Latcher Bowl

Hey there, wonderful people!

I've been doing all sorts of latch-style things recently, but I've generally ended up with either threads or magnets involved, and I figured I'd see if I could get something working that just deformed the material itself. I'll stop short of saying "by using printed springs", though, for reasons that I'll get into momentarily! But the short story is that these stacking tubs rotate and click together, and likewise there's a lid that uses the same mechanism. So let's look at this mechanism!

Hmm, springs, springs. Springs are just great, as long as you're using the right material! PLA isn't necessarily that material, however, as it tends to end up deforming, especially when under sustained load, which posed a problem for this idea. I set a goal - use the springiness of the material to resist the process of latching and unlatching, but make sure the parts are back in a neutral, load-free state when actually latched.

Here's how it works: The bowls are stacked together, then twisted so that little wedges on the inside of the top of the bowl encounter the slotted bumpy prongs tucked away at the base. The wedge pushes the prong inwards, and the springy prong pushes back until the wedge clicks past and is trapped in the space between the two prongs. There should be just a little movement at this point, because the prongs should be completely relaxed again. Twisting the bowls apart again pushes the prong inwards, but from the inside this time.

The mechanism is relatively simple, but getting the right kind of dimensions was the bit that took time! The tension is driven by the angle of the bump on the prongs and the length and thickness of the prongs, and my early prototypes were multi-pronged monstrosities intended to just evaluate different configurations. That's one of the really fun aspects of prototyping this kind of thing, just not really knowing how things will perform, and waiting patiently* for the next prototype to finish!

(*mostly patiently. But I also cut down the model down to absolutely bare minimum needed to test the mechanism :D)

Print Description

This print relies on unhindered movement of small features that print directly on the bed, so make sure those are printing nice and neatly!

Print Dimensions

The Latcher Bowl occupies 108mm x 108mm on the print bed and is 92mm tall.

Supports Needed?

Not at all!  Designed for straightforward printing!

Scalability

Well now, that's a good question! Maybe! But the amount of deformation that the prongs will take before they are saved from more terror by the supportive barrier behind them is carefully aligned with the size of the wedge and the distance between the wedge and the prongs in the first place, so... maybe! It will be easy enough to test and see! :)

Print Orientation

The bowl and lid both print right-way-up, with the prong mechanism down.

Further Thoughts

Oh, there's one other aspect of the latch that I didn't mention! Now, obviously there are elements involved that stop the two parts pulling away from each other once the latch is engaged, or else the latch would not be very useful.

Those elements that lock against each other are angled such that, if you really pull the two parts apart with some force, they'll push the prongs in and release things much as if they were twisted.

An early version had a more "secure" set of faces that were far more aggressive in holding on, but all the force involved is directed straight into the prongs, and pulls directly against the layer lines, too! Like a cursed frogurt that contains potassium benzoate, that's bad*! So, the prongs now get pushed open rather than torn off.

There was also a version that just incorporated a separate rail that could engage and prevent pulling apart in a more robust way, to effectively completely decouple the latching and the holding-on-ing, but it made things much more complex, more prone to print issues, and most significantly it reduced the fidget-ability of the latch mechanism! And we can't have that, now :)

Happy printing (and fidgeting!)

xoxo

Sven.

(*apparently potassium benzoate isn't actually that bad after all)

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501 Latcher Bowl