Secret Heart box
by EricYoung, published
Uploaded a second version (all STL's are in the zip file at the bottom). It has thinner walls around the pivot and can only use 6mm Diameter x 3mm Thick cylindrical magnets to stay in position. Otherwise it's basically the same as the first version
While watching The Illusionist for the first time I was really taken by the scene where Ed Norton's character creates and gives the locket to his sweetheart. I quickly decided to design such a locket, but after seeing a variety of nice designs floating around on the web I pretty much gave up on it until having this idea to create a box based on the same concept - one that can change shapes and only opens when in the heart shaped position. I've been calling it the Secret Heart after listening to Feist's cover song.
I tried to keep all the components printable or easily accessible at average local stores, but there are a couple random components in this version - either 2 small magnets or a spring from a clicker Bic pen along with a BB (or any small sphere about .17" in diameter). The magnets are really the best to use because they keep the box in the heart shape and keep the lid halves together when opened, but the spring and BB seem to work decently if you can't find magnets of the right size. If you do use the magnets then the spring and BB only act to keep the box in the rectangular shape, which isn't a big deal since friction seems to do a good job of it. I've uploaded a few different variations of the lid for this design, each with a different hole size for different magnet sizes, so hopefully most people can find a usable magnet. If anyone has a request for a different magnet hole size let me know as it's pretty easy to change the model and make new STL's.
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Assembly instructions and BOM are included in the PDF drawing attached.
Print one each of all the included parts, 2 of the Hinge Covers. All my parts were printed in PLA with .15mm layer height. The Lids, Bases and Hinge Block were printed with 50% hex infill and the Pivot pieces with 100% infill. The default coordinate systems make all parts printable within a 100mm square build area and I used a skirt of 2 passes at zero offset for the lids and base. You may want to use a wider skirt with zero offset (called 'The Brim' as named by Idolcrasher, who discovered how much it helps reduce warpage) if you have a larger build area.
I used Kisslicer for all the parts except the bases, which I used Slic3r for because for some reason (that I couldn't figure out) Kisslicer was generating some strange paths that were causing problems for those parts. All the STL's have been run through Netfabb already fyi.
Without a heated bed you'll get some warping at the pointed tips and rounded ends of the base and lid pieces, but for me it ended up being pretty uniform across all those parts and so it's not really an issue in terms of the pieces looking off with respect to each other.
If the hinge covers crack a bit when installing the set screws they will still probably work fine - almost all the hinge covers I'm using have cracked at least a little bit and I don't really want to beef up the wall section around the set screws because it means larger cutouts in the back of the part. If the hinge covers completely break from the set screws you might want to use a size 7/64" or 1/8" drill bit to clear out the holes, but doing this means the hinge won't have (as much) friction and won't feel as nice.
The thin walls at the rear of the base pieces might be pretty fragile until you install the hinge covers, so be careful not to put too much force on them until the assembly is complete.
Cleaning up the edges of the lids and bases is pretty important for allowing the two halves to rotate nicely and without catching an edge, so be sure to sand or file the edges on those parts. You'll also probably need to clean up the edges at the bottom of the hinge covers a bit so that they fit into the base without applying much force. After having some issues with the rotation on some builds it's clear that the pivot hole should be nice and clean too.
I used JB Quick Weld epoxy to pot/adhere the magnets in my parts and it works really well, but it does stain the PLA pretty easily so be careful not to get it on visible surfaces if you use it.