Flat spring sizes or thicknesses for simple system flutes

Irish Flute
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I have been experimenting with making keys for some of the flutes I’ve made from copper and PVC pipe plastic pieces (the copper one isn’t as functional). Currently I am using rubber bands to keep them closed but I’d like to try traditional flat springs. Perhaps even 3d print a key and integrate a flat spring mounting slot into it.

I am wondering if any flutemakers on here have found standard spring sizes and thicknesses from more common instruments (clarinet, sax) that can be easily modified for use on these closed-standing keys. Thanks for any input!

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Clarinet springs would work, the sizes are:

30mm x 2.8mm x 0.4mm for long keys

30mm x 2.8mm x 0.3mm for shorter keys

15mm x 2.8mm x 0.3mm for G# key

You can also trim them to the required length, but the edge needs sanding.

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Ah, are they steel springs, Andy? I tried 0.5mm thick phosphor bronze springs and found them far too weak for flute keys!

I decided I prefer phosphor bronze keys as they are easier to work and won’t rust.

I ended up using 40mm long 0.7mm thick springs for the shorter keys. They come about 2.8mm wide at the end with the rivet hole in, tapering to about 1.8mm at the pointy end. They are still far too long but can be cut off and reshaped easily. I use a little 1” wide belt sander for reshaping.

I also found the ones I bought were too hard and could actually snap when trying to bend them. I partly anneal them, then hammer them lightly on the anvil to produce the degree of hardness I’m happy with.

For the long keys, I couldn’t find my ideal thickness, so just ended up using some 1mm thick sheet phosphor bronze. I cut 26mm wide strips of it on the bench shears.

Then I cut off strips of that 26mm long and about 3mm wide. Then use the belt sander to make them no wider than the key shaft at one end and more or less pointy at the other. I end up snipping a bit off when actually fitting the springs.

Getting leaf keys to work in a nice light and snappy way is quite an art (and some science!). If you don’t get it right the keys can be sluggish and heavy. Happy to talk about that further if it will help.

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Yes they’re steel, nickel plated maybe.

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I know you are in the USA but this UK page gives an idea what is available. Springs for Woodwind Instruments I got phosphor bronze springs for my USA-made flute and they could have been peas from the same pod as the originals. It was a few years ago and IIRC the price was a much less than now - I bought a few extra as spares rather than have to pay postage again.

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On a related issues, Chip, you need also to think about what the tip of the spring bears upon. As you press and release a key, the tip of the spring slides back and forth. This action is enough to wear depressions in the hard timbers we use for flutes. I imagine it would wear poly tube much faster.

On the better made old flutes you find little slips of metal set into the bottom of the key slots for this reason. Metal also reduces friction, assisting in a nice snappy action.

I use little slips of stainless steel, again to avoid rust. The combination of stainless steel slips and phosphor bronze springs seems good.

You’ll be amused at where I source my stainless steel slips. Out of discarded car windscreen wiper blade rubbers! They are about the right width and thickness, and can be cut to desired length using the bench shears.

I use lengths of about 3 to 5mm, depending on which key it is. And I let mine down below the surface of the wood to get the most secure and snappy action.

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I’m reluctant to say something different to Terry, but my Casey Burns flute has phosphor bronze springs running directly on the wood (mopane) and the wood just has a slight polish. The springs come with a spoon shape pressed into the tip which rolls and glides a short distance on the wood. Maybe pillar mounted keys have a different action to Terry’s.

So you might be OK on PVC. If not the wear marks will show where to inset the metal.

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Mopane is good hard stuff, and so it might take a fair amount of time to wear a depression. And, as you say, it will become clear where to insert some metal!

A good thing to do when doing routine maintenance, or if you feel a key is getting a bit sluggish in return, is to grease the tip of the spring to facilitate it sliding. I just use cork grease, and it’s interesting to compare the key snappiness when dry and when greased. It can be the difference between returning and not returning. Worth trying first before messing with the spring pressure.

