I wanted a sturdy keyring than could hold securely small things, electronical components, screws, nuts,screwer bits, liitle tools, etc. (Don't put inside candies or pills unless you print it in P.E.T. plastic!!) I don't ever know what kind of stuff I will need, so I thought about it and this is the result. A cute ellipsoidal ('Beaned') keychain hard to open (pressure is configurable as you tighten the spring). You just need a M3x30 screw, a small spring, a M3 nyloc nut (recommended) and some glue. Insert the nyloc nut in the top part, Insert the M3 screw into the spring and screw it into the nut from the bottom part. Depending of the spring size you may have to use a shorter M3 screw or cut it down. Do your proof till you feel the thingie can be opened/closed comfortably, then use some glue to fix the parts supplied to hide the holes and you are done!! The bottom hole filling part should be trimmed according to your setup. Easy and proffesional. Don't let your friends see it or you'll have to make some for them. You can figure out why I called it 'BeanBox'. Its not big but also no tiny. Its just the size I needed, it can hold 25 cm3. and works perfect for me. You have to file it a bit to get a perfect fit. Also nice results are got when sanding its surface. As you wear this thing in your pockets or necklace I don't recommend to paint it unless after painting you apply several varnish layers. Not a toy, it is designed sturdy to last. Remember at print time that the top part requires support !!
Hint: If you scale it up by a factor of 1.34. Then you have a larger version and you can use M4 screw/nut and a larger spring. Anyway the one showed in the pics is the normal M3 version. If you want a bigger one, you can try using a 1.67 scale factor and M5 screw/nut. If this is still not enough for you... then I challenge you to build the beast, scale it to 2.67 and use M8 screw/nuts (this should be insane insane insane hahaha, maybe you could even carry inside your lunch!!) As FreeCAD sources are included you can customize it to your will. Place a 'remix' with pics if you have a nice idea, I'll be happy to see it.
Hint: I printed mine in phosphorescent ABS to find it easily turning off lights, and also to a better "after print" processing. I am thinking about printing it on Ninjaflex but after print work would be crazy...
Hint: If you want it waterproof, just print it with any flexible filament.
Happy BeanBoxing !!!
UPDATE (08-NOV-2015): Added a top part modified to use the beanbox as a necklace in a more convenient way. Added a Open Hardware logo bottom version.
UPDATE (09-NOV-2015): Increased the size of the top into bottom inserting zone to allow a better seal for the waterproof flexible filament print. Unfortunately this forces a bit more sanding in non-flex versions. Anyhow a bit of sanding is required for a perfect fit in those versions. For the waterproof one just use stainless steel screw and spring.