Why the switch to a coil main spring ?

[SmithSwede]

I know the older S&W .32 Hand Ejectors used leaf style mainsprings, but then that design was replaced with coil type mainsprings for the improved I-frame and later J-frame.

Anyone know the engineering reason why this was done?

After all, the older revolvers prove that a leaf spring will work just fine for such a small mechanism. I’ve never heard problems with the leaf springs breaking. So a coil spring doesn’t seem essential for the design.

I’m not sure cost-cutting was the reason either. If cost was the issue, then why didn’t S&W switch to coil springs for the other frame sizes, like K, L, and N? I think cost considerations drove elimination of “pinned and recessed,” the other frame screws, etc., but that cost-saving design change was applied to all frame sizes, not just the J.

Seems like I’m missing a piece of the puzzle here.

 

[SweetMK]

engineering reason,,,,,,,,
For a given space,, a coil spring will do the "spring thing" more efficiently,, as compared to a leaf.

Why do they use a leaf??
probably because space is not a premium,,,,,

You do not see leaf springs involved with the trigger return??
If it were a leaf,, you would need King Kong sized hands, to reach around the leaf,,,

 

[gwpercle]

Space ... the coil spring simply takes up less space in the J-frames smaller grip frame ... it works more better ...
Gary

 

[murphydog]

And eliminated an extra machining process for the opening for the strain screw, and the screw itself.

 

[desi2358]

A coil is compact and simple, does the job quite well. S&W could have switched the larger frame guns over too, after all Ruger and others have used coil springs in full sized guns for years. I always figured it was at least partially a cost issue with the small frames. Especially when you look at the changes over time such as replacing the round headed rod with the simple stamped spring rod (which also eliminated machining the round seat in the hammer for a simple slot and cross pin).

Having made a few leaf springs over the years for muzzle loaders and various other old guns I know that leaf springs take a bit more work to make. Even when done in large lots on a production basis this is still true. Really, I find it kind of surprising that S&W hasn't switched all their revolvers to a coil mainspring. At a guess they simply haven't felt the need as long as the tooling still works and they have qualified people to run it.

 

[rct269]

I was just going to say, "Because it works more better.", and let it go at that. Some of these folks before me did a better job.

As to cost cutting, that motivation had not yet arrived---their motivation at that time being to build the best possible product for the price---as it had been since 1857-----thereabouts. The concept of doing better by building the product at the lowest possible cost came along a little later, and based upon the moaning, groaning, fussing and fuming about poor service and lousy quality control we see here on a regular basis today, it's going full tilt boogie now!

Damn shame too!!

Ralph Tremaine

 

[walter o]

If i am not mistaken the model M original lady smith used leaf springs
so size would not be a problem .I think that N,L,K frame guns have a better trigger than you can get on a J frame .
As to As a trigger return spring S&W used a leaf spring on the early hand ejector ,but had to use a set up to turn into s rub Goldberg arrangement.So they changed to a coil spring and a sliding block.Back then they all (companies ) were trying to find the best way to make a useful tool(gun).
Looking at the progression (development )of S&W firearms is a interesting experience in its self

 

[Green Frog]

There was an extensive discussion here about a decade ago, and the general consensus was that the leaf spring allowed for a superior trigger poll and that no matter how good the coil spring there was always a certain level of “stacking” present. I think it’s safe to say the change was financial rather than as an “improvement”. If I could have had the choice of a leaf spring on my J frame guns I would have! YMMV.
Froggie

 

[glowe]

The 1896 32 HE, the Model 1899 and 1902 K frames had flat springs operating the trigger, as well as the flat mainspring for the hammer. My guess is that almost all examples of these 120+ year-old revolvers still have their original flat springs. The perineal goal of manufacturing is to constantly try to lower costs, while maintaining acceptable quality. Flat springs cost more than coil springs, so my guess is that's the main reason why companies changed to coil springs was to save money.

Coil springs offer increased resistance as they are compressed, so not nearly as even tension as flat springs. Flat springs are normally designed so they do not flex a great deal, giving a more even cocking tension than coil springs. I suppose if the coil spring is lengthened, it would also offer a more uniform hammer pull as well. That, however, might defeat their main advantage of being cheaper to make.

