IKEA Billy Bookcase Joiner

I put four of IKEA's “Billy” bookshelves in a room and found them to stand slightly unevenly, probably due to the uneven floor. Like every problem I encounter nowadays, there was a way to 3D print a solution! This little bracket did the trick. Find four little screws and you're in business. I recommend printing this at 100% infill, but I did my example at 10% and it felt surprisingly strong even when screwed in place. I used PLA and have no concerns about warping since the room is almost always pretty cool. 

If you want a version of this that's longer than the 8cm or whatever I ended up making this, you can simply put two into your slicer and line them up perfectly end-to-end to produce one that's double the length.