Another strangled flute

[Rob Sharer]

I believe the main problem with cork is poor application, resulting in an ill-fitting joint. Unlike thread, cork has very little tensile strength and so can't be pulled taut around a tenon.




Rob

[Denny]

hah! I've wrapped my head around lots of things that never happened!

But have you wrapped your head with thread?

yes, of course!

only in the summer months though.

[Nanohedron]

Fascinating discussion, and what I've gotten out of it may be condensed to "Squish Happens". Thanks for the topic, and I'll mind my tenons all the better now.

[jemtheflute]

Of course, Boehm had the most elegant system and used neither.

He made wooden flutes too, you know, and I believe (haven't gone to check) used the "French slide" design which has the metal male head-liner sliding into the metal upper body socket/tenon, the outside of which is corked and slides into the metal lined socket in the head.....

[I.D.10-t]

I had a feeling you would call me on that. Which of the two are still around?

[Jon C.]

Can't get one past Jem!

[jemtheflute]

I had a feeling you would call me on that. Which of the two are still around?

Quite a few wooden ones extant - go check the DCM! (Here's a link preset for a search on "Boehm":http://memory.loc.gov/cgi-bin/query/d?d ... mmem_st1B:.)

[benhall.1]

As with most things, the following is true:

Just because you can't wrap your head around it, doesn't mean it isn't happening.

I'm inclined to believe these flute-making fellows. In addition to our two esteemed contributors here, I've also had conversations about this very thing with Patrick Olwell, Chris Wilkes, and other makers and restorers of no little repute. To a man, they all acknowledged tenon warpage as a possibility when using thread; each had a preferred type of thread and application technique to avoid damage.

How many such reliable reports from the field would be enough to convince the skeptics?


Rob

Apologies for going back up-thread for this, but ...

Not disputing that they would both say that poorly applied thread may cause damage, but Chris at least still prefers thread to cork (at least on some days ). What does Patrick think?

[Rob Sharer]

Apologies for going back up-thread for this, but ...

Not disputing that they would both say that poorly applied thread may cause damage, but Chris at least still prefers thread to cork (at least on some days ). What does Patrick think?

Paddy uses cork on his own flutes for the most part, but I've seen him thread a few tenons on older flutes, either to match what was there or for some other nefarious purpose. I also know a few folks whose Olwells came with thread, by request.


Rob

[benhall.1]

Thanks Rob. That's pretty much as I would have guessed.

[m31]

It seems ridiculous to me to think a thread wrapped tenon is really a coiled up bundle of crushing force. Especially when you're not putting crushing force into wrapping it in the first place!

Tightly re-wrapping a dried out flute and then abruptly rehydrating it will significantly increase hoop stress (that's what rings are for or the threading on bamboo flutes).

Just because you can't wrap your head around it, doesn't mean it isn't happening.

Yes but it is fallacious to hastily accept an unproven model by virtue of its plausibility. I must admit though, I am partial to Terry's explanation.

[George]

The thread is 0.1mm thick, and can support a load of 700gms before snapping. The thread trough is 15mm long, and about 1.3 deep on average, with respect to the inside of the socket. So it would accommodate at least 150 x 13 threads without packing them in, which could support a total weight of 1.365 tonnes.

700gms is just over a 1.5lbs ... At no point can you use more pressure than that without breakage. Also, no one wraps a tenon anywhere near the strings breaking point, you'd end up snapping it on accident. My guess is it'd be about half that pressure going on before it begins to lose tension settling.

If you still think pressure multiplies with each wrap, grab a pencil, wrap thread around one spot (with constant light pressure, say maybe 0.75 of a pound) until the wood snaps from the crushing force created. It won't by the way.

So the argument that maybe half a pound of pressure distributed evenly over a tenon (honestly I doubt it's even that much) is going to cause compression still sounds silly to me.

