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Discussion Starter #1
Hola amigos, spring rates sure is a popular topic, but apparently most people are confused about what is a "spring rate", so I wanted to make a few comments based on articles posted long ago by my friend John Bercovitz. In usual engineering terms it means the "spring constant" (force vs compression rate), but in "1911 world" a 16 lbs. spring is one that exerts 16 lbs. when fully compressed in the gun at the end of the slide 1.6" rearward travel.
Constant rate springs are linear devices: the force a spring responds with is directly proportional to the amount (distance) it is compressed from its free length. The distance and force are related by the spring constant which is a property of a given spring.
Since recoil spring manufacturers don't supply conventional spring data, it is useful to know how to calculate a spring constant. The obvious way is to put a weight on the spring and measure the spring's deflection, and there are kits to do this (or you can make your own).
Theoretically the formula for light weight springs (thin wire compared to outside diameter) is k = (G*d^4)/(64 R^3*n). G is the modulus of rigidity; its value is around 11.6*10^6 pounds per square inch for steel spring wire. It is different for other materials, such as stainless steel. d is the diameter of the spring wire. R is the radius from the axis of the spring to the center of the spring wire; numerically, that would be half the quantity (outside diameter of the spring minus the diameter of the spring wire). n is the number of active coils (...don't count coils which are touching each other at the end of the spring).
In the case of any coil recoil spring of the 1911, there are three dimensions which are of prime importance other than the spring constant. They are the free length, the installed length, and the fully-compressed length. The difference between installed length and free length can be called X1 and the distance between fully compressed length and free length can be called X2. When the action is closed, the force tending to keep it closed will be the recoil spring constant times X1. When the slide is drawn fully back, the force trying to return it will be the spring constant times X2.
The length of the spring does not affect the spring constant. Making a spring with the same number of coils, wire diameter, and outside diameter but with a longer free lenght (or permanently stretching one) only changes X1; this causes the force at the installed length to be higher, but it does not change the spring constant.
If you cut a couple of active coils off any spring, you will lighten the maximum force since X1 and X2 will be smaller but you will also make the force curve peakier because the spring constant will be greater.
Work is force times distance or: integral F(s)ds. If you plot the function of force versus distance the area under the curve will be this integral. Since the spring is a linear device, the area under the curve is a triangle and the area of this triangle is one half the ordinate times the abscissa. Since k.X is the force of a spring, the potential energy of a spring (the work absorbed by it) is 1/2 k X^2.
The energy absorbed by a recoil spring when the slide moves from fully closed to fully open is = 1/2 k ((X2^2)- (X1^2)) .
This is equivalent to subtracting the area of the triangle associated with the installed compression of the spring from the area of the triangle associated with full compression of the spring.
Only a small percentage (about 20%) of the kinetic energy of the load can actually be absorbed by the recoil spring, a part goes to work the hammer and compress the main spring, some is lost to friction, and by far the larger part of this kinetic energy goes to impact the frame (again a small percentage when the barrel's lower lugs hit the frame in recoil, and a the larger part at the end of the rearward travel).
At the moment the gun fires (slide and barrel recoiling about only .10") actually very little energy is absorbed by the recoil spring.
I know this is a long and unsolicited explanation and all of you know I'm just a humble aficionado, so please be gentle with your comments
!! This is just basic theory but I always want to understand first the basics and then proceed forward, I'll be happy to hear your comments.
 

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Pretty long-winded explanation for something that's self-evident.
 

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TiroFijo,
Thank you for sharing the technical side of how springs function, amigo. There are some of us who read Gunsmithing Talk who appreciate learing something new about how our pistols work. Despacio Gato
 

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I've been building, shooting, collecting 1911 pattern guns for 27 years. I'm an engineer with years of experience working with math on a daily basis to solve problems & I don't think I see it as "self evident" that a spring works in that particular manner. I ALWAYS appreciate the opportunity to learn something new or see something in a new light. Thanks Tirofijo for your time and trouble to explain this concept. Now I just have to digest it.


[This message has been edited by BBBBill (edited 10-27-2001).]
 

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Hello TiroFijo,
Thanks for the great technical brief on the recoil springs. I had always thought that springs were linear also, but many recoil springs are advertised as 'variable power' .. What is the meaning of that specification ???
Please excuse my ignorance: is not 'self evident' to me.

