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PostPosted: Mon Oct 21, 2019 6:04 pm 
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There is also the issue of longer pieces requiring use of a lathe with a longer bed, and
difficulties of controlling chatter while turning long, unsupported sections, hence
requiring special mandrels, steady rests etc.

Working with smaller pieces has many benefits for the maker, but I think the split body
flutes (with separate left and right hand components) may have originally come in with
the idea of corps de rechange (interchangeable body sections) that allowed baroque flutes
to be played more easily at multiple different pitches. The idea seemed to catch on after
that and persist even after the invention of the tuning slide.


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PostPosted: Tue Oct 22, 2019 2:16 am 
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PB+J wrote:
I found that series on your website really fascinating Terry, thank you.

It's very non traditional, but delrin flutes use rubber (synthetic rubber) o-rings. I suppose an 0-ring channel would be too deep?

What about in place of cork, a band of silicone? It's virtually indestructible and has a lot of elasticity.

I have a plastic Boehm flute, a Nuvo. It's not a great flute--the keys are kind of slow--but it has a lot of clever features including o-rings at the joints and silicone key pads, which it seems to me would seal well and probably never wear out


I remember back in the nineties seeing a wooden flute with three thin rubber o-rings set into grooves in the top tenon. Seemed like a good idea at the time, but I soon heard no. If you don't keep the rings and the socket well greased, you can inadvertently roll an o-ring out of its groove and have it jam in the much thinner space between socket and tenon, whereupon it puts great pressure on both, and is really hard to get apart.

It does seem strange in this day and age that we depend on the bark of the cork tree, but I haven't been able to think of any thing better! I think one of the plusses is that it is weak longitudinally, so it can't exert any significant force (or resist swelling) like the thread pack can. It's also compressive, so it can take up any spare room (within reason!) if say the tenon shrinks or swells. And it glues well, which a poly product might not.

But keep thinking!


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PostPosted: Tue Oct 22, 2019 2:43 am 
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Casey Burns wrote:
Ah! We'll get back into this banned topic again!

Hopefully we can avoid fisticuffs this time! I think last time, it was a very new and bold revelation, one some were not prepared to countenance. This time we have correlation from Claire's study. That's not to say we fully understand all the implications yet.

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Terry - would you do a test in Boxwood with a corked joint, then the same but assembled with the corresponding socket? It would be interesting to see if the socket compresses the tenon similarly to thread wrapping.

So you mean what would happen if a corked joint were to be left plugged together longterm through multiple drying and wetting cycles? Is the cork's compressibility enough to avoid the problem occuring? My guess is that you'd see some compression, but not as much as thread. But it's not really a meaningful test is it, as we tell our customers to pull the flute apart and dry it after playing?

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Another parameter is the thread wrapping itself. I am finding I can get a cork-like feel if the thread is E gauge as opposed to EE. F is really coarse. D is too fine and takes too long to wrap. These are Gudebrod Thread gauges and the threads used were originally for wrapping hand-made fishing poles. I am thinking of making one or two for myself and competing with the J Pod of endangered Orca whales for the salmon that is swimming by currently. Less salmon this year and the whales are out there chasing them every day. I saw a Humpback Whale breaching just a few miles from my workshop last week. Annoying critters - they frequently keep me from my work! I'd rather be watching them which is similar to waiting for water to boil sometimes.

I digress - am in a manic period though a highly focused one. Today I head back to the workshop the first time in a week after last week's mai out of some 40 flutes.

The Gudebrod thread is Nylon, 3 ply. Unlike all the other similar 3 ply threads on the market, this thread is unfused and so it packs flat with a fair bit of cushion. It may be that your thread compresson derives from this differende as I have never witnessed this in my flutes, including ones made from woods softer than Boxwood such as our local Madrona, Pear, Plum, Almond and Olive. I';ve been using Gudebrod thread my entire career.

If you want Terry I can mail you a few spools for these tests. I'd be curious.

At some stage perhaps, Casey. I'm up to my ears in stuff too at the moment, so I'm not in a position to do anything now. But yes, I think there would be threads that make the problem worse, and threads that reduce the effect. And the thickness of the tenon is going to be really significant, so it goes to flute design too.

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I have a client coming by sometime later. She got her flute corked. Was a total disaster. She is going back to thread and having me show her how it is done. When my Apprentice gets here in May I will have her assistance to make a video. Its not rocket science but I have found a few tricks that some may not have thought of.

What was the problem with the corking? Ineptly done or unwisely done?

I've come across a few flutes that I think just are not up to corking. Typically they have very thin tenons and very thinly walled sockets, so there just isn't enough room for a reasonably thick piece of cork. I like to use 0.8mm (1/32") sheet cork. Sadly it's these flutes with very thin walls that are at greatest risk of strangulation!


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PostPosted: Tue Oct 22, 2019 3:12 am 
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paddler wrote:
I hope we can avoid this discussion falling into the polarizing, false dichotomy that "thread is bad, cork is good". I think this study by Claire Soubeyran, and Terry's later studies, present ample evidence that wooden tenons are a weak point in flute design and that when they degrade they can alter the bore shape and the overall performance of the instrument.

I'm not sure that tenons are the problem, as I've seen no evidence that cork-lapped tenons suffer from any problems. Claire seems to have come to a slightly different conclusion, but I haven't had time to read her work thoroughly and consider the implications.