Indeed, I wonder if the 19th century flutes I’ve found where the keys have dug little holes and no longer operate well have got that way because nobody ever thought to grease the spring tips. I can’t bring any 19th century advice on greasing spring tips to mind!

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All this guidance is greatly appreciated! I reached out to a local woodwind repair guy to see if I could buy a few assorted thicknesses of flat springs from him first before ordering a multi pack online.

@andy_skiff With the steel springs you use, are they difficult to bend them into shape permanently?

Terry, your info on the pieces of metal under the springs is super helpful. I have never actually seen a real keyed wooded flute in person, so I am basing everything I know off forum posts here or various websites like antiqueflutes.com and originalflutes.com. The springs are almost always hidden, even more so anything under them. I had to watch a saxophone repair video on youtube to even understand how these keys work! I will have to see how much the ends rub, it may be negligible.

I am working on a 3d design for a G# key at the moment. I’m trying to make the geometry look nice while making it thicker than most metal keys, for added strength. I’m going to mount this first prototype on posts that are printed onto a plastic ring that fits snugly on the tube. That will allow me to move and turn it to find an ergonomic spot before I drill the vent underneath.

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Woah, you are brave!

You might find some of the images on this page helpful, as it shows the underside of lots of keys.

Most of the old flutes had symmetrical G# key touches, rather like the thumb Bb key. These bugged me, so I came up with an asymmetric key touch. Just to give you something else to think about!

Do come back to us to explain any of the features you see on these keys and springs.

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Yes, that page does have plenty of good pictures to reference from! I have read things on your website multiple times but never stumbled across that page. Definitely has some good pictures showing how close the spring tips come to the fulcrum hole in the key.

I have a question about the shape of the McG# key (clever name by the way). I see in the picture that the touch turns downward, but when you say it’s twisted as well, does that mean the tip of the touch flare away from the body of the flute?

Did the flutes with diagonal G# keys help the little finger stay on better? Like this one

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Yes, that proximity of the spring tip to the fulcrum hole is part of the secret to making key operation snappy. Too far away, and the action is sludgy. Too close and the key won’t return at all, it stays depressed. Getting it just right is tricky. Best to start with the spring being a smidge too long. You can always cut or file or sand some off. You can’t put it back on! Once you get it right, note the distance that worked best.

Also good to remember to grease the tip of the spring or you might take more off than needed.

Yes. The shape of the G# key touch essentially copies the Long F touch. Being asymmetric, it doesn’t impede L3 covering hole 3 as much as the symmetric key touch can. And flaring out like the Long F touch provides more surety for L3 pressing G#.

Yes, I think so. And the key would act more as an extension of the finger.

It probably allows the key to be a little longer too, which would help! The G# is the shortest key on the flute, and that makes springing harder.

I tried to come up with a method for cutting diagonal blocks and slots but gave up. I mill my blocks and key slots, and it would require finding a way to hold the piece at the required diagonal angle on the mill. Whereas all the other key slots I can do easily between centres - the slots are either along (most of the keys) or across (short F).

I gave it up as “too hard”. And went on to come up with the McG# approach.

Maybe it’s worth reconsidering with 3D printing?

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A double-spring structure used on a Grinter to help reduce the abrasion. for your reference

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Well, Chip, there’s your third option with how to deal with the spring tip pressure.

  1. On bare wood or PVC. Digs holes.

  2. On metal slips.

  3. Use double springs.

I have a number of old flutes that use double springs, but they don’t seem any snappier than those using option 2. When I investigated, I found that the typically brass upper spring had overwhelmed the blued-steel lower springs and pressed it back to the wood.

One assumes they weren’t made like that, so it raises the question how has this eventuated. My guess is this.

Brass is a bit soft to make good springs, so it’s typically hammered on an anvil to “work-harden” it. So let’s imagine Mr Rose doing that and subsequently fashioning it into the sort of spring we see riveted to Andy’s Grinter key.

