Effects of Thread Wrapping series:

Restoration Issues


Restorer, repairer, accessory-after-the-fact, serial strangler?

You're not really happy with your old flute's performance and so send it to someone for attention.  The technician fixes a few obviously leaking cracks, replaces a few desiccated pads, replaces a crumbling stopper, and tightens up the rocking thread wrapping on the tenons.  Yesterday, we might have called this person a restorer, but can we now?  From now on, don't we expect a restorer to be alarmed at finding rocking thread wrapping?  Wouldn't we expect them to do a few quick measurements to ascertain the level of bore compression that might have set in, and to discuss this with the owner, proposing whatever action seems appropriate to firstly reverse the damage, then to avoid it reoccurring.  Isn't that what we mean by restoration - the act of returning an item to its original condition?  With the aim of keeping it there?

Would we be happy for a "repairer" to replace or augment the thread on our loose flute without checking for damage?  What is a repairer, by comparison to a restorer?  A technician who can carry out routine repairs, but without the full understandings, techniques and resources of the restorer?  Wouldn't we hope they would at least alert us that there might be an issue, rather than just paper over the cracks and tell us nothing?

How would we, in future, regard a technician who whips off the old loose wrapping and replaces it with something neater and fuller?  Perhaps, to keep up the strangulation metaphor, an "accessory after the fact" might be the most generous reading we could make.  The technician didn't carry out the original strangulation, but is not alerting authorities and is covering up the evidence.  But it's probably worse than that, isn't it.  By replacing the loosened weakened thread with fresh and tightened new material, hasn't the technician become the next in a line of serial stranglers?

What are the questions?

Now it's easy, of course, sitting here in my ivory tower, pointing the finger at hard-working flute restorers and repairers, and demanding more of them.  (Um, Ivory Tower?  Well, there are a few small chunks of ivory about, mostly attached to the ends of flutes.  And we are upstairs...) 

But it's only fair that I provide some answers as well.  I'll do my best to help us all come to grips with this new issue.  Some of the questions that come to mind are:

  • How do we measure compression?

  • What's a quick check for existence of bore compression

  • What might the original bores have looked like?

  • What are our options for restoring bore compression?

  • What are the effects of bore compression on tuning?

  • What level of shrinkage are we seeing in old flutes?

  • What are the effects of this shrinkage on tuning?

  • What level of bore compression isn't an issue for the flute?

I'll be attempting to answer all these questions and more in this series.  You might have other questions you'd like answered.  Feel free to raise them with me.

Measuring compression

I should mention that measuring compression is not altogether straightforward.  Most people measuring flutes, e.g. when preparing to make copies, use the regular Telescoping or T-gauge, in conjunction with the micrometer.  Set the T-gauge to say 18mm, and see how far down the bore it will go.  Then move on to 17.8mm, repeat etc.  But, as you can see from the graphs, once you pass the constriction, you need to start opening up the gauge again, not just go on to the next place it stops.

Follow the yellow Strangled Boxwood curve in the graph reproduced below.  Once you get down to 16.3mm, it skims along from 10 to 15mm, and then won't stop until somewhere near the middle of the section!  That's a dead giveaway that something is wrong.  Obviously, it won't be so noticeable on flutes with mild compression, but you'll still notice a bigger step than normal.  Follow the brown Camp trace, and note that there's only about a 10mm step across the cavity.  But you can still detect and map that.

So, the golden rule has to be, when you find a step that's noticeably bigger than any other step, it needs full investigation, not glossing over.  Open your T-gauge a step, introduce it on an angle to duck under the low overhang, straighten it up and note how far in it will go and how far back it will come.  Keep increasing the setting until you've mapped the whole chamber.

A quick check for strangling.

This quick check for bore compression need only take a few seconds.  If, of course, it comes up positive, the restorer might feel obliged to go on to map the damage and report to the customer.

Set the T-gauge to the size of the opening at the top tenon.  Nip the clamp up just enough to stop it opening up when removed.  Now push the gauge down the bore.  You should feel resistance as the decreasing taper forces the gauge further closed.  If there is no compression, you will continue to feel that resistance until you run out of handle. 

If there is significant compression, you will suddenly feel no resistance, as the gauge head traverses the chamber formed after the compression.

You can use a similar test for bottom tenons.  Once set to the ID at the bottom of a section, it should be free to insert further.  If you detect resistance before you detect freedom, then there is compression.

(Note that museums don't endorse this way of using T-gauges.  They reason that, if over centuries, many researchers cram many T-gauges down the bores of the same flutes, measurable wear will occur.  In the outside world, a flute will be lucky if it's measured twice in its lifetime, so that concern is unwarranted.  So, in the museum environment, always use the mapping approach detailed further up.)

A note on T-gauges

T-gauges are one of those simple products that cost rather a lot more than you expect.  But it is worth getting good ones - the cheap ones tend to be unreliable in action.  If you have the opportunity to buy them individually, do so - unless you also work on bassoons you won't find much use for the larger sizes.  I only use three (max opening):

  • 13mm - for foot bores and lower end RH sections

  • 20mm - for LH and head bores, and

  • 32.5mm - for sockets

A message to museums?

What implications does our investigation have for those museums with large and significant flute collections, with many of their earlier flutes still sporting thread wrapping?  Aren't they slowly strangling their exhibits?

I suspect in most cases, probably not.  The instruments are probably being held in stable conditions, free from extremes of heat, moisture and dryness.  If the threads have been on there for years, they have probably already done what damage they can, while the flutes were out-and-about.  But, if they have thought for any reason to have flutes rethreaded recently (perhaps because their collection is a "playing" one), they might well want to reconsider their decisions.

Museums where flutes in the collection are not regularly played will probably wish to retain their thread wrapping as a significant part of the artefact.

We've been here before....

I encounter a sudden stab of déjà vu.  Some years back, I proposed publically that wood shrinkage over metal liners was the mechanism that caused the exceedingly common splits in heads and barrels, while unlined sections of flutes went unaffected.  I think that is universally accepted now, but there was outrage at the time, as a look through the archives of the various Internet forums will confirm.  All sorts of bizarre counter-claims were made, e.g. that expansion of the slide due to sudden changes in temperature was to blame.  Since then, other repairers and restorers have taken up my process of removing the slide, fixing the crack, re-reaming the bore and reinstalling the slide, as opposed to the previous bodge of attempting to screw or stitch the crack closed against the irresistible forces of nature.

In a few years time, flute strangulation will be as accepted as liner-induced splitting is today.  Repairers and restorers will be alert for signs of it, and will have adopted, adapted or developed their own techniques for alleviating it.  Not only will we not remember what the fuss was about, we won't even remember the fuss.  Flutes will yield a collective sigh of relief.


I'll look forward to answering more of the questions facing restorers in future editions.


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