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Old October 28, 2017, 09:14 AM   #1
redlightrich
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A discussion and questions about coil type springs

Hello all, in an effort to tune my CZ PCR with Kadet 22lr kit, I am forced to ponder coil springs and their effect, and how they respond to modification, specifically clipping off coils.
I have recently been working to make this pistol feed CCI SV40g ammo reliably. It becomes clear that the SV ammo doesn't have the power to fully cycle the slide.
This kit runs 100% with HV ammo of any brand I tested, which is about 10 different types. Due to the fact that many of my other guns run CCI SV, it is a big plus for me to get this to run it also.

My first attempt was cutting 2 coils off the recoil spring. It is a 2 dollar part, and easily corrected if I go too far. Cutting the 2 coils had no appreciable positive effect.
I then installed a 17# hammer spring ( on a CZ compact, factory is 19#), which made it better, but not perfect. It appears that the slide still "short strokes". I have carefully polished all slide contact areas, which made the gun smooth. The polishing was actually the first item I did. The 17# hammer spring has a second benefit of lowering the SA pull a bit.

As I read on the subject, I came across a person who stated cutting coil type spring coils actually raises the rate of the spring? They claim although you are lowering the pre-load on the spring, you are giving the spring a shorter amount of room to compress, which serves to raise it's value? I felt that this statement was a bunch of hooey, but it did give me pause.
This is in regards to my next moves. Do I continue to cut the recoil spring?

I also feel as if I keep lowering the hammer spring rate, I will eventually need to lower the firing pin spring weight as well.

I have just lowered the hammer spring again today to 16#, and will test for reliable ignition and cycling. I also have a 15# standing by, if the 16 has reliable ignition, but I still find short stroke.

Based on the fact that if I load the magazine with 5 rounds ( 10 round mags) I get nearly 100% cycling, I feel that I can get it to run right with more spring tweaking.

As I said, HV ammo cycles perfectly with stock springs. I am trying for perfection when using CCI SV ammo. I also don't want to give up the ability to use HV ammo as well. I need a perfect balance.

If I lower the hammer spring too much, my remedy ( at least as far as I know) is only to play with the firing pin spring. There is no extended FP available, although a lathe could make the pin move further forward.

Reshaping of the pin is always a possibility if cycling clears up, but positive ignition falls off.

Thank you for reading my long winded message which is actually asking " What says ye the experts? Is cutting coils as a way to decrease a springs strength an acceptable method?"

Also, where is there a chart that gives approximate spring strength based on wire diameter, coil diameter and free length? Or is this not enough info to find a value?

Thank you all

Rich
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Old October 28, 2017, 12:51 PM   #2
45 Dragoon
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No, cutting coils reduces the working length of the spring. Reducing the diameter of the spring material is how you properly reduce the strength of a spring.

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Old October 28, 2017, 02:00 PM   #3
Jim Watson
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Have you polished the firing pin stop and hammer face? Reduce friction against the slide camming the hammer back.
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Old October 28, 2017, 02:07 PM   #4
ShootistPRS
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Coil springs are torsion devices that are curved, Compressing a coil spring makes the wire twist and that is where the springiness comes from. Cutting coils shortens the torsion length so it becomes harder to twist. You can reduce the compression rate by having more coils in the same length (effectively lengthening the torsion bar) or by using smaller wire with the same number of coils and length.
Another aspect of coil springs is that the coils are usually wound tighter (more coils per inch) at the ends which allow it to begin compressing with less force. Cutting the end off will affect the rate at which it compresses.
Never cut coil springs unless you want a shorter stroke with more force. Even then the load may cause the spring to go beyond its elastic limits and then you need a new spring anyway.
I hope this helps you to understand coil springs better.
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Old October 28, 2017, 08:58 PM   #5
redlightrich
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Thank you all for the replies. Yes, what you all say is what I read elsewhere, but I was having a hard time swallowing that, especially being I hear of people routinely cutting coils off springs.

The good news is the replacement springs are only 2 dollars

I have been reading of people having no problem using the Kadet kit with SV ammo, however, most everyone else is using this on a full size 75.

This project is for a compact. The compact and full size use the same main spring, ( although the full size is 20#, while the compact is 19#) also, the hammer strut is different. I wonder if the strut could contribute to the issue?

Thanks again
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Old October 29, 2017, 12:17 PM   #6
T. O'Heir
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"...reduces the working length of the spring..." That reduces the amount of pressure it takes to contract the spring. It's one of the things done in a poor man's 1911 trigger job. Two coils is way too much though. Half a coil is done on the poor man's 1911 trigger job.
"...the same main spring..." You won't notice the difference of 1 pound. However, on a .22 it's very easy to reduce the spring to the point the trigger is unreliable. Better to buy proper lower powered springs. Contact Wolff Springs. http://www.gunsprings.com/
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Old October 29, 2017, 12:24 PM   #7
ShootistPRS
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T. O'Heir.
If you take a torsion spring - a straight rod - that is 12" long it will twist easier than if you cut it to 10" long. It doesn't reduce the amount of pressure to twist it. The same thing happens with a coil spring which is a torsion spring that is bent into a coil. The wire in the spring twists as it is compressed. That makes it a torsion spring. I suggest you either actually test it with a good measuring device or study what makes a coil spring work.
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Old October 29, 2017, 04:37 PM   #8
BOOGIE the oily
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ShootistPRS and 45Dragoon are dead on.
There are 2 ways you can "properly" lighten a spring: adding coils (getting a spring with more coils of the same wire gauge), or getting a spring made with thinner wire. You could also use a bigger diameter spring (if you have room) to the same effect. Both that and adding coils soften the spring by providing a longer piece of wire to be twisted.
Then there are some "not-so-proper" ways to do it, like carefully sanding the wire to make it thinner, which could render fairly good results, depending on how careful/skilful you are (but which I wouldn't use on a firearm, and I definitely don't recommend you to).

