This guy made the Difference Engine with Meccano parts. The most interesting part to me is how he was forced to adapt the gears to store the decimal numbers Babbage’s designs require:
“Meccano does not provide us with too many examples of tenfold symmetry, so representing decimal numbers is a challenge. Fortunately we can depend on the following two observations. First, by meshing a 95t gear wheel with a 57t gear wheel we get a ratio of 5:3. This means that 1/10th of a rotation of the larger gear corresponds to 1/6th of a rotation of the smaller one, and we have available the 6 hole bush wheel. This can provide a detent mechanism to hold the smaller gear in one of 6 positions, corresponding to holding the larger one in one of 10 positions. Second, we note that the ratchet wheel has 20 teeth. Had not this been a multiple of 10, construction of the mechanism may well have been much more difficult.”
Web link of note: Meccano Difference Engine
(At http://www.meccano.us/difference_engines/rde_1/index.html)