Why is it a "bottom bracket" and not a "crankshaft"?

[SkipdiverJohn]

The term most likely dates back to the invention of the modern bicycle as we know it - the "safety" with the familiar frame and transmission layout. Before that time, other configurations of frames and drives existed, and still do today in tiny numbers.

 

[classic33]

More likely the name was carried over from larger machinery, as it did the same job. Reciprocating motion being converted to circular motion.

 

[mickle]

Another description is chainset bearings

Oh no it isn't.

 

[mickle]

The bottom bracket is the frame part which retains the bottom bracket axle and it's bearings. This mouthful was abbreviated to 'bottom bracket bearing' and then just 'bottom bracket'. The frame part now referred to as 'bottom bracket shell'. This is my wild guess and I'm sticking to it.

 

[overmind]

I always get confused by the terms: seat stay and chain stay.

Here's a funny picture covering most of it.