Getting Started with Puzzle Printing

Author: Aaron Siegel

3D printing can be a satisfying way to experience a wide range of mechanical puzzle designs. The learning curve is mild, and with a little practice, you'll be able to produce functional and attractive puzzles with consistently high quality.

This tutorial is designed to be accessible to readers with a broad range of 3D printing experience, including complete novices (or those who are pondering getting a 3D printer and are curious what it's all about, but haven't taken the plunge yet). It's focused on printing existing models from the Printable Puzzle Project library; modeling new designs is covered in a separate tutorial, Puzzle Modeling.

3D Printing Basics

There are several types of 3D printers on the market today. The most common, by far, are FDM ("Fused Deposition Modeling") printers, and they'll be the focus of this tutorial. (You might sometimes see the acronym FFF - "Fused Filament Fabrication" - used instead; it means the same thing.) FDM printers operate by heating a strand of plastic filament to a temperature of 200 °C or greater, then extruding the molten filament onto a smooth surface (the "print bed"), one layer at a time, so that it solidifies into the desired shape.

A 3D printer model is a file describing the shape of an object to be printed, most often an STL file. An STL file contains information defining the surface geometry of an object, but it does not contain detailed printer instructions, such as the resolution of the print, the filament temperature, or the desired interior density of the printed object. Those details are filled in by a slicer, a piece of software that translates an STL file into low-level printer instructions.

And that's really all you need to get started: a printer, some filament, an STL file, and slicer software. If all this is new to you, I'd suggest you take some time reading up on 3D printing basics before diving in to puzzle printing; there are numerous enthusiast sites such as with a seemingly bottomless amount of information.

If you're looking for specific printer or filament suggestions, you can find them on our Recommendations page.

Filament Types

There are many different types of filament on the market today. The most popular is PLA filament ("PolyLactic Acid"); it's easy to print with, non-toxic, biodegradable, and inexpensive. It's also available in an extremely wide variety of colors, as well as specialty varieties such as PLA filament infused with glitter or wood fiber. On the downside, PLA is fairly brittle and has low heat resistance; other materials, such as ABS, nylon, or carbon fiber filaments, are more durable.

For mechanical puzzles (and other hobbyist applications), the downsides of PLA aren't a terribly big deal, and for this reason I find it ideal. In fact, it's the only thing I print with! You are welcome to experiment with other materials, of course (and I'd be interested to know the results of those experiments), but after around two years of puzzle printing, I feel I haven't come close to exhausting the possibilities of PLA.

That being said: not all PLA filaments are equal, and poor-quality filament can be a source of much frustration. Choose carefully, and check out our Recommendations page for filaments that have proven success with puzzle printing.

The six pieces of Coffin's Half Hour puzzle, arranged for slicing in Slic3r

Half Hour, printed in Lavender PLA and fully assembled

Printing Your First Puzzle

For a first puzzle print, I suggest Half-Hour by Stewart Coffin. In addition to being a fine puzzle, it's very easy to print, with simple pieces that can tolerate printer imperfections.

To print it, first go to the Thingiverse page for Half-Hour, here:

Download the STL file coffin.half-hour.pieces-smaller.stl, load it into your slicer, and render ("slice") it for printing. The default settings in your slicer should work fine: Half-Hour is easy to print and should tolerate most settings. If you'd prefer to print the pieces one (or a few) at a time, your slicer software should provide options to split apart models and rearrange the components.

Then, just follow your 3D printer's instructions to print the rendered model. After some time (around 7 hours on my printer), you'll have a functional copy of Half-Hour. Enjoy!

This is a good time to mention an important principle. All puzzles on the Printable Puzzle Project are freely available and open source: anyone may download and print them for personal use. However, the puzzle designs and models are copyrighted. They're posted with the generous permission of their designers, and the designers retain all rights as copyright holders. Our non-commercial license allows for unlimited personal use, but strictly prohibits selling or otherwise monetizing any of the models or other work posted here.

A piece from Coffin's Quartet that is more challenging to print.

