If I make a helical spring out of size X music wire, of length L and
diameter D, with N number of turns, does anyone have a formula for the
spring constant? This could be in pounds per inch or any other units you
care to give. I don't need rocket science accuracy.

Thanks,

Will

Will Self wrote: (clip) does anyone have a formula for the spring constant
(clip)
^^^^^^^^^^^^
I don't have a formula, and I don't even know where to look for it, but, if
no one else provides one, I can suggest a way of deriving it. A coil spring
is just a torsional spring wound into a helix, to make it more compact. So,
if you think of your wire as a torsional spring, you can calculate how many
degrees of rotation it will take to close it a certain amount. Then apply
the formula for torque vs angular rotation (which I haven't looked up
either.)

I would buy them if I could. I have pored over the MSC catalog looking for
what I need. Of course, I can make some and then measure them, and in fact
will probably do that, but a formula to guide at the outset will be a great
help. I'm eager to try out Dave Baker's formula. Thanks, Dave!


"tony" wrote in message
...
are you trying to figure out the spring constant
of springs you already have? or are you trying
to make springs of a particular strength?

former: measure it
latter: buy them

unless its a twisted brain-puzzle in which case,
have fun!

I bookmarked this site years ago years ago and have found it useful on
several occasions http://home.earthlink.net/~bazillion/intro.html

Best I have found on the web for spring winding.

If you have a good collection of Home Shop Machinest the May/June and
July/August '87 issues have all the tables and graphs.

Will Self wrote:
If I make a helical spring out of size X music wire, of length L and
diameter D, with N number of turns, does anyone have a formula for the
spring constant? This could be in pounds per inch or any other units you
care to give. I don't need rocket science accuracy.

Thanks,

Will




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Sun, 3 Aug 2003 14:01:59 -0600, "Will Self"
wrote:

If I make a helical spring out of size X music wire, of length L and
diameter D, with N number of turns, does anyone have a formula for the
spring constant? This could be in pounds per inch or any other units you
care to give. I don't need rocket science accuracy.


Will this one work? I don't really understand spring rate
calculations this but google turned this up on public side of efunda:

http://www.efunda.com/designstandard...%2 0constants

Here it is in the short form: http://tinyurl.com/ixgm


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The standard equation for a helically wound spring with round cross section is
:

k (expressed in pounds per inch) =(d^4 * G)/(8*N*D^3)

where d= wire diameter(inches), D = mean diameter of the coil(inches), N =
the number of free turns,
and G = the modulus of rigidity(aka shear modulus) For steels this value is
in the range 11e6 to 12e6 so using 11.5e6 lb/in^2 will get you close.

Richard Coke

I found those articles in HSM to be very good. Since the data is presented
in the form of nomographs, it is very easy to zero in on your specific
spring needs. I have made about 30 springs using them and have been
impressed with their accuracy. There is also a formula and chart for sizing
the mandrels for lathe winding a given diameter spring which is very good .

Randy


"Glenn Ashmore" wrote in message
...
I bookmarked this site years ago years ago and have found it useful on
several occasions http://home.earthlink.net/~bazillion/intro.html

Best I have found on the web for spring winding.

If you have a good collection of Home Shop Machinest the May/June and
July/August '87 issues have all the tables and graphs.

Will Self wrote:
If I make a helical spring out of size X music wire, of length L and
diameter D, with N number of turns, does anyone have a formula for the
spring constant? This could be in pounds per inch or any other units
you
care to give. I don't need rocket science accuracy.

Thanks,

Will




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Will Self wrote:

I would buy them if I could. I have pored over the MSC catalog looking for
what I need.

http://www.centuryspring.com/catalog.html
These guys have an excellent search engine of their stock which is the
largest inventory I've ever seen. Post back with part numbers and
quantities if you need prices.

On 03 Aug 2003 20:40:01 GMT, a (Dave Baker) wrote
something
.......and in reply I say!:


PMFJI.

Can you parethn....pra... you know, put brackets in your formula? G
I tried applying it various ways and got crazy answers.

And do you mean dims in mm, but answer in lb/inch?

Thanks in advance.

With dimensions in mm.

