In article EqbZf.88820$YX1.64885@dukeread06,
"Glenn Ashmore" wrote:

Is there any rule of thumb about how far can stretch a spring before it is
"sprung". i.e. permanently deformed?

IME, no. Different springs, tempered differently, behave differently.
Consider a slinky as one extreme case, and a truck coil spring as
another.

I have found almost the perfect spring for my camera stabilizer project but
it is only 4" long and rated for 42 lb at 3.5" and I need it to extend a bit
more than 6". I am worried that if it bottoms out once it will never come
back to its original initial tension.

Basic farmyard engineering. Try it. If you were building 100's or 1000's
it would be worth figuring it all out either theoretically and/or on a
prototype. Since you are building just one, build it, try it out, and if
the spring fails, try a different one - small ones are not so expensive.
You can either try it on the project, or simply yank it out to the
length you think it needs to go to and see if it snaps back.

--
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