Merde!

D = 6" not 13"


I hate it when my tape measure lies to me. I'm glad you got it figured out.
Simple coil springs are one of those very basic yet very interesting devices
that have endless applications.

Also, it brings home the principles of the formulae to me. One good
thing

Having an understanding of the principles of their design makes it a lot easier
to select and use them whenever and wherever you need them. The equation used
for compression springs can be applied to tension springs as well but you have
to watch out for preload resulting from the coils being closely wound. The
actual value of k doesn't change but the amount of force required to stretch
the spring the first small distance to separate the coils can vary widely.
Ahh, springs! Valve closers, catapults, pogo sticks.......



Richard Coke