Spring diameter (D) = mean diameter i.e. o/d minus wire thickness (or i/d plus
wire thickness of course)

Number of working coils (N) = fully compressed length divided by wire diameter
minus a further 1.7 (to allow for dead coils at each end)

(d) = Wire diameter

Spring rate in pounds/inch is

d^4 / D^3 / N * 60,000


************************************************** ****************************************
I could never _see_ myself as anything!

Nick White --- HEAD:Hertz Music
Please remove ns from my header address to reply via email
!!
")
_/ )
( )
_//- \__/

Subject: Formula for spring constant?
From: (Old Nick)
Date: 12/08/03 11:36 GMT Daylight Time
Message-id: 3f38c1b4.18433483@localhost

On 03 Aug 2003 20:40:01 GMT, a (Dave Baker) wrote
something
......and in reply I say!:


PMFJI.

Can you parethn....pra... you know, put brackets in your formula? G
I tried applying it various ways and got crazy answers.

And do you mean dims in mm, but answer in lb/inch?

Thanks in advance.

With dimensions in mm.

Spring diameter (D) = mean diameter i.e. o/d minus wire thickness (or i/d
plus
wire thickness of course)

Number of working coils (N) = fully compressed length divided by wire
diameter
minus a further 1.7 (to allow for dead coils at each end)

(d) = Wire diameter

Spring rate in pounds/inch is

d^4 / D^3 / N * 60,000

I can't honestly see what could need parenthesising but anyway

Let spring be as follows:

o/d 34mm
wire diameter 4mm
compressed length 28mm

d = 4mm
D = 34-4 = 30mm
N = (28/4) minus 1.7 = 5.3

rate = 4^4 / 30^3 / 5.3 * 60000 --
rate = 256 / 27000 / 5.3 * 60000
=107 lbs/inch


Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
I'm not at all sure why women like men. We're argumentative, childish,
unsociable and extremely unappealing naked. I'm quite grateful they do though.

On 12 Aug 2003 13:07:13 GMT, a (Dave Baker) wrote
something
.......and in reply I say!:

Thanks for the clarification. Your formula agrees with Richard Coke's,
and my spring has a smaller D (6" not 13"). So my spring now rates at
950 lb/inch. Now _that's_ a spring! G

Sorry about all that.

************************************************** ****************************************
I could never _see_ myself as anything!

Nick White --- HEAD:Hertz Music
Please remove ns from my header address to reply via email
!!
")
_/ )
( )
_//- \__/

Merde!

D = 6" not 13"


I hate it when my tape measure lies to me. I'm glad you got it figured out.
Simple coil springs are one of those very basic yet very interesting devices
that have endless applications.

Also, it brings home the principles of the formulae to me. One good
thing

Having an understanding of the principles of their design makes it a lot easier
to select and use them whenever and wherever you need them. The equation used
for compression springs can be applied to tension springs as well but you have
to watch out for preload resulting from the coils being closely wound. The
actual value of k doesn't change but the amount of force required to stretch
the spring the first small distance to separate the coils can vary widely.
Ahh, springs! Valve closers, catapults, pogo sticks.......



Richard Coke

On 13 Aug 2003 14:25:05 GMT, (Richard Coke) wrote
something
.......and in reply I say!:

Well, thanks for talking it through. And interestingly, I was just
wondering about tension springs. I will have to do some looking up.

Merde!

D = 6" not 13"


I hate it when my tape measure lies to me.

Measure twice post once G

I'm glad you got it figured out.
Simple coil springs are one of those very basic yet very interesting devices
that have endless applications.

Also, it brings home the principles of the formulae to me. One good
thing

Having an understanding of the principles of their design makes it a lot easier
to select and use them whenever and wherever you need them. The equation used
for compression springs can be applied to tension springs as well but you have
to watch out for preload resulting from the coils being closely wound. The
actual value of k doesn't change but the amount of force required to stretch
the spring the first small distance to separate the coils can vary widely.
Ahh, springs! Valve closers, catapults, pogo sticks.......



Richard Coke


************************************************** ****************************************
I could never _see_ myself as anything!

Nick White --- HEAD:Hertz Music
Please remove ns from my header address to reply via email
!!
")
_/ )
( )
_//- \__/