 

[2152hq]

If a single leaf flat spring, or V style flat spring is designed and shaped correctly along with the right geometry of the part(s) it is imparting motion & the leverage of the system ,, the tension or pull can be made to be the heaviest at the beginning of the cocking motion. Then the effort substantialy lowers as the hammer comes back to full cock.

Finely made English sporting Flint Locks often have this excellent operational feel.
A very simple US made single shot of early manufacture that also exhibits this feature was the Stevens Tip-Up single shot rifle.
The latter not having the excellent hand fitting of the parts and the mainspring usually showing no fitting what so ever other than a quick swipe off of the end that contacts the hammer for a good fit. But the feel of the leverage principle of heavier pull first then reducing down to a much lighter cocking effort is easy to feel. Makes the Sear to Hammer contact least of a strain then and a better trigger pull can be gotten from it.

A lot can be done with a simple flat spring to improve it by reshaping the arm(s). It can also be ruined by the same process if the 'smith doesn't understand what should and shouldn't be done to them as far as shape.

Coil springs are cheap and easy to mfg'r.
They can keep on working even if they break somewhere in the line of coils if the spring is equipted with a follower or is captured in a guide hole.

Dirt and dried oil can stall them.
Lots of V springs are broken during dis-assembly/re-assembly and not by simple use.

Cast flat springs of today seem to be OK. They need to be polished to a fine surface and shaped just as a forged or machined one.
No shortcuts there or in a proper hardening and draw.

Lots of small flat and V springs today are mearly punched out of spring stock and again punch pressed into the desired shape.
Late Colt DA revolver mainsprings for the old style DA revolvers were stamped production.
Another mfg'rs $$ saver.

 

[Green Frog]

Well if you want to compare leaf spring action to coil spring in a rifle, you need look no farther than the Winchester high wall. From 1885 to about 1908 they used a leaf spring, both to hold the lever up when in place as well as to power the hammer. After 1908 they began using a complex coil spring until production ceased in the early 1920s. In the standard Sporter model, the trigger was much more easily tuned with a very little judicious stone work on the leaf spring along with the usual work on hammer, sear and trigger. Of course it was a fairly complex lock work, so there were lots of tricks, even without set triggers. Once single- and double set triggers were developed, the advantage mostly disappeared, and the more durable coil springs got the job done just as well. Having worked with both, if I’ve got DSTs. I’ll take a coil spring action, thank you!
Back on topic though, any advantage in durability is lost, IMHO at least with the simpler J frame lock works and the simple trailhead action of the spring, leading to stacking. YMMV.
Froggie

 

[rct269]

As somewhat of an aside, both the U and W springs available for N frames (at least?) served both the hammer and trigger needs (doing away with the coil spring inside the (trigger) rebound slide). To the best of my knowledge, neither the U or W springs were used in regular production; being available only as what I'll call an accessory item. I tried both in a Highway Patrolman.

The results were akin to those achieved today with a spring kit---significant improvement in D.A. trigger pull---not much difference in S.A..

And speaking of spring kits, Miculek's is the only one I've tried, and the improvement was ASTOUNDING!! Perhaps the best part about it is you can end up with whatever D.A. pull you want, although he cautions against going below 7 lbs.---and recommends using Federal ammo/primers at that level. The one note of caution is READ and FOLLOW his instructions!! I didn't, having no need for instructions to replace two springs; and NOTHING would move when I finished. Suitably enlightened, I started over---first with the instructions---and everything was fine the second time around!

Ralph Tremaine

 

[JH1951]

...............................
And speaking of spring kits, Miculek's is the only one I've tried, and the improvement was ASTOUNDING!! Perhaps the best part about it is you can end up with whatever D.A. pull you want, although he cautions against going below 7 lbs.---and recommends using Federal ammo/primers at that level. The one note of caution is READ and FOLLOW his instructions!! I didn't, having no need for instructions to replace two springs; and NOTHING would move when I finished. Suitably enlightened, I started over---first with the instructions---and everything was fine the second time around!

Ralph Tremaine

My father would often say "If all else fails, read the instructions."