Another strangled flute

[benhall.1]

Yes, I read that comment all right, Denny. But that's a theoretical comment about what bore narrowing in that area tends to do. It doesn't mention how it had - or might have - affected that particular flute. I'd also be interested in the actual effects on other flutes as well. Should I read the previous thread? Does Terry mention there the effect that this bore narrowing had on that flute?

[Denny]

can if ya want! viewtopic.php?f=2&t=58167
Weedie sez its got tuning issues....but now what they are.
Terry comes in, 'bout mid page after he's gotten the stick, with the A & B octaves!

I've copied the OP to here and changed the code around the pictures so that they are inline again.

G'day everyone,
I thought y'all might like to see the results of my work with the old cracked Flute.It is,for the time being,finished...maybe later on I'll make the missing rings,but for the moment,the 'fishing rod style' of binding on the top and bottom parts will suffice....I'm not going to bring back the missing keys.
It has a very mellow tone and the bottom D is quite nice...It also has some tuning problems but I've been in touch with Terry McGee and he will take over things for this last stage of the restoration...he reckons that a fair bit can be done to improve the tuning of the old dear...
I've had the BEST time restoring this piece of history...Hope you like the photos.....adios for now...........weedie....
P.S. As regards my thread "Persistence and the Boinking 'h',the little beggar can now be seen .. July 26 t 'h'....

before



after



Assembled 1



Assembled 2

[benhall.1]

Thanks, Denny. I get it now. Boy, does that flute look strangled! I'm off to read the rest of the old thread, in hopes of a happy ending ...

[benhall.1]

I've read it. So glad it had a happy ending. That was a great thread.

Boxwood is weird, isn't it? Chris Wilkes told me about a boxwood flute he was working on - deformed tenon, but not in the same way. It had a tenon that had gone really oval in shape. After scratching his head for some weeks, he ended up soaking the tenon in water for 5 days solid and then leaving it to dry. Miraculously, it sprang back into round.

[Casey Burns]

One thing to remember is that this is a phenomenon that has been observed in old flutes. We are maybe talking about something on the scale of decades or centuries. Thus the current generation of flute players with thread wrapped flutes probably do not need to worry too much about this (I've been getting a few emails from a few clients about this....).

My primary reason for using thread stems from the simple observation that when cork is applied to the flutes I make (despite my recommendations not to and stern warning that this voids the warranty), the sockets usually suffer a crack. Its perhaps because the cork is fit too tightly.

In terms of numbers I did a few experiments that might give an idea of the compression force applied when thread wrapping a tenon. I compared this with the wet and dry compressibility of boxwood.

One was to measure the compressive force directly, when wrapping a tenon. Cork actually works well for this. I fashioned a piece of 1/16" thick cork 1/4" wide and 1/2" long, and wrapped over this using my regular thread wrapping technique and amount of thread. I then removed the thread and measured the thickness of the cork. It had compressed .16mm. I fashioned another piece of cork of the same size and placed it on an electronic food scale, and compressed it with a piece of steel, measuring the amount of force required to compressed it to the same degree as the one that had been thread wrapped over (.16mm). The scale measured 10kg.

Multiplying that by 8 gives the amount of compressive force per square inch, which is 80kg or 176 psi, which is far below the figure that Terry calculated. On my head joint tenons, there is probably about 3.3 square inches, so the total compressive force would be 580 pounds.

I decided to measure how much boxwood would compress if a measurable force was applied to it, using my 3 ton arbor press. I fashioned a 1" X 1" X 2mm thick piece of boxwood, measured its thickness and set my calipers at "0" so I would only be measuring the deviation. I then set it between 2 thick steel plates on the arbor press, and pressed down at full force (3 tons on 1 square inch - thus 6000 psi) and held it there for a minute or two until my arms were tired. I then immediately measured it and found it had been compressed only .02mm at the most. 6000 psi is 34 times the 176 psi that I measured on the tenon, yet it only deformed the wood .02mm.

I then soaked another similar piece of wood in water and repeated the same experiment. The wood was considerably more compressible, deforming by .05mm.

I suspect that its the moisture deformability combined with the inward pressure of both wrappings (either cork or thread) and socket that compresses the tenon over a long period of time. A solution to this would be to seal the socket so that moisture doesn't get into the wood.

It would be interesting to see how much the cork in the corked tenons compresses with use, and compare it with my measurement above (176psi) to determine if there is a significant difference in compression on the tenon, as a result of the thread being wrapped. Does cork get compressed thinner with use?

