A solution for springs that are too stiff

[jbtsax]

I don't know if any of the other repair techs have encountered this problem, but I have found on many vintage saxes the spring on some keys is too thick to function properly and give the proper "feel" to the key.

The worst offenders are usually the F# key, Bb bis, and the Eb trill key on older models. The problem is that these are "secondary" springs that open a key, but must be overcome by a "primary" spring. Excellent regulation is impossible when these springs are out of balance or maybe proportion is a better term.

The case in point is a Buescher True Tone curved soprano I am restoring. The spring on the F# key is much too thick and stiff. Some of the common remedies are:

-Fill in the spring hole in the post with solder and drill a smaller hole to accept a spring of a smaller diameter. This fix is only possible when there is clearance to drill a hole on the correct axis to the stack.

-Use a smaller spring and force a short piece of spring into the hole with it to make it snug. I don't care for this remedy because it can look amateurish, and it is not easy to do.

I came up with a process to take the spring size that fits into the hole when dovetailed and to turn down the portion that extends past the post to a smaller and more flexible diameter.

First I chucked the spring into a cordless drill to have just the portion of the spring past the post exposed. Then I made 3 or 4 passes with the spring turning the opposite direction as a sanding disk in the bench motor. This needs to be done smoothly and lightly because the metal is removed very quickly.

The next step was to smooth and polish the spring by spinning it in the bench motor and using 400 grit followed by 1200 grit sandpaper.

This view is the needle spring after reducing the diameter of the end.

This shows the spring after bluing, cutting to size and dovetailing

Here is the spring installed on the saxophone. It was originally .032" and taken down to .025" diameter. It gives a much better feel to the F# key which will make regulation much easier to do.

 

[MartinMods]

I like to use (turn against) a diamond block for the initial cutting.

 

[jbtsax]

I like to use (turn against) a diamond block for the initial cutting.

Doesn't that take a long time?

 

[SOTSDO]

A concern to consider...

Spring stock is made by forging the metal - forcing it through roll stands or between a hammer and a die, all while the stock is heated to red heat. This is what makes it "tough" compared to regularly finished metal.

Although the process is brutal (you are, after all, smashing the metal between two harder surfaces), it does tend to give it great resistance to fracture failures, which in turn is a big positive in a spring.

Reducing the diameter through an abrasive process (for that is what is being done here) would tend to remove some of the properties that make a spring a spring. No matter how careful the "turning" and finishing is done, abrasives like carborundum or diamond remove their "turnings" by scratching/scraping away at the surface of the spring, and in doing so introduce tiny irregularities in the surface of the spring metal.

I have no doubts that the spring, as modified, is serving its purpose now in a wonderfully adjusted fashion. My concern is for long term use. Every metal part on a musical instrument serves some sort of dynamic purpose, with stresses being thrown into them as the key work is manipulated by the player. Springs are, in effect, the points where the greatest stress is introduced into the "system". And, over the typical working life of even a student instrument, stresses are pumped into a spring many thousands of times.

I would imagine that it's too much trouble for a repairperson to test where the yield point is on such a spring - i.e., how many flexes it can take before failure. And, maybe I'm just over-worrying this whole thing.

But, I've seen too many failures on industrial springs from some pretty weird circumstances (like sandblasting rust off of them, only to have them fail in a year or so) to completely dismiss my "theory" here. The main difference is that, when those failures occurred, somebody died; when a horn's spring fails, it's a trip back to the repairman.

 

[jbtsax]

Your point is well taken Terry. I realize that this process weakens the spring somewhat. In a few trials using this method I manipulated the springs to try to force them to break, in essence to see what I could get away with. I found that "tapering" the removal of the metal from the post area to the tip produced a lighter spring with more structural integrity.

In repair most things in the end amount to a compromise of one type or another.

What I would really like to find is something one could dip the end of the spring in to coat it to a larger diameter, without removing the temper by using heat. Any ideas on this approach would be appreciated.

 

[MartinMods]

But, I've seen too many failures on industrial springs from some pretty weird circumstances (like sandblasting rust off of them, only to have them fail in a year or so) to completely dismiss my "theory" here. The main difference is that, when those failures occurred, somebody died; when a horn's spring fails, it's a trip back to the repairman.

I know what you mean, but I'd hesitate to make such a direct comparison of sandblasting of rusted spring steel for critical use with precision grinding/polishing/hardening/tempering of healthy spring steel. I think rust damage was perhaps the culprit in the former.

 

[SOTSDO]

Rust damage = notching

We tested the rest of the springs in that case, and the testing lab found that the notching effect from the sandblasting was the proximate cause of failure. Similar springs with rusting still intact failed at approximately 50% more load (as I remember it).

(One of the wonderful things about my former employment was that (once there was blood on the ground), employers were willing to spend money like water to do lab testing on stuff. Saved you, the taxpayers, a bucketload of money.)

Push comes to shove, I'd test my technique to destruction before I did this to a pile of 'em.

 

[Steve]

I do about the same thing .. well, I guess nearly exactly the same thing. Some older clarinet spring cradles are super small for the tip of the spring. And over the years after a couple spring replacements the post hole is slightly enlarged, thus the only real solutions are the ones mentioned. sanding down the spring actually is fairly fast and accurate for me.

 

[clarnibass]

How do you re-blue the spring?

I have done the same thing a couple of times, with the only difference being micromotor and lathe instead of drill and bench motor.

 

[Steve]

fyi, I also do most of my bench motor work on a wood lathe. I've just found it easier and I have a lathe drill chuck etc for it. So I also would cut /shave down the spring on my wood lathe with a drill chuck head and basic files.

 

[jbtsax]

How do you re-blue the spring?

Sportsman's shops in the US have bottles of bluing used for guns. I have had varying success using it. The metal must be very clean. It does not work on stainless steel. The hard part is making it shiny again after the bluing without taking most of the bluing off. Steel wool works the best for me.