Ikea has started making those little cams you use to assemble their Billy bookshelves out of plastic. So guess what happened when a friend was assembling theirs? One of them snapped, and Ikea didn't include any spares. 3D Printer to the rescue! (It's becoming a habit with Ikea parts now: http://www.youtube.com/watch?v=Yv98JTozZQQ)This is a tricky little part to print. Best tip: Print several at a time. Not only will you have spares when you snap more, but it'll also print better as each layer will have more time to cool. It's oriented to be printed on its side. This minimises the amount of support material needed, but you might need to include some support material or a brim (slic3r option) in order to keep the cam stuck to the print bed during printing. In the 3rd picture (group shot) the cam on the left of frame is one printed 'upright' and with support material to support the top of the cam. That took a while to cut out... Print Settings & Hints: If you have ABS, I'd recommend printing with that first, as it's more flexible than PLA. I printed this with a 0.2mm layer height, although finer is going to be better. 2 perimeters 3 top & bottom layers 40% infillUse: Once you've cleaned up your print, insert it into the cam hole in the bookshelf and turn it with the screwdriver until it engages. Don't turn it as hard as you did when you snapped the first one!This isn't a direct copy of the original cam, but is functionally the same. The cam is modified somewhat from the original in order to strengthen up some areas and adapt the model for 3D Printing, rather than the injection molding process used in the original part.