Another spring question

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

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.

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

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.

Reply to
Ecnerwal

Wow. I thought my view cameras were heavy :-).

At 6", if it's still linear, then you're pulling on it with 72 pounds.

If it's a "stock spring" then the manufacturer probably makes a recommendation about maximum extension. You can usually go a little more than that, but going from a 3.5" max to 6" will probably deform it.

Actual max extension depends on many parameters including material, dimensions, preload, and heat treatment.

Good tutorial on the web that I HIGHLY recommend:

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Tim.

Reply to
Tim Shoppa

If it is an compression spring (at least designed for), you can compress it until it is a block. That travel is OK for the reverse direction too.

HTH, Nick

Reply to
Nick Müller

Get one and try it. Most likely, it will take this overtravel, but that will shorten its life somewhat. The 6" extension will be about the limit, I'd guess. Once you exceed the absolute elastic limit, the spring will no longer contract fully, so you will know that you've found the limit.

Jon

Reply to
Jon Elson

The rated load is usually set to keep the material below its fatigue limit, i.e., if the spring must go thru many load/unload cycles without failing, you should stay below the rated load. If you can find a number for the fatigue limit for the spring material and compare to its yield, you'd be able to make a SWAG on the load that would permanently stretch the spring.

Or try one of the spring calcualtors here and analyze the spring or design your own...

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Ned Simmons

Reply to
Ned Simmons

But many compression springs will fail prematurely if used this way in a cyclical application.

Ned Simmons

Reply to
Ned Simmons

Buy two of 'em and connect them together lengthwise?

GWE

Reply to
Grant Erwin

Yes. You can calculate the material stress on a given spring using formulas, and predict the cycle lifetime from that stress. I do it for torsion springs on my Web page at

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and Machinery's Handbook has data for other types of springs.

Reply to
Richard J Kinch

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