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What "simple physics" is that?

F=-kx has no time dependency.
Not trying to be scientific here. I was simply making a common phrase in speaking generalities about steel. However, with my observations from my experiences with steel, it may not have a scheduled time of it's engineered design's demise, but time is not on steels side. Many variables can expedite it's demise and in the environment of the saxophone it is placed within an area that is not always so kind to steel. Water, aka saliva, even worse possibly, increases its slow process of no longer being steel.

I have a background of classic car restoration and it has always been my observation that old springs no longer hold the tension they originally were designed to hold. A common term used for steel when it is fatigued in an automobile spring is 'sag'.
 

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retensioning a spring is possible, but breaking an old spring while doing this is also easy.

My friend’s horn was beyond re-tensing and all the springs needed changing but you cannot generalize. My Super 20 has all functional springs and they are 50 years old.
 

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What "simple physics" is that?

F=-kx has no time dependency.
I was wondering about that, too. Hooke's law has proven to be timeless :)

However, here is a (probably dumb and only hypothetical) question: Is it possible to re-harden springs by heat treatment if they have been bent past the elastic limit? I would think it might be possible but the spring won't have the original strength. Thanks!
 

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You know, I don't understand this.

It's well known that leaf springs on old cars will sag over time. Surely the springs are designed so that even at the bump stops, they're not stressed past the elastic limit. Common metallurgical knowledge says that the spring constant remains constant, unless you are in the last stages of high cycle fatigue and you've got a fatigue crack that's progressed so far that the stress area is reduced - but at that point you're just a few cycles away from final failure.

So what actually happens in those automobile leaf springs, that one big impact clear down to the bump stops doesn't cause plastic deformation and subsequent sagging; yet hundreds of thousands of smaller impacts and a few big one do?

As to hardening, when you bend a steel spring past the elastic limit, you're not going to need to re-harden. If anything it would have slightly work-hardened. So if a spring has been deformed by over-bending it you should be able simply to re-bend it to the correct shape.
 

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You know, I don't understand this.

It's well known that leaf springs on old cars will sag over time. Surely the springs are designed so that even at the bump stops, they're not stressed past the elastic limit. Common metallurgical knowledge says that the spring constant remains constant, unless you are in the last stages of high cycle fatigue and you've got a fatigue crack that's progressed so far that the stress area is reduced - but at that point you're just a few cycles away from final failure.

So what actually happens in those automobile leaf springs, that one big impact clear down to the bump stops doesn't cause plastic deformation and subsequent sagging; yet hundreds of thousands of smaller impacts and a few big one do?

As to hardening, when you bend a steel spring past the elastic limit, you're not going to need to re-harden. If anything it would have slightly work-hardened. So if a spring has been deformed by over-bending it you should be able simply to re-bend it to the correct shape.
Thanks, and good point. Here is a paper describing the development of spring fatigue:

https://www.sciencedirect.com/science/article/abs/pii/S135063071831611X

In short, micropits develop in contact areas and through corrosion that will eventually result in micro fractures or cracks, which continue to get worse until failure.
 

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Thanks, and good point. Here is a paper describing the development of spring fatigue:

https://www.sciencedirect.com/science/article/abs/pii/S135063071831611X

In short, micropits develop in contact areas and through corrosion that will eventually result in micro fractures or cracks, which continue to get worse until failure.
Yeah, but that's just a deeper dive into the mechanism of high cycle fatigue failure in vehicle coil springs. It says nothing about how "springs sagging" which does really happen, occurs. That is a completely different phenomenon. Basically it appears that repeated stresses that seem like they should be well under the elastic limit, cause permanent deformation.

And a third phenomenon which may or may not exist is a change in spring constant over time.
 

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Yeah, but that's just a deeper dive into the mechanism of high cycle fatigue failure in vehicle coil springs. It says nothing about how "springs sagging" which does really happen, occurs. That is a completely different phenomenon. Basically it appears that repeated stresses that seem like they should be well under the elastic limit, cause permanent deformation.

And a third phenomenon which may or may not exist is a change in spring constant over time.
That's where I am not sure. I read up a bit in between and sagging has been attributed to the progression of micro cracks found using electron microscopic examination of springs. Honestly, I don't know enough about this and a crash course in reading materials is not always a substitute for real knowledge and understanding but it sounded pretty plausible. And it was on the internet ... :)
 

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My NA (S# 272... is actually my main alto so yes, I know what you are talking about. And they moved away from the split bell. Among the 10+ altos that eventually gravitated here, this is my favorite (aside from my 6M but that one is in factory new condition and I only play it on a blue moon). Built like a tank and an incredible sound!
Nice! Shame the way altos go gravitating to one place. You would think they would want to be evenly distributed, but I've got a tangle of them too.

