A friend asked if I could help him with a Christmas gift for a friend by making some kind of bank on my MakerBot. Well I really liked Sublime's Skull Bowl, and it seemed like the perfect thing to make a cool looking bank out of. My friend said it would be OK if the bank didn't open, but what fun would that be?
So I used the Skull Bowl model, and used Syvwlch's great screw library to put a screw in plug in the base of the model to get coins out of, with a little tab on it to make it possible to turn. Intersecting the screw with the skull took OpenSCAD some time, but it looks great when closed. The slot for putting coins in is in the back of the skull on the top piece.
The zip file contains everything you need to mod. The Skull has been resized a few times, so the dimensions don't match the original. Since I'm not sure what the scale factor is (from memory, 60%?), I've included my copies. They probably aren't the latest version, since I see it's been updated. The three OpenSCAD files are in there for making adjustments.
Included in the pictures to the side are a cut down version of the screw section so that I could test it without having to print the entire skull, and the first version of the lid where I put the wrong slot length in so quarter's wouldn't fit.
Warning: I couldn't get the lid to fit flush. When I view it in OpenSCAD it's fine, but no matter how many times I flipped the lid along the Y axis the first layer always seemed to print in the same direction. I have four copies of the lid. I hope you have better luck than I did.