What about tenon rings, when fit snugly must apply much more than half a pound of pressure, do they cause warpage and compression? I always thought they were there for protection and to add support and strength. Isn't that the same concept as one of the arguments put forward for thread wrapping?

What about the metal band at the end of tenons on Hamilton flutes, they certainly don't move, anyone heard of problems with them?

Again, the barrel must put way more pressure on the tenon, corked or threaded.

As with most things, the following is true:

Just because you can't wrap your head around it, doesn't mean it isn't happening.

First I 'have a lack of understanding' about strings stretching even though we were saying the same thing. Now it's not that I don't buy your point, it's that I 'can't wrap my head around it' ... I'm not trying to be rude, but do you honestly feel I'm incapable of understanding your posts? It would just be easier for me to get that out of the way =)

[Rob Sharer]

Just because you can't wrap your head around it, doesn't mean it isn't happening.

Yes but it is fallacious to hastily accept an unproven model by virtue of its plausibility.

Fancy talk, for sure. But...who's hasty? And what's unproven?

Terry, Patrick, Chris, Jon....all have taken years to form their conclusions, years spent head-down over the bench, not the keyboard. I for one am prepared to accept expert testimony as very persuasive, especially when it comes from several reliable sources.


Rob

[talasiga]

I am not an instrument maker, nor do I have a lot of experience with threaded tenons, but I think we are looking at this the wrong way. I am a woodworker and I think the force that we would be dealing with is the force of the wood expanding and contracting, not the thread tightening. I have seen images of wooden furniture that was improperly constructed literally self destruct from wood movement.

The example of wrapping the finger with thread might be actually quite a good example. When you wrap the thread around your finger it seems to tighten, but what is actually happening is that the thread acts as a tourniquet and then your finger starts to swell. If you had one wrap of thread, it would be able to stretch and this tourniquet effect would be minimalized, but with many wraps of thread, there is no give at all, you might as well have a pipe clamp on there, the finger continues to swell and if left alone, the tip of the finger would die.

I think this is similar to what would happen with a flute tenon. When the tenon gets wet, it will swell. Cork can stretch along with it and not cause any deformation. But the thread would not stretch and the wood would deform around it, crushing some wood fibers and not others. When the wood dried, it would not necessarily go back to its exact same shape and size. This is what happens with wood furniture and I believe this is what you might be seeing in the tenons over many cycles of expansion and contraction.

I wonder if how one starts wrapping the thread might be the reason some have problems and other not. If you started wrapping kind of loosely, there would be more "give" next to the wood and less pressure when the wood expands, but if you wrap tightly, there would be less ability of the thread to "absorb" the expansion and you would get more wood cell deformation and damage to the tenon.

There are certainly lots of great flutes out there with threaded tenons that don't have damage. Maybe those makers/repairers/users have learned to wrap the thread in a way that does less damage.

Interesting contribution I thought.

[Maihcol]

I believe the main problem with cork is poor application, resulting in an ill-fitting joint...Rob

Yes, this is the problem with thread too.

The topic of thread wrapping joints comes up regularly on the Earlyflute list, since thread is more commonly used with those flutes. From following that list over the years, I'd say that the consensus is that it is the way that the thread is wrapped on the tenon is what's important - and not so much the thickness of the thread or what type of thread it is. For example, Rod Cameron has commented on the number of times he has come across flutes - including historical flutes in museums - with the tenon on the top joint deformed by badly wrapped thread and the narrow A and B octaves that this causes.

He says he uses a thin silk thread about the same as the 0.1mm thickness Terry mentions in the case above but points out that it shouldn't be wrapped on tightly, in neat parallel rows which will make for an overall hardness in the lapping. Others recommend similarly thin cotton or polyester sewing thread - or thicker linen or hemp - but with the final wraps done with a thin thread for fine fitting of tenon to socket.

I use a thin polyester sewing thread on my flutes with a shallow lapping trough - since they're delrin - and I use the lathe to wrap it fairly tightly but of course that mustn't be done with wood.

Garry