL

  Disclaimer: Because this project involves hardware changes to your printer, and because people's mechanical skills vary widely, I accept no responsibility for bad outcomes or voided warranties — or anything else I haven't thought of.

  Since this printer's introduction, a number of reports have appeared in which a belt tensioner stripped out and became unusable during normal calibration actions. A close look at the original tensioner shows why — the factory-supplied plastic tensioner relies on an internal metal square nut to carry the belt tension load and screw turning forces as well (below, left). But because the tensioner is plastic and because belt tuning forces are relatively high, printer owners sometimes report that the square nut has begun to spin freely within the plastic part, making further calibration impossible. I had this experience along with many other printer owners.

  This project replaces the factory tensioner — and the square nut — with a redesigned part that uses a threaded brass insert, much less likely to fail under load (below, right).

  

  Figure 29: Belt Tensioner Alternatives (square nut versus brass insert) (click for full-size)

  Here are some details:

  I used the SolveSpace dimensions worksheet listed above to design the part and get detailed dimension information for use by the Python/CadQuery program, which generates the replacement part.

  To use the replacement part:

  • Download and print the STL file listed above, one or two prints depending on your needs (I recommend replacing both tensioners).
  • Be sure to use a strong, high-temperature filament for this part — ABS or a similar type. Don't use PLA — it can't stand the forces involved, and the print chamber can get pretty hot as well.
  • Heat-press an M3 x 8mm x 5mm brass threaded insert into each part:
  

  Figure 30: Replacement tensioners with brass inserts installed (click for full-size)

  • Replace the original tensioners with this part. This part uses the original tensioner's associated hardware without changes.
  • Retune the printer's belts as explained earlier in this article.

  This replacement has many advantages over the original. Apart from being much less susceptible to stripping out, it tracks the user's fine adjustments more accurately — compared to the orignal, whose square nut, when it wasn't stripping out, would turn a bit on each direction reversal before responding to the user's intentions.

• Filament Reel Holder: Python source (GPL licensed) / reel holder STL file / cover STL file

  

  Figure 31: Filament Reel Holder Body and Cover (click for full-size)

  This project builds a filament reel enclosure to prevent moisture absorption while printing is under way. Many filament types (TPU and nylon to name two) are very hygroscopic (prone to absorb moisture), and even after advance dessication, such filaments will absorb moisture from the environment while printing is underway. This project helps guard against that possibility.

  Inside the enclosure, the filament reel spins freely on an internal axle, and a small opening at the top guides the filament to the printer.

  To change this project's dimensions, edit the source and change the clearly named variables. I include these control variables because not all filament reels have the same dimensions (the defaults are set for Hatchbox filament reels). But larger filament reels may exceed the printing size of the Prusa Core One. Even with the Hatchbox reel defaults, printing this project requires nearly every square millimeter of the printer's X and Y dimensions.

  

  Figure 32: Filament Reel Container size in Prusa Slicer (click for full-size)

  To use the reel holder:

  • Place the reel holder at the right side of the Prusa Core One, adjacent to the machine's default reel axle.
  • Remove the desired filament from its moisture-free storage location and place it adjacent to the reel holder.
  • Pass the filament's free end through the port located at the top of the reel holder's main body and into the Prusa Core One's filament tube.
  • Now place the filament reel onto the reel holder's internal axle
  • To protect your filament from moisture during printing, close the reel holder with the provided cover.
  • Position the reel holder to minimize friction along the filament path.

  It would be nice to print this project using a transparent filament, which I'm told now exists, so the reel's motion could be observed without opening the enclosure.

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