end of axle, divergent
軹 centers on the end of an axle, a specific mechanical part. The meaning "divergent" likely extends from the idea of something branching off or ending at a point.
軹 combines 車 (vehicle) with 只, which likely contributes a phonetic element. The exact historical development is uncertain, but the character is associated with axle parts.
The left side 車 is a vehicle, and the right side 只 looks like a stopper or cap. Picture the end of an axle where the wheel is secured, like a cap that keeps it from diverging.
For シ, imagine the axle end shearing off: shear -> シ, and the axle diverges from the vehicle.