Effects of Thread Wrapping series:

Your flute



So, having read all this, and having a flute that is thread wrapped, should you worry that strangulation should happen to you?  Unfortunately, although our experience shows that flutes get strangled, and our experiment shows a mechanism by which it can happen, we can't yet predict whether and when it's going to happen to your flute. 

But here's one circumstance that would definitely ring alarm bells.  If you find, from time to time, you have to add thread, but you don't find you ever have to remove any, I'd be worried.  Unfortunately, it's probably a bit late to be worried, as it probably means serial strangulation has already set in.  But the sooner you stop making things worse, the better.

I'd be more worried about the softer and less stable boxwood than the stronger and more stable blackwood.  But having said that, it's only because I have no experience of blackwood compressing, and that's because I have no experience of threaded blackwood flutes.  The blackwood test tenon was moderately encouraging, showing considerably less distortion after the same tribulations.  But it wasn't a whitewash either.

Cocus, from our survey above, is obviously at risk, as is ebony.  The older the flute, the more likely the risk.  The thinner the tenon, the more likely the risk.  The deeper the thread pack, the more likely the risk.

I'd keep up the oiling, as this should slow water intake.  I'd be very thorough about mopping out, as that at least terminates the water uptake period.  I'd definitely unwrap any flute with a tight binding, and look for something softer I could apply more loosely.  And while I had the wrapping off, I'd look to see if the thread trough is uniform in diameter or hourglass shape or in some other way distorted.  Holding a rule against the tenon shoulders and looking at the size of the gap along the trough is a reasonably sensitive test.  if in doubt, I'd measure and graph the bore for the first 50mm (2") or so at each tenon, and look for signs of compression. 

If you don't feel motivated to go that far, at least investigate the top few layers.  If you found more than two or three separate windings were involved on any one tenon, I'd be worried that serial strangulation might be happening.  If that were the case, I'd definitely check out the tenon below using the rule method.

What about blackwood?

The discussion so far has centred on the timbers we find most commonly in old English flutes - boxwood, ebony and cocus.  We haven't looked at blackwood, Dalbergia Melanoxylon.

I'd have to admit that, personally, I'm not too concerned about blackwood.  It wasn't used in 19th century England much, or in the US as far as I can see, except in modern times.  Most of my own made flutes are blackwood, but then, I use cork, so I have nothing to worry about.  It has seemed to me that other makers using blackwood and thread need to conduct their own accelerated aging tests (with realistically-sized tenons) to see how it stands up.

I'd expect blackwood to be less affected that the three timbers we have been following.  It seems stronger to me, more stable, and more water resistant.  Still, Lord Rayleigh's words nag at my soul.... "What we cannot measure, we do not know".  Sigh.  Alright, m'Lord, let's check it out....

I knocked up another tenon, identical to the first, but in blackwood.  I ran it though the same hoops.  The most dramatic changes to the boxwood tenon had been the end bore and the middle bore, which ended up +0.5 and -0.75 respectively.  The blackwood tenon followed the same pattern - end larger, middle smaller - but the results were +0.25 and -0.25mm, less than half that of the boxwood.  Encouraging, but....

Note, though, that it wasn't zero.  Blackwood, for all its merits, wasn't unaffected.  Just affected less than boxwood.  What our experiment doesn't reveal is whether that's because blackwood is stronger, or more water resistant, more stable, or some combination of all three.  If, for example, we went on longer with our humidity cycling, would it catch up to the boxwood, or is this as bad as it is likely to get?  These are the sorts of questions that anyone thinking of using thread wrapping needs to research.

What did rather surprise me was the degree of ovality that set in - about 0.5mm in an 18mm bore - even when the humidity returned to normal.  As if one axis remained strong, and the other buckled under pressure.  Interesting....

A single point check

I mentioned further up how to measure a flute for bore compression.  That's OK for the well-equipped maker, restorer or repairer, but what about the owner without access to T-gauges?  Is there no check they can do? 

Although to really understand what's going on, you need to measure and graph the bore for at least the first 50mm, our survey at the top suggests one pretty easy "single point check".  The typical 150mm (6") vernier callipers can reach about 16mm (5/8") down the bore if you use the internal anvils (the pointy ones).  Larger callipers have longer anvils, but often only the first 16mm or so are chamfered to prevent interference, so they can only read accurately to the same depth.  Fortunately it's enough to take us to the middle of the tenon, where the shrinkage is likely to be mostly felt.  If you haven't any callipers, you probably know someone who has, even if it means a trip to your motor repair shop.  Be gentle in taking the measurement, you don't want to rough up the nice bore on your flute with the sharp pointy ends! 

So the question becomes what would we expect to see at 16mm down the bore.  That's obviously going to depend on the flute type, but we could hazard a few guesses.  A small-bore flute, if we take the Geo Rudall, Willis fecit as an example, should be around 17.75mm.  A small bored Rudall style flute more like 17.9mm.  A larger bored Rudall or Nicholson's Improved say 18.1mm, and a Prattens around 18.3mm.  If you compare your measurement with the flutes on the graph at the top, you should be able to form a good idea of what condition it's in.

Checking the lower tenons on either the LH or RH section is much easier.  Measure just inside the end of the tenon, and compare it with the measurement you get when you insert the callipers to full depth.  The end measurement should be smaller.  If the full depth measurement is similar or smaller, then you have clear evidence of bore compression.

There's one case where that might be misleading though.  If the foot on your flute flares dramatically (eg on a flute with a Short D foot), the back reaming might have been taken past the foot and into the lower end of the RH section.  In which case you might legitimately see a very small reduction in diameter when you insert the callipers fully.  But if it's a large reduction, it's bore compression.

Getting it corked

You might decide, on the evidence so far, that it's time to get your pride and joy corked.  In theory, that's a straightforward operation.  Any woodwind repairer who handles clarinets (and that's probably all of them) is accustomed to replacing cork.  But there are some significant differences between old wooden flutes and clarinets.  Clarinets were made with cork in mind, so the trough depth is ready-to-go.  Clarinets have smaller bores than the top end of flutes, but similar outside diameters, so the wall thickness is much greater, lending much greater strength.  Old wooden flutes were usually designed with thread in mind, so the trough depth could be anywhere.  And if bore compression has set in, it may well be deeper in the middle than at the ends.  Putting cork on tenons made for thread is likely to put too much force on the thin socket walls, unless the tenon and/or socket dimensions are adjusted to accept the cork safely.  That's a job for a wooden flute specialist, although once done, any woodwind repairer should be able to replace worn or damaged cork in future.  An alternative process is to put on the cork, then sand it to fit the socket nicely.

Now here's something sobering to think about too.  Imagine an old flute suffering both general timber shrinkage and bore constriction (probably 90% of the old flutes that haven't cracked already?).  While the dimensions of the socket might be enough to sustain cork under normal circumstances, the stress from shrinkage over the barrel liner might already be close to whatever the wood can stand, and any increase from any other source might be unwelcome and unwise.  I guess the answer there is humidification or relieving the timber around the slide - take the stress off the barrel wood before applying the cork to take the stress off the tenon and bore.

It would be a shame to compound your tenon compression issue with a split socket issue!  So, ask around and find someone specialising in wooden flutes and cork.  Or at least alert your woodwind repairer to the issues and ask them how they intend to deal with it.

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  Created: 23 January 2011; last updated 20 February 2011.