Why were cottered cranks invented?

Question

I don't understand why people would have designed them like that when the cotterless design is much simpler.

Answer 1

Only guessing but I would think that in earlier times  - cottered cranks are simpler to produce - as milling a square end on a shaft requires a more complicated & expensive machines.

early bikes were turned out in back shed workshops

Answer 2

it was just the progression of design

Answer 3

In one way, it's simpler.  In another, it's not.

Look at it this way.  Take a one piece crank and break it into axle and crank arms.  You have to attach the arms to the axle.  So, what do you do?  Make a hole in the crank arm and figure out how to keep it there.  Cotter pins and keys existed; it was then an adaptation of current technology.  It also mitigated the need of drilling the inside of the axle and threading it.  And it is possible that the quality of steel available may have been prone to cracks when drilled in such a manner.

And if you look at some current FSA cranks, with a bolt holding the left crank arm onto the axle shaft, we're basically back to the same solution, just with a different way of locking the crank arm onto the axle.

Answer 4

That was the way it was,back in the day,when steel was cheap and alloy hadn't taken off.

Cotterless is better,and lighter,even though you usually need a puller to get the crank off.

Answer 5

Why were they invented?! That's the way they started.

The cotter was how machine tools used to connect gears and pulleys to machinery. Eventually this progressed to keys and set screws. So, I guess you could say the technology was borrowed from the machine trade.

Wait until you find a vintage bike with round shaft and keys.. they are out there, especially in the UK. Then you can also be priviledged (sic) to experience BSA (not BSC), Swiss, and Whitworth threads.