But then a lot of time goes by, and the brass work-hardens further, especially as each time the key is pressed it flexes the spring.

Meanwhile, the blued-steel springs we see them using back then for the lower spring don’t work-harden any further and are simply likely to get weaker, or even rust away a bit. Or in some cases I’ve seen, rust away completely!

So, that’s my guess as to why you rarely see the lower spring on period flutes sticking up much! They’ve been turned into option 2!

I often wonder how long that process takes, and if it’s inevitable. We need to watch the keys of modern makers for any sign of overwhelming.

It’s why I went for my phosphor bronze bearing on stainless steel slips approach.

Andy, Michael Grinter’s upper springs look like brass, but what do you think the lower springs are? Doesn’t look like steel in the image, but that could be deceiving. I wondered if they could be Beryllium Copper? It’s a good spring material like Phosphor Bronze, and would have the advantage of not rusting.

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Ah, and I came across the period reference to greasing the tips of springs…..

“The springs

Sometimes after a fall, or from the effect of pressure, or some other accident, THE SPRINGS will get so weakened that the keys will not stop closely; this will be best remedied by applying to the nearest watchmaker, who, after taking off the key, will easily strengthen the spring by very slightly increasing its bend. If the end of the spring is touched with a little tallow-grease, before replacing the key, it will work more freely.

It is scarcely necessary to repeat, that the author only intends the foregoing remarks for the government of those who, from some cause or other, cannot avail themselves of the services of a proper workman:- to such, he has no doubt the directions here given will prove extremely useful.”

From https://www.mcgee-flutes.com/Lindsay.htm

Lindsay goes on to give Double Springing his endorsement…

“The springs of Keys should on no account be too strong; and from the readiness with which the improved DOUBLE SPRINGS are found to act, they are, though a little expensive, entitled to a most decided preference.”

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And here’s a look at an earlier example of Double Springing, this one the Bb key on Rudall Rose No 519, probably circa 1826.

You can see a steel spring, screwed to the body of the flute. To the left, the same cork dot silencer as you saw on Andy’s Grinter image. (I use the same.) The tone hole to the right reminds us that “Purse Pads” were used in that era, rather than the card-backed pads we are familiar with. Purse Pads is a modern name, coined by Phillip Bate. The period name was “Elastic Balls”!

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I took the photo when maintaining the flute for a friend, so I can’t check the material now.

It’s hard to distinguish‌ from the color as BeCu could be goldish or reddish, depending on the alloy composition. but yes it’s a perfect material for spring.

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Here are the springs I’m using

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Oh, and one final note before I let other people get a word in edgeways….

The old flutes usually used brass springs, but I went for Phosphor Bronze. Why?

It takes us back to the question of work hardening. That brass tends to continue to harden with time and use.

The problem with that is sometimes the brass springs get so hard, they snap. And that’s a real pain. Typically the springs are riveted to the back of the key touch. And then a cork silencer glued over that to prevent the key clacking. And a pad fitted and carefully adjusted to seal properly.

And so, the repairer has to remove the old spring and rivet, and solder in a new rivet. Which requires removing pad and silencer.

Soldering in the new rivet messes with the work hardening of the key body, and oxidises the key metal.

Then replace the spring and get it working nicely again, with a nice snappy action. Then clean up the oxides and repolish the key. Then replace silencer and repad the key, getting it sealing perfectly again. So what might seem like a simple job is actually quite involved.

So I thought better to make sure by using a well regarded spring material like Phosphor Bronze and hope that gets round the problem! So far so good!

And perhaps telling that you don’t see commercial springs offered in brass.

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Ah, and if I read the description correctly, we’re talking stainless steel? That would solve the rust issue. And bendable to suit our needs, which spring steel often isn’t. And presumably you find them springy enough?

I couldn’t see any reference to thickness. Ebay doesn’t me make shopping easy!