Springlatch Box

Howdy, wonderful people!

I do love a nice latching mechanism! I could never get tired of exploring different ways to keep lids closed! But a big part of the appeal isn't so much the effectiveness of the latch (they're all generally pretty good, after all) but the tactile experience of closing and opening the thing. This one has a nice, satisfying click when the latch snaps into place, and in fact the working name for it was something like "Clickety Box". I wasn't convinced that I hadn't already used that name, though :P

So, let's talk springs! I am generally hesitant to incorporate printed springs into things, though by that I really just mean that I have to convince myself there's an actual reason to do so. I'm also conscious of the relative fragility of the materials we work with, and how easily a spring can instead become a piece of permanently bent plastic, so those things need to factor into the design. So, where's the spring in the Springlatch Box? The classic wavy-line spring design is visible front-and-centre on the edge of the lid, and it's the element that connects the latch to the lid body.

When the latch button is pushed in, the spring is twisted (and presumably both compressed and extended in different parts) and pushes the latch back out. As the lid is closed, the latch encounters guide rails that push it backwards until the lid reaches the closed position and the latch pins slip off the end of the rails and allow the latch button to snap outwards. Likewise, the lid won't open until the button is pressed inwards so that the pins clear those rails.

An important design element in all this is that when the lid is latched closed the spring is at rest. The spring is only loaded when the latch is being pushed in, during the actual opening and closing process. So, there's no risk of the spring becoming deformed simply by being held with load for long periods. There are a bunch of other little features of the design that are needed to ensure the latching works effectively, and those serve largely to constrain the motion of the parts as the lid closes. Without them, the spring would push the lid out of place and reduce the effectiveness of the latch itself!

Print Description 

The Springlatch Box is an articulated model, so make sure your first layer is nice and neat, and watch out for print quality issues like overextrusion or stringing that might bind moving parts together.

Print Dimensions

The Springlatch Box occupies 76mm x 163mm on the print bed and is 56mm tall.

Supports Needed?

Not at all!  Designed for straightforward printing!

Scalability

There's nothing specific to stop this being scaled up or down, but the usual caveats apply about scaled tolerances making things too tight or too loose!

Print Orientation

Prints with the lid open and outside-down on the print bed.

Further Thoughts

My first bit of inspiration after making this latch design was that it would work really neatly as a ratchet mechanism, and that promptly turned into the Extraplanetary Geared Stand. I still like the idea of a proper ratchet system, though, especially since I do have an abandoned design for a box with a ratcheting lid that would work much better than whatever approach I took at the time! :)

Happy printing!

xoxo

Sven.

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479 Springlatch Box