Casey

[talasiga]

......I then soaked another similar piece of wood in water and repeated the same experiment. The wood was considerably more compressible, deforming by .05mm.

I suspect that its the moisture deformability combined with the inward pressure of both wrappings (either cork or thread) and socket that compresses the tenon over a long period of time. A solution to this would be to seal the socket so that moisture doesn't get into the wood.
.......

yes, these points are in league with my pre naptial guess in the preceding page

[weedie]

Regarding my old Flute ...
Yes,this is truly a story with a happy ending ..
It has a beautiful,sweet tone and the tuning is just fine ..Terry did a great job on my Flute and from what I can gather,he enjoyed the process..
I've been playing it a bit lately...with my friend playing her Harp..The combination of Flute and Harp is a nice one and there's something especially nice about playing an instrument nearly 150 years old..
Thanks again Terry

[Terry McGee]

One thing to remember is that this is a phenomenon that has been observed in old flutes. We are maybe talking about something on the scale of decades or centuries. Thus the current generation of flute players with thread wrapped flutes probably do not need to worry too much about this (I've been getting a few emails from a few clients about this....).

Indeed, we just don't know at this stage. It's possible that these flutes were strangled either over a very long time, or over a short time some time in the past, and the current thread simply wrapped around the neck of the dessicated corpse. We need to be on the lookout for modern strangulations.

My primary reason for using thread stems from the simple observation that when cork is applied to the flutes I make (despite my recommendations not to and stern warning that this voids the warranty), the sockets usually suffer a crack. Its perhaps because the cork is fit too tightly.

I can't think of another reason.

In terms of numbers I did a few experiments that might give an idea of the compression force applied when thread wrapping a tenon. I compared this with the wet and dry compressibility of boxwood.

One was to measure the compressive force directly, when wrapping a tenon. Cork actually works well for this. I fashioned a piece of 1/16" thick cork 1/4" wide and 1/2" long, and wrapped over this using my regular thread wrapping technique and amount of thread. I then removed the thread and measured the thickness of the cork. It had compressed .16mm. I fashioned another piece of cork of the same size and placed it on an electronic food scale, and compressed it with a piece of steel, measuring the amount of force required to compressed it to the same degree as the one that had been thread wrapped over (.16mm). The scale measured 10kg.

Multiplying that by 8 gives the amount of compressive force per square inch, which is 80kg or 176 psi, which is far below the figure that Terry calculated. On my head joint tenons, there is probably about 3.3 square inches, so the total compressive force would be 580 pounds.

Hmmm, I know that is a lot less than my "theoretical maximum" (thread at breaking strain) calculation, but it still seems a lot. 3.2 standard American males standing on your tenon. Are you sure your tenon amounts to 3.3 sq ins - I'd have thought they'd be less than 1. And that 1 standard American male was plenty.

I decided to measure how much boxwood would compress if a measurable force was applied to it, using my 3 ton arbor press. I fashioned a 1" X 1" X 2mm thick piece of boxwood, measured its thickness and set my calipers at "0" so I would only be measuring the deviation. I then set it between 2 thick steel plates on the arbor press, and pressed down at full force (3 tons on 1 square inch - thus 6000 psi) and held it there for a minute or two until my arms were tired. I then immediately measured it and found it had been compressed only .02mm at the most. 6000 psi is 34 times the 176 psi that I measured on the tenon, yet it only deformed the wood .02mm.

I then soaked another similar piece of wood in water and repeated the same experiment. The wood was considerably more compressible, deforming by .05mm.

Now if your arbor press is the same as mine, it is labelled 3 ton, but I don't reckon there's any way you could get it to press that hard. Mine has a handle such that when fully extended, your hand falls about 500mm from the centre of the axle. The axle diameter, into which a pinion is cut, is 60mm diameter. So the mechanical advantage will be 500 divided by the radius (30mm) or 16.7 times. To get 6000 lb force, you would need to apply 360lb.

Secondly, your force was only applied for a minute. With flute tenons we're worried about months and years. We'd really need to set this up for a long-term test.

I suspect that its the moisture deformability combined with the inward pressure of both wrappings (either cork or thread) and socket that compresses the tenon over a long period of time. A solution to this would be to seal the socket so that moisture doesn't get into the wood.

My argument here is that:
a) the socket is not capable of applying much compressive force (as you said in relation to corking your own flutes, the socket wood gives way), and
b) the thread is applying pressure all the time, the cork only when the flute is assembled. That's a 24:1 ratio even for those good folk who practice an hour daily!