Yes, I was wondering, however, if there had been any TTs with the Norton springs since they were introduced in 1931 whereas the NA only came out in 1932. Most likely not because AFAIK the S# refer to the date of sale rather than manufacture so it is possible that the early NAs were indeed made in 1931 coincident with the introduction of the Norton Springs. But that was really what my question was aimed at.
For a while I was very into Buescher brass instruments and in the process of sketching out the development of various model lines I came to the conclusion that Buescher had a habit of springing new models on an unsuspecting public and only then bothering to name and describe them in catalogs. It wouldn't surprise me if they started shipping NA horns before they showed up in official publications.
 

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That's where I am not sure. I read up a bit in between and sagging has been attributed to the progression of micro cracks found using electron microscopic examination of springs. Honestly, I don't know enough about this and a crash course in reading materials is not always a substitute for real knowledge and understanding but it sounded pretty plausible. And it was on the internet ... :)
OK, well, I didn't read the paper linked to due to a paywall.

I think it's plausible that the progressive development of microcracks could progress in such a way as to lower the modulus of elasticity, which would be a different phenomenon than microcracks progressing to high cycle fatigue failure. More reading of the literature would be indicated.
 

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It's much easier than that, the pegs are soldered into a little center hole in the cup, if you heat it up, they come out without damage. I had this happen on one of the TTs I just did, accidentally overheated a little with the electric heat gun and the peg came out, and it was just as easy to put it back in, only thing I added was a little flux and it fell right into place again. [ . . . ]
Was this the 1925 horn?

Sometime between '26 and '29 they started mounting the spud on a smaller plate than before, and I think they're silver-soldered in after that point, and thus harder to casually de-solder. Here's a pic of a side-C from from two alto horns, on the left from a '29 horn, the right from a '26 horn. You can see the base of the spud on the '29 key is much smaller than on the '26 key. The '29 key is larger in diameter, too.

 

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Was this the 1925 horn?

Sometime between '26 and '29 they started mounting the spud on a smaller plate than before, and I think they're silver-soldered in after that point, and thus harder to casually de-solder. Here's a pic of a side-C from from two alto horns, on the left from a '29 horn, the right from a '26 horn. You can see the base of the spud on the '29 key is much smaller than on the '26 key. The '29 key is larger in diameter, too.

Yes, that is the 1925 horn. Very interesting, and this certainly also explains why a TT pad set may not actually work on some of them. I have two 1925 and one 1924 and they appear to be identical. I have also possibly access to a Harlow & Jenkins stencil of the same time frame that I could check.
 

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Yes, that is the 1925 horn. Very interesting, and this certainly also explains why a TT pad set may not actually work on some of them. I have two 1925 and one 1924 and they appear to be identical. I have also possibly access to a Harlow & Jenkins stencil of the same time frame that I could check.
There are a number of gradual keywork changes in the TT horns from the time they added the crescent G# & front F to the introduction of the NA line, but this is the first time I've noticed a difference in pad sizes. Now I wonder how much those changed during that period. I've measured the key cups on the '29 horn and a mid-'30s Aristocrat and they were identical except for the bell Bb.

It makes sense they went with a larger diameter for the side-C, the pad on the older one is barely wide enough to cover the tone hole. Assuming they didn't also widen the tone hole in the later horn, which I didn't measure!
 

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... Basically it appears that repeated stresses that seem like they should be well under the elastic limit, cause permanent deformation....
On a motor vehicle a spring perhaps suffers from impact forces at times, which may cause the sag. Just guessing here. Otherwise the sag is surely from the microcracks that have not yet resulted in breakage.
After all, the stiffness of a flat spring is proportional to the thickness cubed so microcracks that compromise the effective thickness would have quite an effect.

... I think it's plausible that the progressive development of microcracks could progress in such a way as to lower the modulus of elasticity, which would be a different phenomenon than microcracks progressing to high cycle fatigue failure...
During my formal engineering study I was astonished at the massive number of of cycles a spring had to endure before cycle fatigue was significant.
I doubt that musical instruments would get there.

BTW clearly, somer manufacturers in the past have established much lighter springing than others. Perhaps this is being incorrectly called fatigue.
 
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