Adjustable spring rate compression spring?

[hawaiilover]

I need to know how to set compression of one coil spring to 20 lbs.,40lbs. and 60 lbs. The spring will be housed in a cylinder and needs to easily be adjusted manually. Any suggestions? I'm stumped. Thanks alot.

 

[sbozy25]

I am not sure if I am reading your question correctly. Are you asking how to know when you have the spring compressed to those forces? If that is the case, this is an easy solution.

If you know the spring rate, just compress the spring the distance needed to obtain that force.

For your cylinder, you could perhaps drill holes in the side at the given deflections. Then as you push the spring past that point, slip a pin in to stop the spring from returning.

 

[sreid]

If you need to change spring rate, you could keep some of the coils inactive. By, say, putting a pin through the coils at half the spring length you would double the spring rate.

 

[sbozy25]

Bad Idea... do not insert a forgeign object between coils of a compression spring. that will cause premature failure 100% of the time. If you want inactive coils, have the manufacturer coil them dead.

Or if you were looking for somethign that had an increasing rate... Try a variable rate spring. There are tons of ways to do this, ie. varry the wire size, varry the pitch, varry the diameter...