Bandit Box

Howdy, wonderful people!

There are lots of ways to make mechanisms that have a bit of spring to them! Mechanical springs are the obvious thing that spring to mind (har har), but of course the Lodestone Latch Box mechanism used sets of attracting and repelling magnets to implement a spring too. But one thing I hadn't tried working with was rubber bands.

Ah, the Lodestone Latch Box! I love the latching mechanism, but it really would have been improved if unlatching also lifted the lid a little further. Magnets just weren't up to the task on that one, at least not without piling a whole bunch in there. But rubber bands, those things can hold quite a bit of energy! Could a rubber band be used both to implement a springy latch and to flip open a lid?

Actually, making a rubber band-powered latch wasn't too tricky. And a mechanism for springing open the lid wasn't too problematic either. However, getting them to exist at the same time was a much bigger conundrum! At one point the box was an upside-down print with a pointy base, but eventually it was wrangled into the form in the photos here, which prints in a more conventional way, and requires just one single rubber band for both the latch and the lid!

With the lid open, the rubber band is looped across the front of the box, to pull the latch in. There's a pivot point part-way up the box, so the bottom panel now pushes out - push that inwards to open the latch!

The rubber band loops across the back and is held out from the back wall by the box sides, which protrude past the back of the box for this very purpose.

So, when the lid closes, it pushes the rubber band inwards, storing vital energy for springiness! The part of the lid that contacts the rubber band is inset somewhat so that the rubber band doesn't get overly pinched as it is drawn forward.

And then when the lid is pushed down firmly the latch moves forward and then snaps back, teeth in the lid engaging with the inside of the latch. Press the lower latch panel to spring it back open again, with the power of rubber band technology!

Some thoughts about friction!

When the box is first printed, the lid will probably jam up against the latch a bit, because layer lines are grating against layer lines. The teeth on the lid come to a point so that the contact area is minimised, which did help quite a bit, but the layer lines still do like to grab on to each other.

I experimented with a few different angles, but steepening the angle of incidence really only achieved so much. Fortunately, those layer lines will wear down quickly, depending on the material in use! Or you can just sand it a little like I did, to speed up that process.

Choosing a rubber band

You really don't need the rubber band to be under a lot of tension! The ones I've used are relatively relaxed, but it's still enough to pop the lid right open. Tighter rubber bands aren't really going to make things work better, but will put more outward force on the lid hinge. Choose wisely! :)

Print Description

This is an articulated model so make sure your first layer is nice and neat, and that there aren't any print issues like stringing or overextrusion that might bind moving parts together!

Print Dimensions

The Bandit Box occupies 70mm x 157mm on the print bed and is 60mm tall.

Supports Needed?

Not at all!  Designed for straightforward printing!

Scalability

This one should scale quite well! The tolerances are generous enough that it should scale down reasonably happily before things get too tight, and the hinges are large enough that they shouldn't get too loose as it scales up. You'll need to find appropriate rubber bands, though! :)

Print Orientation

The Bandit Box prints on its base, with the lid folded open onto the bed.

Further Thoughts

Okay, I tested the scaling! The orange print is 100% scale. The little one is 60%, and the big one is somewhere around 200% - thanks to Courtney at Filament Stories for printing that one up on the Prusa XL!

Happy stretchy printing!

xoxo

Sven.

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498 Bandit Box