# Spring Constant

• posted

Hello,

Cannot understand Carr Mc Master 'spring constants' in their spring section.

They state 'the spring constant is the number of pounds force required to compress the spring one inch'

The spring constants being given seem to be far too large. A long 36 inch spring being made out of 0.013 inch wire has a spring constant of 4.8. ie it takes 4.8 pounds to compress the spring one inch.

Where am I going wrong.

TIA.

Jack

• posted

Skipping, or sleeping through, high school physics?

Try googling "Hooke's Law" or "F = -kx".

• posted

wrote: (clip)it takes 4.8 pounds to compress the spring one inch. Where am I going wrong. ^^^^^^^^^^^^^^^^ I don't see anything wrong with a spring constant of about 5 lb/in on a spring like that. We're talking about a coil spring in compression or tension, right? You don't state the diameter of the coil, or the turn spacing, but it seems reasonable to me that if you compress a spring about

3% of its length, you might expect to exert about 5 lb.
• posted

You neglected to say that the spring is question has an OD of .094"

And this section of the catalog is for continous length which states:

Springs have open ends and can be cut to the length you need. Great for manufacturing, utility, and maintenance jobs. To determine the length (in inches) to which to cut your spring, take the spring constant and divide it by the number of coils per inch. Then take this value and divide it by your desired spring rate in lbs./inch.

From what I can tell, this means that the spring constant is NOT the K value from your textbook but the spring value for ONE turn. DIVIDE by the number of turns to get the spring constant from the textbook.

D> Hello,

• posted

Spring constants are dependent on the wire size, coil diameter, number of coils and material.

A coil spring is really a torsion spring formed in a spiral. When compressed or extended beyond it's rest length the wire is being twisted, not bending.

Smaller or fewer coils means that the wire is shorter and must be twisted more to compress the spring the same distance. Therefore it would have a higher spring constant.

Fred

• posted

Thanks for that, I am inclined to say that they are using the term "Spring Constant" in a not so very scientifically correct manner :-|

The spring is no good for me as it has too many turns per inch.

Cheers

• posted

Hey, thanks Fred! I never stopped to think about coil springs working that way, I just stopped at "Pull it and it stretches, pull it twice as hard and it stretches twice as far."

That hit me about the same way as the first time someone pointed out to me that the "working fluid" in my car's engine isn't gasoline, it's air. The gasoline just heats it and makes it expand.

Jeff

• posted

And to carry this a bit further, the wire in a typical torsion spring is primarily subject to bending, i.e., it's a coiled up beam.

Ned Simmons

• posted

"Ned Simmons" wrote: And to carry this a bit further, the wire in a typical torsion spring is primarily subject to bending, i.e., it's a coiled up beam. ^^^^^^^^^^^^^ Let's unscramble this a little. A "torsion spring" is an elastic bar subject to twisting--not bending. A "coil spring" is a torsion spring that has been wound into a helix for compactness. A "leaf spring" is a beam in bending.

• posted

A torsion *bar* is an elastic bar subject to twisting, a torsion

*spring* is a helical beam - like this...
Or a beam coupling...
Ned Simmons
• posted

Which means I suppose that a "clock spring" is just an extra long "leaf spring"?

Jeff

• posted

"Jeff Wisnia" wrote: Which means I suppose that a "clock spring" is just an extra long "leaf spring"? ^^^^^^^^^^^^^^^^^^^^^ A "clock spring" is a spring that drives a clock. It so happens that all clock springs ARE "leaf springs." (As far as I know.) ;-)

• posted

[Middle English torcion, wringing pain in the bowels, from Old French torsion, from Late Latin torsi?, torsi?n-, a wringing pain, variant of Latin torti?, from tortus, past particple of torqu?re, to twist. See torsade .]

?tname=torsion&curtab=2222_1&hl=torsion&hl=bar&sbid=lc03b A matter of semantics [The meaning or the interpretation of a word, sentence, or other language form: We're basically agreed; let's not quibble over semantics.]

A* torsion bar* is a *spring*

Fred

• posted

I wasn't quibbling over semantics I was nitpicking about technical jargon .

Agreed, but a torsion bar is not what's typically meant by the term "torsion spring".

Ned Simmons

• posted

That's why we *drive* on a *parkway* and *park* on a *driveway*.

• posted

"ff" wrote: That's why we *drive* on a *parkway* and *park* on a

*driveway*. ^^^^^^^^^^^^^^^^^^ And send shipments by car, and cargo by ship.

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