Things you will need:
1/8" stereo jack (junker or a cheapo will do)
hot glue gun
dremel tool or drill
array of small drill bits
sandpaper / whetstone
3d printer (mine is an original Ultimaker)
PLA or ABS (I used glow in the dark PLA)
The construction and the assembly is quite straightforward. I'll try to describe the process as clearly and simply as I can, but it was seriously very easy. If you managed to build your printer, you can build this for sure.
First take apart the headphones (I'll try to include pictures of this later).
You'll notice that the battery and a speaker on the right side and the circuit board and a speaker are on the left side. You'll want to desolder the battery, speakers, and all the wires from the circuit board.
The circuit board has very clear labels on each solder point, so I'll leave it to you to figure out which one is for what for now.
Now we have a battery and a circuit board. The contacts for the battery are on the "top" of the circuit board, along with a couple of speaker contacts. The other speaker's contacts are on the bottom.
I used the wire that came in the plastic band to rewire my speaker contacts to the stereo jack. This kind of wire is pretty easy to solder, but you need to prepare the end by burning or scraping off the insulating film. I find that burning it off with a lighter is the simplest way to go about it. Just be ready to blow it out because it burns like a fuse once it ignites. If you hesitate you'll end up with a bare wire with no insulation anywhere.
I also went ahead and soldered both speaker grounds to the one ground on the stereo jack, just to be safe and certain. Common sense would indicate that the ground would be the same, but I can't be sure and its easier to solder a quick extra wire than to run into problems later.
So now wire up your speaker contacts to your 1/8" stereo jack. Google the pinout to see which channel goes where and which point is for ground.
Now that we have the speakers wired up, cover those contacts with a bit of tape so that we don't accidentally touch them with the soldering iron or the wires coming from the battery. Make sure to tape up the end of the battery that you are not currently soldering or it will probably bounce around and start ruining electronics left and right. If I remember correctly, the positive wire should be soldered first. Be sure to cover that with tape too once it is connected before finally soldering the negative side. (Technically it shouldn't matter but people think its safer in this order. Feel free to disagree in the comments.)
Now we have an operating bluetooth stereo headphone device, and it's time to prep the case for installation.
If your printer is like mine vertically printed circles are a little ugly. Smooth those babies out with your drill bits. Personally I like to do it by hand and at first give a little twist to get it in, then pull it straight out. This makes a nice uniform circle. If you need to increase the size of the hole, just start small and work your way up.
I'm not exactly sure why I originally made the buttons different sizes, but in the end it helps identify them by touch. If you want, you can use the scads to resize the holes and buttons. I recommend printing out everything all at once and then match up the best fitting peices. As long as your headphones are the same as mine, everything will line up perfectly.
The microphone hole needs to be drilled. I thought about putting it into the design, but since it is so small and my vertical holes a little ugly, I thought a fresh drill would be best. Be careful when placing the hole, the wires on the mic don't stretch very far. Make it as close to the microphone as possible.
The microphone and the stereo jack can be secured in place with a little bit of hot glue. It adheres wonderfully to PLA and is easily removed if you want to change anything at a later time.
You might notice that the longer buttons have guiding supports. In my original design, they weren't present. One button needed them and the other didn't. I added them to the one and then when I reprinted, the other one ended up needing them too. I have added them to both buttons. My photos only show the one. I'm going to just add them with hot glue so I don't have to print out everything and clean up the holes all over again. They should be ok for you. Again, if you run into issues the scads are all included.
(Let me take this moment to apologize for my ugly scads. I make things for myself and when I am particularly proud of something I share it. I can't be bothered to go back and comment everything, but if you're changing scads you can probably read them ok. I also don't make them very elegant. I mostly union and difference primitives into what I need. Trig functions and whatnot are not really my cup of tea at the moment. Sorry!!)
The buttons are all properly sized, but are small and a little hard to print. I found that 10 mm/s print speed @ 200C is perfect (glow in the dark blue PLA). I also manually blew on them to help them cool a little faster and remain cleaner. The longer ones will need a little sanding to get them to move smoothly. If they are too tight they will depress, but never come back up. Looser is better, but too loose and they might fall out or not line up properly. They only take 1 min to print, so if you mess up, just try again. Again, scads are included, and they're VERY simple objects, so easy to edit.
When attaching the circuit board to the case, I used 2 of the screws that came inside the headphones. Then I simply used my soldering iron to slowly push them into the raised studs. Once it cooled, I gave a short little turn with the screwdriver to make sure they were tight. Closing the box is done in a similar way.
First make sure you have the battery sitting in a spot that keeps it below the top of the box or it will probably push against the power and play buttons on the bottom. Simply put the top on and line it up nicely. The slightly sunken areas are where you can use screws or (as I prefer) simply slide the tip of your soldering iron in a little ways and weld it shut.
I think that's about it. Since taking the pictures, I have attached a keyring and carabiner to the lanyard loop, which is what that round thing on the outside was designed for. I can quickly and easily clip it to my backpack or belt loop and not have to worry about losing it or fishing for it whenever I want to change a song or turn up the volume.
If you have any questions or comments, please feel free to ask!