Regards,
 

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Discussion Starter #6
From the Wolff gunsprings web site: http://www.gunsprings.com/1ndex.html
"1. What is the difference between conventional and variable recoil springs?
The difference is both physical and operational. On a conventional spring, all the coils are spaced equally apart, except for the closed ends. In a variable recoil spring the space varies between coils with less space between coils at one end and more space between coils at the other end. The way the springs store energy is also different. For example if a conventional recoil spring is compressed 1/2", it might store 1 pound of energy. For every additional 1/2" this spring is compressed it would then store 1 additional pound of energy. When a variable recoil spring is compressed 1/2", it might store 1/4 pound of energy. The next half inch of compression might store 1/2 pound, the next half inch might store 3/4 pound and so on. In other words, a conventional spring stores energy on a straight line and a variable spring stores energy on a curve. If both springs are rated at 16 pounds, they will both store 16 pounds when compressed to the same working length, but the way they get to 16 pounds is different."

"2. Should I use a conventional or variable spring when both are available?
The choice is often very subjective. Variable recoil springs reduce the battery load values with increasingly greater recoil load values. This results in easier unlocking, improved recoil energy storage, dampening, feeding, breaching and lockup. Variable recoil springs are particularly beneficial with compensated pistols and when using light target loads where less recoil energy is available. Conventional recoil springs are particularly beneficial when shooting heavier loads where keeping the slide closed as long as possible is desired. The "correct type" of recoil spring is best determined through experimentation and your own personal preference."

Variable recoil springs are generally used for compensated pistols, because the muzzle break/compensator "steals" some recoil energy at the moment the bullet leaves the muzzle (which is moment just previous to barrel/slide unlocking in a well timed pistol). Therefore, at this initial stage you want a "softer" spring, but you also want this spring to become "stronger" as it compresses to cushion the slide and to have enough energy stored to feed reliably in the returning stroke. Normally a variable spring stores less energy than a conventional constant spring of the same rating.
 

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Thanks TiroFijo, heavey duty post, you cleared-up some stuff I thought was threory, thank you for sharing, Pete


------------------
Metal Smith

The only thing I know for sure is what I can measure!
NRA Life Member
 

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TiroFijo,

Thank You Very Much !!!!!!

Please continue to post such great information. I plan to file them for reference.

And from your information, I may just go back
to Conventional since I shoot 230gr factory
only....

Best


[This message has been edited by SouthGun (edited 10-29-2001).]
 

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Discussion Starter #9
Thanks a lot for your comments, with due respect, if all this is self evident either you are a genius or you are not paying enough attention
!! In very general terms the principles of the 1911 operation are “easy to understand”, but when you get to the details you realize it can get quite complicated.
I don’t have much experience building, tuning or repairing 1911s, and any of the top class gunsmiths or competitors that frequent this forum would be a much better choice for that kind of information. I do have some basic technical knowledge about 1911 dynamics, and the purpose of this post is just to clear some basic notions and elicit some discussion and comments from the many knowledgeable members of this forum. Hopefully we could get to discuss spring rates in a more practical context in future posts.
When you install a new spring into your pistol sometimes you have to cut it a little so the coils don’t touch each other when fully compressed. As mentioned before, when you do this, you are lightening the maximum force (or “spring rate”) because X1 and X2 are smaller, but you are also making the spring constant greater (check the formula).
Using the formula for conventional coil springs:
Material = steel spring, outside diameter = 0.435 inch, wire diameter = 0.045 inch, number of active coils = 31.
Constant rate k = 3.23 lb/in
Free length = 6.780", X1 = 2.933", X2 = 4.973"
Spring rate = k*X2 = 16 lbs.
If we clip two coils, its new free length would be 6.343”, X1’ = 2.496", X2’ = 4.536"
Constant rate k’ = 3.45 lb/in
New spring rate = k’*X2’ = 15.65 lbs.
Still very close to the original, but please don’t overdue this
!!
The coil spring wire works like a torsion bar, if you make it shorter you are also making it more rigid. The new coil springs with rectangular cross section wire are more efficient than the round wire ones because the rectangular shape is better at resisting torsion than the round section. If properly designed they can outlast round wire ones, but normal springs are more than good enough, so don’t worry too much about it.
 

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OK then.The next time a customer brings me a semi-auto and says "it slams the slide back real hard and flings the brass about 20 feet",I'll know what to do.

Instead of relying on my 23 years experience as a gunsmith,I'll 1)go to MIT and get an engineering degree.2)sit down with a pad of grid paper,a bunch of pencils,and a calculator.3)spend several hours calculating up a storm,so I can tell the guy "the spring-rate of you recoil spring has deteriorated to such a degree that you will require the acquisition of a new one."

Yeah,that's the ticket!
 