I guess the question is what alternative do we have for tenons if we want the flute to be compact when travelling, and to permit fine adjustment of rotation. Rose (as in Rudall and Rose) patented a flute that appears to have tuning slides embedded at every joint. But imagine the splitting issues this might introduce!

Image


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PostPosted: Tue Oct 22, 2019 5:25 am 
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About now, we might be starting to think, OK, I get it, tightly bound thread wrapped around thin tenons particularly in relatively soft and thin timbers is going to end up with cellular collapse and compressed or even strangled bores. But, just in case we're getting a bit smug, I am aware that that doesn't appear to be the end of it. As I mentioned above, I haven't even had time to consider Claire's work to see if she references the same issue. Later...

Check this set of bore curves, from my "Classical Bores I have known" page.

Image

If you look at the bore traces over the first 30mm from the left, you can see signs of tenon compression in most of them. Nothing new there, just confirmation that this is a commonplace issue. The varying shapes of the compression is interesting....

Coincidentally, most of these flutes are of the "long body" type, so there is no LH/RH tenon-socket joint, except for Rudall & Rose 5501 and Rudall Carte 7174 (navy and aqua traces). Their middle joint occurs at around 210mm. Note that there is evidence of tenon compression at the bottom of the LH section on both. But there is also appearance of bore expansion just below the joint. What?

All of the flutes have a separate foot joint, circa 320mm in from left. Again we now expect to see some tenon compression leading up to that, and we often do. But again, we sometimes see what appears to be bore expansion just into the foot bore.

Now, in the light of my and Claire's work, it's easy to understand the tenon compressions. The thin wood of the tenon gets wet and tries to expand, the tight bands of thread wrapped around it prevent that. Cells are crushed, and when the moisture evaporates, the wood shrinks to a smaller size than it used to be. This loosens the thread wrap, and the diligent owner compounds the problem by rewrapping the thread tighter. History repeats itself, maybe many times.

But what explains the bore expansions just below the sockets these tenons plug into? If the bands of tight thread are busy stopping the tenons expand, they can't be also expanding the insides of the sockets, can they? Or are we seeing some kind of general collapse except in the areas that that these bands of tight thread are?

And what is the role of the (usually) metal rings that support these sockets? If a band of tight thread can cause mayhem, surely a metal band has some powers too?

I don't have answers at this point, only questions. Just alerting you to them, to demonstrate our work here is not yet done....


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PostPosted: Tue Oct 22, 2019 12:01 pm 
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I think the expansion you see in the bore at the boundaries between the body and foot sections is likely due
to back-reaming. A joint provides an opportunity to introduce a cavity in the bore and some makers take
advantage of that to tweak the bore profile. These cavities change the voice of the flute, and sometimes in
a good way.

I have come to this conclusion based on some experience making replicas of flutes with and without such
cavities. In one extreme case I had a flute with a longer socket than tenon at the foot joint. After disparaging
the original maker (privately) I set about making a new foot, with a longer tenon, to fix the problem, only to
find that it really spoiled the flute's voice. I spent a ridiculous amount of time trying to address the problem,
thinking that I had some how messed up in my measurements. After making several new foot sections, and
trying various bore profiles in the foot, I eventually found that when I reintroduced the cavity, by cutting the
tenon shorter than the socket, the flute came back to life and played beautifully. I even made several inserts
to explore the effect of closing this cavity. I eventually concluded that the original maker really did know what
he was doing, and found a clever, hidden solution to a voicing problem. More often than not, I find that the
original flute make really did know what he/she was doing, so you have to be careful not to let your own
arrogance trip you up when trying to separate out the effects of degradation or trying to "fix" tuning anomalies.

I have also wondered if the cavities were the result of wear from tooling, specifically methods of work-holding,
or perhaps wear from years of cleaning out those sections, but they seem to be a bit too large for that
in the flutes where they occur and not present at all in other flutes. Also, they seem to occur repeatedly in
different instances of flutes from the same makers, so I think they are deliberate.

On the issue of why not just use cork and dispense with thread altogether, the problems I have encountered
with cork are mostly to do with the unreliability of the glue, over time. I have had corked flutes from several
different makers, all highly reputable, in which the cork has come unstuck. I'm not entirely sure what causes
the problem, but I suspect either interaction with bore oil and the glue, or perhaps use of a cork grease that
contains something that interacts badly with the glue. This may happen, for example, if someone uses a lip
balm that has oils added as a cork grease. So cork is also vulnerable to misuse by the end user, and a bit more
tricky to fix.

On antique flutes that are corked, the cork is nearly always deteriorated and breaks off in pieces. Since different
flutes all seem to have different clearances between tenon and socket, they all seem to need different thicknesses
of cork and it takes a bit of trial and error, plus a lot of sanding, to get a good fit. Threading ends up being a
simpler solution for dealing with such variability, and ends up being more reliable if done correctly.

If I can find a thread wrapping approach that is no worse than cork with respect to tenon compression, I would
prefer to use it. I have seen evidence that applying the wrong kind of thread the wrong way can cause serious
damage. I have yet to see compelling evidence that the right kind of thread, wrapped the right way, causes any
more damage than cork. Claire's study shows equal deformation from cork and waxed silk. Terry's studies show
an example of a flute with thread wrapped tenons that has survived over 100 years without ill effects.


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