Secret Heart box

by EricYoung, published

Secret Heart box by EricYoung Jan 1, 2013

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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.


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.


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I really like the design for this. Im going to print this on my UltiMaker2 as soon as i am home from work.
I have 1 question tho. Where did you order the magnets? And do they have to be in there??

I've been looking for this locket since I watched the movie 5 years ago.
Loved your design. Now I just need to buy/make a 3D printer. I'm on my way...

Thanks :)

You can buy the locket online if you want, they cost around $200. Google "illusionist locket" and it'll be the first link. There were also one or two less expensive versions on Ebay last I checked.

Great documentation!

Thanks, I felt like it might have been too much info so glad if it helped you.

Hi Eric, I printed from the zip the two base parts and both came as female in the middle, totally different from the pdf and pictures. Am I missing somthing other than the Pivot Main and Pivot Nut Cap to join the base parts? Here are pics: http://imgur.com/a/1qlDUhttp://imgur.com/a/1qlDU

Hi Soke, it looks good to me. Those female grooves are for the lid catches (to keep lids closed until unlocked), so they are supposed to look like that.

One thing I forgot to mention about that thin walled version is that you need either a #4-40 x 3/8" long or M3 x 9mm long flat head machine screw for the pivot rather than the one called out in the drawing, since the walls got thinner. Good luck!

Eric this piece is wonderful! It was really a challenge for my printrbot+. A lot of cleaning up had to be done for the hinges to work properly and for the lids to align with the rest of the design, mine isn't nearly as flush and good looking as yours but I am very happy I was able to put it together, Thanks for the great design and amazing documentation. http://imgur.com/a/cf50Rhttp://imgur.com/a/cf50R

Thanks Soke, it's really gratifying to see people post their prints. Glad it worked out in the end.

Printing as I type.

Last piece....Just waiting on magnets!

Thanks for this great piece!

You do magnificent work, Eric!
Love your layout too!

Love this part :) If you fancy winning a $2,500 printer of your choice or material visit http://www.big-3dp-survey.comwww.big-3dp-survey.com

Hi, Im trying to source the hardware to make one but im not sure what you mean by #4-40 set screw, hex nut then #4-40 x .50" for the socket flat head cap screw.

Do you mean M4? What are the required lengts of the screw and set screw?


Yeah the #4 screws are in Imperial Units as I'm in the USA. You can use M3's in place of #4, they're basically the same dimensions.

For the set screws I think anywhere between 6 and 10mm length should work. The pivto screw should be a 12mm long machine screw and hex nut. The wood screws should also be about 12mm long, though 10mm should work too.

Very nice job and thanks for sharing. I'll have a go at a print tomorrow.

That means a lot coming from you , thanks :)

So awesome. Just ordered the missing pieces and will start the print tomorrow for V-Day this year

Sweet! Let me know if you run into any issues or have any suggestions for changes etc.

So far no issues with the print. I recommend a no offset brim as you did to avoid curling at edges of lids. Biggest problem is the darn line that appears on the lids from the infintessimal bump the join in my painters tape makes. Why don't they make that stuff in 10 inch strips :)

If you are printing with PLA and a heated bed, just turn on bed to 60C and PLA at 200-205 then print directly on the glass. Just give it a wipe before printing to clean off any oil or dust. Then once your print is finished, let the bed cool down, and the part will literally pop right off no spatula needed and the base of print , well you guessed it SMOOTH as glass(: Once you do this you will begin to love your machine because guess what, NO MORE TAPE:D You will be smiling watching the first print, and you will giggle with excitement when the bed cools and not before, have to wait then it will pop right off. be careful with small parts, once they break free just slide it off the edge because they are stuck by vacuum force. Hope this helps and changes your whole printing experience, because I know it did mine(:

Good to hear and thank you for your input.

One issue I've run into since posting this design is that the rotation of the two halves for some builds is really 'catchy' for lack of a better term. This causes the pivot screw to loosen eventually, which sucks. I haven't had the time to figure out the definite cause, but think it's probably that either the Pivot pieces are too bumpy or the holes in the Bases are too bumpy. So those areas might need some extra attention fyi

Don't even get me started on those friggin tape lines :) It shouldn't be hard for 3M to slit their painters tape to various widths during the conversion process. Maybe if enough people are using the tape someone could organize a crowd-funded custom order on the Reprap forums. Hmmm.

Re: the war on lines across prints. I am having very good luck with green Frog Tape. 1 layer of painters + a layer of that. You can get very very crisp joins with it and it reduces the line factor a LOT. Additionally it doesnt flake off like painters tape and leave a blue residue.

Good to know, thanks!

I just received my Makerbot 2 and it came with 3 strips of painters tape that are about 12" by 7", so it definitely exists. Wish I could help more by giving you a brand name but unfortunately there isn't one.

As for your design, I am really looking forward to trying it out after I hunt down some magnets for the appropriate size. In the meantime, I'm 10% in to printing your iPhone dock - it looks great so far!

Cool, thanks for the info and good luck with the prints :)

Very nice, thank you very much for your hard work.

Thank you, that's really nice to hear as this one took a whole lot longer than I'd hoped to figure out a mechanism that both worked well and was 3D-printable. I'm still getting used to taking advantage of the capabilities of 3D printers to make certain features and ended up going through over 1kg of filament on prototypes. Gave one of the prototypes to my cousin for Christmas though and just seeing her reaction made it all worth it.

Excellent! My 2012 V-Day printed present for my wife was the Heart Gear. I was still new to my ToM and didn't get it finished in time. This will be my 2013 V-day printed present, with plenty of time (and lots more experience) to get it done right!

Great! I hope she likes it :)

I'm interested to know how easy this is for others to print and assemble, so if you run into any problems or have any suggestions for improvements let me know.