Printed It: Parametric Hex Key Holder

Desktop 3D printing is an incredible technology to be sure, but it’s not a cure-all. If you’re interested in making something in large numbers, or if production speed is a concern, 3D printing probably isn’t what you’re looking for. But on the flip side, if you want to make a few highly specialized or customized objects, desktop 3D printing represents an absolute revolution in capability for the individual hacker and maker.

In our ongoing mission to prove that desktop 3D printing isn’t just a novelty, we keep a close eye out for printable objects which play to the strengths of the technology. You won’t find any benchmarks or dust collectors here; everything featured in Printed It is a bona fide practical object. An ideal entry into this series is something that you wouldn’t need to print more than a few times, isn’t easily sourced or made via traditional means, and if possible, offers some form of customization which makes it more suitable to the individual’s needs than what’s commercially available.

Not every object we feature hits all of these marks, but this parametric hex key holder designed by [Daniel Leitner] absolutely does. This object was created to address a problem that we imagine most Hackaday readers share: taming an ever-growing collection of hex keys. What’s more, this design is something of an open source success story. It’s an idea that passed through the hands of multiple community members, becoming more refined and functional as it went. Even if you don’t personally need to wrangle some unruly hex keys, this object is a fascinating look at how 3D printing and the community that has sprouted up around it is truly evolving the process of going from concept to execution.

Made-to-Order Design

Somewhere along the line it was decided that every kit, be it an entertainment center or a laser cutter, would include a handful of hex keys. So pretty soon you’re drowning in the things, but of course you never quite have the makings of a complete set and invariably you’ll have duplicates of certain popular sizes. Since folks like us have trouble getting rid of anything in the first place, they just end up filling some dark and dusty drawer until there’s enough of them that they start planning an insurrection.

To help quell the uprising, [Daniel] leveraged the parametric capabilities of OpenSCAD to create a fully custom holder for your collection of hex keys. By entering in the various sizes and number of hex keys you have into an array at the top of the script, his code will spit out a printable model that fits your exact specifications. So if for example you need to hold a half-dozen 2.5 mm hex keys, this design has got you covered.

In a particularly nice touch, the script will even deboss the sizes of the hex keys right into the holder so there’s no doubt about which one is which. While admittedly a minor detail, this is an excellent example of the power of OpenSCAD, and is something that would be difficult to recreate with more traditional CAD tools.

Refining the Concept

While he’s responsible for the parametric OpenSCAD code, [Daniel] didn’t actually come up with the original design for the hex key holder. That honor goes to [Alex Rich], who created a “static” version of the holder a couple of years back. That version was well suited for moving your store-bought hex key sets over to a slightly more ergonomic holder, but lacked any customization and relied on a printed (as in, on paper) label for the top to show which slot was for which key.

Render of original hex holder design.

That initial design was quite popular, and pretty soon [Alex] started getting requests for custom versions. He tried to accommodate the requests and put out different variations to the core design, but it was a losing battle. There’s simply too many permutations for one person to keep updating the design for each person’s scenario. He had put out the design because he thought others might find it interesting, not to take on a part-time job.

[Daniel] saw the situation and thought it would be a perfect application for OpenSCAD. He recreated the basics of the design: a disc-shaped holder with various sized openings around the periphery, but also made some critical improvements beyond the parametric aspect. For one, the original design required support material inside the groove, but the new OpenSCAD version uses an angled face on the top side to remove this requirement with no impact on functionality.

In other communities, this might be considered a “rip-off” and kick off some sort of flame war, but not here. [Alex] not only appreciated the work that went into the OpenSCAD version of his design, but now actively points it out to anyone who asks him for a custom version of the original holder.

Printing Your Own

Since this is a customizable design, the first step is opening it up in OpenSCAD and making your modifications at the top of the file. You can enter whatever sizes you wish, but be aware there doesn’t seem to be any error checking in place. So for example if you enter in a size of 2.2 mm instead of 2.5 mm, nothing is going to stop you. The code is also surprisingly complex, so don’t be surprised if it takes up to a minute or two for OpenSCAD to generate your STL.

Once you have your STL the design is a very easy print, and relatively fast. You can use higher layer heights to speed things up, but if you’re using the parametric version with the integrated sizes, the text might come out poorly. I printed it at 0.15 mm which struck a nice balance between surface detail and speed, and the holder finished in just under an hour and a half.

After printing you need to provide either a rubber band or a suitable sized O-ring to fit into the grove. In both the original and parametric versions of the holder, the holes for each key are made loose enough that they won’t be retained from friction alone. The tension from the rubber band or O-ring is what actually holds everything in, so that the grip of the holder doesn’t degrade over time like it would be if it just used tight-fitting holes. In practice I found that O-rings work better than the rubber bands, even though the only ones I could find locally are actually much thinner than what the design calls for. When I tried with the rubber bands the keys had a tendency to get stuck on insertion, but it will certainly work if you can’t find O-rings big enough.

Work with What You Have

Critics will say that the shape of this hex holder makes it uniquely suitable for traditional manufacturing: use a lathe to cut the O-ring grove into a piece of round stock, and then put it on the drill press to make the individual key holes. You’d lose the key sizes written on the side, but it would be faster to produce and much stronger than a piece of plastic. While all that’s true, we’re talking about thousands of dollars of equipment and the dedicated workshop to hold it all versus a cheap 3D printer in a hacker’s apartment.

The point isn’t that 3D printing is always the only, or even best, way to produce these designs. But it’s absolutely the most approachable and affordable way to do it, and goes a long way towards democratizing the creation of custom physical objects.

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