Crank pin idea

Beautiful summer weather rarely inspires much railway modelling. It’s a better time to sit on the deck and enjoy the outside of the house than the inside of the basement. Today the idea book came with me so I could capture that elegant crankpin solution I suggested a month or so ago.

I believe that screws have held drive rods onto model locomotives pretty much ever since the wheel was invented. As it’s impossible to get at the back of the drivers once they’re in the frame, the head of this screw or a nut must be at the end of the crankpin. On North American locomotive, the real rods are often held in place by a split bearing held in place with a wedge (probably the Germans have a superior mechanism and the French have an highly-complex one that requires a PhD to operate). Not only is the nut unsightly, but for some engines there’s no room for it!

Someone mentioned that M0.3 screws might be available, which set me to wondering whether they could be used to hold rods on more prototypically. In the end, I concluded they’re not necessary, and a blob of white glue would be sufficient to keep my solution in place, while being easy to remove when necessary.

The idea is this: create a slot in the middle of the rod end, into which a tiny “n”-shaped key slides from above. The key engages with a slot in the crankpin to keep the rod from sliding off the end of the pin. The critical dimensions of the rod and the bearing surface of the crankpin would remain the same: the key would only be for retention.

Not only does this design yield a better appearance but also a potentially stronger crank pin. It could even be steel, to help with wear against the nickel silver side rods.

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