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Rocklobster, you're kinda new around here. FYI, there is no reason to be arrogant or difficult to get along with. Information was presented that may just be of some use to someone here, whether in a purely conjectural context or possibly in grasping a concept by coming at it from a different direction. As a commander in the military, I told my NCOs and junior officers to never treat the men as if they were stupid. Give them encouragement to speak up when thay had a good idea ( and at the appropriate time of course). My commands were successful due to the fact that my men knew that they were respected. They in turn made me look good. That concept works just about everywhere in life. Try it out. It might work for you too.
 

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Rocklobster,

Kuhnhausen seems to have done alright explaining the technical side of things. His books are pretty wordy too.

Do you have a problem with understanding WHY something works, and the reasons behind it?
 

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Hello TiroFijo and RockLobster,

Having an enginnering background, I find it easier to understand the theory of mechanical functioning. An 'intuitive' approach will often prevail when the formulas don't work, but that takes the experience gained from years of hands on work.
As a beginner, I feel it is beneficial to learn how it is 'supposed' to work, and then gain the wisdom that embellishes the theory.

Best
 

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TiroFijo,

On a related topic, there seems to be a heated division of ideas on MainSprings...

My gunsmith felt the action on my 1911 and then told me to clip 2 turns off the stock coil to lighten the pull and reduce the chance for hammer fall on a dry slide drop. Others seem totally opposed to this idea... Any thoughts on this ??

Thanks for your most knowledgeable posts.

Regards
 

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SouthGun,
Clipping coils from any spring is an amateurish way to modify the spring rate.
If you are dealing with a 'smith who is advising this, find another one.
 

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Discussion Starter #16
Rocklobster, you are right, you don't really need to know all these tidbits to be a good gunsmith, in fact I'm pretty sure JMB did not work out theoretically all the details of dynamics and physics that make his guns work so well. The original purpose of this topic was just to understand how coil springs work, I guess there is nothing wrong with that or we would still be relying on intuition to design things. If this is too technical, or boring, or you already know all this feel free to leave, or better yet, stay with us and give some valuable information to SouthGun.
On clipping springs: many competition shooters play a lot with their recoil spring settings, and they often buy springs made specifically so you can clip a few coils to experiment. There is nothing wrong with that as long as the springs were made with this purpose in mind and you have the necesary expertise. Generally speaking, unless you are very experienced, don't touch any of your springs, specially the hammer and sear springs.
Most of the time you can not tell if a spring is fatigued just by measuring it and performing the calculations I mentioned. This is because the external area of the wire (the part that is most subjected to tension) looses its elastic properties (G degrades). You must check by feel or with some means of measure, or just diagnose from fuctioning characteristics.
 

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Yikes, well, o.k. here I go offering an opinion in the august presence of guys who are professional pistolsmiths.

I design springs for a living. Well, sorta, I now run a spring factory. In any case I've been an engineer in the spring business for seventeen years(mostly automotive springs), and have a liking for 1911's as well - one of the greatest mechanical masterpieces ever devised.

TiroFijo, I compliment you on your contributions - spring design is an esoteric subject that most engineers don't understand as well as they think. I still get surprised by the darn things every so often.

Let me try to give some simple explanations - they have worked for me when explaining springs to laymen in the past.

Spring "load" is the force required to compress the spring to a given length.

Spring rate tells you how the load changes as the length changes.

I once for fun calculated the spring rate on a 1911 recoil spring, got a number nothing like the rating, and wondered if it wasn't the installed load. Thanks, Tiro, you confirmed my suspicion.

Please note that the spring rate is, within reason, independent of the free length of the spring.

How do you tell if a spring is "worn out" ?

Easy, measure the overall length when it is new, in the free (disassembled) position. Record that length. After shooting a while, disassemble it and re-check the length. If it hasn't changed, it's still producing just as much force as when it was new.

If your used spring has gotten shorter("taken a set"), it's now producing less force when installed. How much set is too much? When the gun quits working, silly!

Even if it still works o.k., I would still probably replace a recoil spring after 5000 cycles or so, especially on a gun used for defense. You never know when a small defect will grow into a fracture, and recoil springs live a pretty hard life.

Hope this info is helpful. Other spring questions, feel free to throw at me.

------------------
Patrick
 

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TiroFijo,
Thanks for the info, I found it very interesting as I do most of the stuff written here.
Thanks
Ed
 

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Originally posted by TiroFijo:
Hola amigos, spring rates sure is a popular topic, but apparently most people are confused about what is a "spring rate", <snip>
I know this is a long and unsolicited explanation and all of you know I'm just a humble aficionado, so please be gentle with your comments
!! This is just basic theory but I always want to understand first the basics and then proceed forward, I'll be happy to hear your comments.
Thanks! I just learned a whole bunch, and after going to the wolf site learned even more, thanks for the time you took to post all that, I'm a newbie and learned alot from this post!
 
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