Tipping Egg / Sand Timer / Hourglass

This egg timer falls over when time is up and can also be re-set at any time. This is only a 30 second proof of concept model, but longer times would be possible if the design was tweaked to allow more sand and/or a smaller sand hole. The timer was originally designed to solve a problem with the egg timer in the board game Pictionary.  See a video about the project below:

The model can be printed without any support material flat on the bed. The transparent front is thin acetate (100 micron) that is glued on using a glue like Uhu. I normally use an over-sized piece of acetate and then trim it a back when the glue has dried (I've also include a .dxf and .svg of the front acetate shape in case anyone wants to laser cut this). 

The sand has to be very fine - I used this craft sand. It's crucial that the sand is completely dry before putting in the timer or it will clog the hole and stop working. I normally dry it out on a radiator before putting it in the sand timer. In terms of how much sand you need, it's just enough to fill the bottom chamber, although as this is proof of concept I haven't dived into precise measurements as yet. Once I roughly measure out the amount of sand I need, I then stick the front on so it's sealed in.