It's modeled in two separate components using "snap joints".

The components can be neatly snapped together after printing.

Snap Joints

Half Hour is a particularly simple model; each of its pieces can be printed directly as a single component. Many interlocking puzzles, however, have pieces that are more complex. For example, in the figures above, you can see one of the pieces from another Stewart Coffin design, Coffin's Quartet. No matter how this piece is rotated, some part of it will always extend over empty space - an overhang.

As discussed above, FDM printers operate by building objects in layers on a print bed, so overhangs create a challenge. One solution is to print using supports - temporary structures that provide a base of support for the overhanging components, which can be removed once the print is complete. Unfortunately, supports are not ideal for puzzle printing. They tend to leave visible scars on the surface of the object, which at best disturb the puzzle's appearance, and at worst interfere with the fit and render it inoperable.

This challenge is neatly addressed using "snap joints". Pieces with overhangs can be printed in multiple components, with connectors that snap together once the print is complete. This allows a very wide range of piece shapes to be printed, while ensuring that the pieces have a consistent, smooth finish. The pictures above illustrate how this works for Coffin's Quartet.

If you look closely, you can see a letter "B" stamped on the surface of the joint. There is a corresponding letter "B" stamped on the inside surface of the female joint, which is a bit harder to see in the photo. This makes it easy to determine which joints go together when printing a collection of pieces with many snap joints. In addition, the joints are tapered on one end, ensuring that they fit together in one orientation only, in order to make assembly of the puzzle as "foolproof" as feasible.

The snap joints in our puzzles are designed to be tight and to form a strong, permanent connection. Because the dimensional accuracy of printers varies (more on this below), you might find that some joints come out a bit too loose or too tight. Joints that are too tight can almost always be hammered or clamped into place, and joints that are too loose can be reinforced with a few drops of ordinary superglue. It's a good idea to keep a hammer and some glue on hand; the extra effort will be worth it!

Resizing Puzzles

You may occasionally wish to print a puzzle in a smaller or larger size than the one provided, and you might be tempted to use your slicer software's "resize" feature to do this. Don't do it! Resizing the puzzle in your slicer will, as a side effect, also resize the tolerances, making the puzzle fit tighter (if the size is reduced) or looser (if it's enlarged).

The recommended way to resize a puzzle is to re-render it at the desired size using OpenSCAD. This will alter the size of the puzzle while preserving the intended tolerances. For details on how to do this, refer to the Puzzle Modeling tutorial.

Which brings us to:

A Word on Tolerances

If puzzle pieces were printed with mathematically perfect dimensions, they wouldn't fit together at all, because the surface of a piece isn't perfectly smooth. In order to account for this, all of the puzzle piece surfaces are inset by a small amount, ensuring that there is some empty space between them so that they can slide smoothly together. This allowance is the tolerance of the puzzle pieces.

Tolerances are a tricky business: If they're too small, then the puzzle will be uncomfortably tight and difficult to operate. If they're too large, then the puzzle will be loose-fitting and won't hold its shape well. This is a particular challenge with 3D printing, because not all printers yield the same dimensional accuracy or smoothness of output. Even the brand of filament can make a noticeable difference in the fit of the puzzle.

We've taken pains to find tolerances that provide a good balance on most printers. For interlocking puzzles, our tolerances are generally calibrated to be slightly too tight. This is because 3D printed puzzles tend to loosen over time: with a little use, some of the roughness of the surface grinds away due to the natural motion of the pieces sliding together. Keep this in mind if your prints come out slightly too tight; try playing with them a bit, and they should loosen. (If they're so tight that the puzzle is difficult to operate, that's another story; the fit is probably not quite right for your printer. We love feedback, so if this happens, please report it to the PPP team.)

All of our models are generated from source code using OpenSCAD, with adjustable tolerances, so if you want to play around with different settings, you can generate new STL files from the OpenSCAD source. This requires a little more effort, though - see the Puzzle Modeling tutorial for details.

That's all! Head over to our Puzzle Index for some other great designs to print, or check out our other tutorials.