Quote:
Originally Posted by redlightrich
My first attempt was cutting 2 coils off the recoil spring. It is a 2 dollar part, and easily corrected if I go too far. Cutting the 2 coils had no appreciable positive effect.
I then installed a 17# hammer spring ( on a CZ compact, factory is 19#), which made it better, but not perfect. It appears that the slide still "short strokes". I have carefully polished all slide contact areas, which made the gun smooth. The polishing was actually the first item I did. The 17# hammer spring has a second benefit of lowering the SA pull a bit.
Maybe if the slide was short stroking with the cut off recoil spring and the lighter hammer spring, you could try with the lighter hammer spring and a full length recoil spring. Since the full length recoil spring will be lighter than the cut off one, maybe that and the lighter hammer spring would be enough for the weapon to cycle appropriately.
I mean, it's worth a try, isn't it?
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Old October 29, 2017, 08:27 PM   #9
4V50 Gary
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What 45Dragoon suggested. Get a pin punch and insert the spring on it. Take it to a grinder and reduce the overall diameter.
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Old October 29, 2017, 09:28 PM   #10
45 Dragoon
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Exactly Gary! Thanks.
Just use needle nose pliers or something other than your fingers to "contain" the spring on the punch. It's much better than threading a spring into your finger!!
I use a belt sander and the more "askew" you hold the spring (from horizontal), the more material is removed.

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Old October 30, 2017, 02:02 PM   #11
Slopemeno
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Brownells, McMaster Carr, Small Parts and others sell spring stock. Replace the existing recoil spring you're using with a lighter one.

Shortening an existing coil spring really doesn't help.
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Old October 31, 2017, 04:41 PM   #12
ShootistPRS
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Grinding the outside of the spring is a risky thing to do. You have to reduce the diameter a lot to affect the spring strength and grinding makes stress risers in the spring, As it twists it will fracture in those risers and if you put much heat into it the steel will anneal and you won't have a spring. The heat treat temperature of most springs is only 550F.

It is less expensive and a lot easier to just buy a replacement that is correct for your application. You spend more money for lunch at a fast food place.
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Old October 31, 2017, 06:28 PM   #13
45 Dragoon
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Well, I'm probably doing it wrong, but after I get the result I'm looking for, I polish the now tuned spring. That's the way I was taught. Haven't had any break though. My understanding of tuning a S.A.revolver is more tuning what's there than parts replacing. Most of the springs in my business are- flat and tuned, flat and being replaced with a coil, and flat being replaced by a torsion spring that I wind myself (pretty much like a 3 screw Ruger). I find the torsion springs lend themselves to a really fine adjustment and one can create amazingly precise and repeatable setups.

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Old October 31, 2017, 07:23 PM   #14
BOOGIE the oily
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Quote:
Originally Posted by ShootistPRS
Grinding the outside of the spring is a risky thing to do. You have to reduce the diameter a lot to affect the spring strength and grinding makes stress risers in the spring, As it twists it will fracture in those risers and if you put much heat into it the steel will anneal and you won't have a spring.
Exactly! And that's why I said I wouldn't recommend it for a firearm (I should've said "recoil spring").
Not only you create those stress risers, but it's also a practical impossibility to grind the whole spring perfectly even, so you will end up with some coils that are harder than others. Now, that may not be that important on other springs, but with the stress levels a recoil spring works under, I wouldn't risk it.

@45 Dragoon: I've done that kind of jobs many times, and it does work wonderfully. But while doing a hammer spring that way could be perfectly acceptable, a recoil spring has a fairly long (comparing to its own length) travel, and cycles violently. Under those conditions, other phenomena (like resonance, for example) come into play, and can cause the spring to fail.
And, TBH, considering the cost of a spring, I don't see the reason to take such a risk...
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Old October 31, 2017, 08:52 PM   #15
45 Dragoon
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Boogie,
Recoil huh? That's in them "new fangled" guns ain't it? I'm pretty "pigeon holed" with what I work on lol! I can see what you're talking about though. Ruger S.A.s are about as "modern" as I get.

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Old October 31, 2017, 09:19 PM   #16
BOOGIE the oily
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I didn't mean it as an "old vs. modern" thing.
Especially now that Taurus has made a .357 magnum tupperware revolver, I guess that line is getting kinda blurred anyway...
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Old November 1, 2017, 12:42 AM   #17
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A shortened spring (coils cut away) indeed has higher stiffness constant as in Hooke's law. But assuming the same final compressed length, a shortened spring always stores less energy. Hence a shortened spring is always "softer". It asserts less force at the final length, because the "preload" is lower.

However shortening spring is mostly frawned upon as it could change system behavior unfavorably. For instance the higher stiffness constant leads to more "stacking", undesirable characteristics in trigger pull, even the trigger weight is indeed reduced.

Thinning a spring has more "pleasant" characteristics. Preload is lower, and it "stacks" less. It is hence a preferred method taught at gunsmithing schools. I wouldn't worry annealing.

I certainly prefer replacing a spring with softer one if the replacement is available. If not, I cut or thin, depending on situation. Fine to cut a coil off a hammer main spring of a SA pistol, but I will thin the one in a DA revolver. Recoil spring no problem at all. Just go slow. It is hard to add a coil.

-TL

Last edited by tangolima; November 1, 2017 at 12:58 AM.
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