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compression spring force and active coils

compression spring force and active coils

compression spring force and active coils

(OP)
If you have two compression springs and everything is the same except number of active coils, which will take more force to compress? The one with more coils or one with less coils?

Take for example:
Spring 1= 6 inch long, 1in outer diameter, 0.1" wire diameter, 10 active coils - compress 2 inches
Spring 2= 6 inch long, 1in outer diameter, 0.1" wire diameter, 8 active coils - compress 2 inches

Everthing I find (spring creator tools, equations, etc) says that spring 2 would take more force to compress, although I am not understanding why and feel spring 1 with more coils should take more force to compress? What logic / theory am I not understanding?

https://www.engineersedge.com/spring_comp_calc_k.h... (equation - k = gd^4/(8nD^3) where n= number of active coils

https://www.thespringstore.com/ (spring creator tool)

RE: compression spring force and active coils

If you compress these from 6" free length to say 4".
In spring #1 each turn is being loaded with 0.2" of compression.
In spring #2 each turn will be loaded with 0.25" of compression.
So the coils will be resisting more deflection in spring #2 giving a higher force.
And remember in a coil spring all of the defection is seen as torsion in the wire.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: compression spring force and active coils

(OP)
Makes perfect sense! Thank you Ed. Knew there was some fundamental thing I was missing..

RE: compression spring force and active coils

Imagine the springs uncoiled and the same angle twist applied to each. The torque to twist the longer wire will be less than that to twist the shorter wire.

Ted

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