Counterfold Case

Howdy, wonderful people!

Why have one hinge on a lid when you can have six, right?!

Some years ago I played around with different approaches to a geometric mechanical model known broadly as a kaleidocycle, where a set of rigid elements connected by normal, single-axis hinges was able to endlessly turn inside-out. Such a fascinating mechanism, and I had long wondered if it would be possible to turn it into some kind of container. What if we just took a basic kaleidocycle model in a "flat" state, and projected some panels inwards to form a completely connected plane?

Well, it quickly becomes clear that it's really easy for parts to crash into each other and jam the motion up! But once those things are sorted out, the "lid" unfolds and, true to kaleidocyclic tradition, inverts itself so that the lid components point outwards instead, leaving a void in the middle, now formed from what were previously the outer walls.

The most impactful design decision at this point was to choose the position in which the lid would sit during printing, and it ended up being half-way through the motion between fully-open and fully-closed, with the main box body on its side. In any model, of course, there are lots of little design features that are the unseen heroes, and in this one it's the features that keep panels moving into the right spot and staying there despite shallow hinges and large ranges of movement. Those are the difference between a mechanism where moving parts could still get jammed up if it was held on just the right (or wrong) angle, and one where it's so smoothly reliable that you forget that it could be any other way!

Now, at this point the design diverges into two versions:

Complex Counterfold Case - the larger one, where the mechanism forms a lid on top of the case.

Streamlined Counterfold Case - the smaller one, where the mechanism surrounds the box body when closed.

Fundamentally, the mechanism is the same in each, but one container resides within the structure of the lid, while the other sits underneath it.

Now, one thing that is not obvious when picking up the box is how best to open it, so there are some small hints. The larger model has cutouts under two corners, and pulling those up simultaneously will fold the corners towards each other and open the lid smoothly. The smaller one has a cutout under one of the side panels, which serves the same purpose (but fits better with the much more compact vertical profile.)

(note on the multicoloured prints in the photos - I've just used the painting features that are in modern slicers - there's no need for a dedicated version of the model for this)

Print Description

This is an articulated model so take care that the first layer is nice and neat and that there aren't any print issues such as stringing or overextrusion that might bind moving parts together!

Optional Magnets

Magnets aren't at all necessary for this model, but they do make it a little more polished and make closing the lid nice and positive. If you do go with magnets, you'll need four of them, and they're our old favourite 6x3mm cylindrical magnets.

Print Dimensions

The larger version of the model occupies 207mm x 204mm on the print bed and is 114mm tall.

Supports Needed?

Not at all!  Designed for straightforward printing!

Scalability

This one should scale reasonably well, with the usual caveats about moving parts getting looser or tighter. Bear in mind, though, that the magnet mounting locations will scale, too!

I've printed the larger one at 60% scale and it turned out nicely!

Print Orientation

Both versions of the Counterfold Case print with the lid flat in a half-open state, and the main body of the box on its side.

Further Thoughts

Ah, so many design choices!

In this final version of the design one of the lid panels is fixed rigidly to the box body, but that wasn't originally the way it worked. Instead, the connection was hinged, but that made it much more awkward to close the lid, since holding the box body did not also hold firm one of the lid panels.

That was a pretty reasonable option to try, though, unlike another idea I did explore: replacing the body with a second lid mechanism! Not a terribly useful configuration, and unfortunately it doesn't really end up as "flat" as you might want from a container that unfolds. Still kind of fun, but not really any more novel than the Counterfold Case ended up being anyway :)

Happy printing!

xoxo
Sven.

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467 Counterfold Case