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Coil Gauge Question, Please 13 Apr 2021 15:44 #1

Hi, all.
I know there are a lot of factors affecting how soft/firm a mattress feels, but specifically about coils:

-1- Can someone explain the effect that coil height has on softness/firmness for a given gauge? For example, is it correct that 15ga in a 4" coil would feel softer than 15ga in an 8" coil?
-2- What about number of coils? If you have 1000 coils at 15ga, would that feel firmer or softer than 750 coils at 15ga?

Thank you.

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Coil Gauge Question, Please 13 Apr 2021 16:55 #2

With respect to question 1, the spring constant expresses the force per unit length of deflection, i.e pounds force per inch of deflection.

The basic equation for a spring with round wire is k = G*d^4/(8*n*D^3). As you can see, if all else is held constant, then as n (the number of turns) increases k (the spring rate) decreases, where n is the number of active coils (the turns that can actively compress). So the spring rate, with all other things being equal is a function of the number of turns, rather than the spring height.

www.mitcalc.com/doc/springs/help/en/springs.htm#Header_2

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Coil Gauge Question, Please 13 Apr 2021 17:06 #3

-2- What about number of coils? If you have 1000 coils at 15ga, would that feel firmer or softer than 750 coils at 15ga?
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It would be firmer if all else is equal (i.e. G, d, n, & D) . The same load would be distributed among more springs, so each spring carries less load, and the deflection for each spring would be lower.

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