It would be interesting to see how much the cork in the corked tenons compresses with use, and compare it with my measurement above (176psi) to determine if there is a significant difference in compression on the tenon, as a result of the thread being wrapped. Does cork get compressed thinner with use?

I really don't know. I've certainly replaced cork on flutes, but whether it's because the cork has compressed, or been worn away, of the wood has changed diameter, or what, I can't be sure. I'd have guessed that it compresses with time, but then you get old flutes where the tenons are scarily tight you have to sand some cork off before you'd dare assemble them. I frankly don't know what's going on there!

It probably does warrant a long-term test. How would this go? We make two test tenons, using the same dimensions as normal, excepting that the ID is a cylinder whose diameter is whatever the diameter at the centre of the thread trough is normally. By using a cylinder, it will be easier to detect and measure any compression.

One we mount between centres on the lathe, and lap at high tension. The other we lap by whatever process you normally use. Both are lapped until they fit a standard head socket nicely. We record and graph the minimum ID of each every week until they stabilise.

Or we could even do the artificial aging thing - heat the tenons or even boil or steam them to simulate the passage of time. From memory, 105°C for three days is supposed to simulate 25 years. Hmmm, tricky though, dry heat would shrink the wood and take the pressure off, and steam or boiling would swell the wood, exaggerating the effect. Might just have to let time take its time.

Terry

[Maihcol]

Terry, a couple of thoughts. Would the makers who offer a re-reaming service for their thread-lapped wooden flutes - some will do it years after the flute has been made - at some point in time, would those makers not tend to notice a suspiciously thicker shaving frequently coming off the bore at the the tenons, particluarly the top tenon, along with the expected tuning change that causes?

I think it's easy for people to make the mistake of approaching the thread lapping on a flute as though it were a "binding" because it has the same general appearance and bindings are far more common - using that traditional binding technique to hold something firmly in place - Weedie mentioned fishing rods in the other thread about your restoration of his flute. With an old flute which has had many owners, it might only take one owner to go binding - effectively wrapping and pulling the thread very tight, even if all the other owners do it properly.

What you're saying is that there may not be a practical way of doing it properly, without causing constriction of the tenons of a large number of thread-lapped flutes .

I'm guessing you haven't posted about this yet on the Earlyflute list where there is a lot more thread users, makers as well as players, to avoid having to attend to two busy threads on different forums but another thought is that Rod C. has had his electronic bore measurement device running for a long time now - a couple of decades or more I believe, checking bores and though he has commented on coming across a number of flutes with constricted top tenons due to bad wrapping, I haven't seen him mention a chronic problem due to the use of thread itself. Not that you haven't thought of that or anything of course but it seems that makers would have to be unconsciously missing the problem.

Garry

[George]

There is something fundamentally wrong with the models you all are coming up with producing these figures. There's no way a thread wrap is putting 580lbs of pressure on a tenon, let alone nearly 3,000lbs ...

You said yourself the thread snaps at 1.5lbs, if the tension increases with each turn (pushing near 1.5lbs a turn) you'd never get past the first. If you're saying stacking thread with that same pressure on top of each other multiplies it, take 1 strand of thread hold it taut and push it against your leg, then take 10 and hold them taut and push down again. Same dang pressure against your leg isn't it?

Thread wraps that've lost their grip and spin on a tenon (putting out exactly 0lbs of pressure) can look exactly like a wrap that is still fixed. Point being it might look like it's tension filled but really it's not.

[Rob Sharer]

There is something fundamentally wrong with the models you all are coming up with producing these figures. There's no way a thread wrap is putting 580lbs of pressure on a tenon, let alone nearly 3,000lbs ...

And here it is again. What is wrong? Where is the backup for this statement, other than incredulity? As I said before, I think there's a fundamental misunderstanding of the physics here.

Remember my example of the cracked tenon? I know good and well that you can tension-wrap thread to exert enough force to close a cracked tenon (whether you should or not is a different question). I'm sure that's a measurable amount of force, and more than a measly 1.5 lbs. Where is that force coming from, if not the thread?

As for backing up my own statements, I have posed this scenario to a friend of mine who holds a PhD in physics, and is a piper to boot. I have high hopes fro a cojent explanation of what's going on here.


Rob

[david_h]

Put a cork in a lathe and wind a few dozen turns on thread on with a 0.5lb weight hanging on it to give a constant pull. Put a cork in a lathe and wind the same number of turns of sewing elastic onto it with a 0.5lb weight hanging on it. Will the cork deform by the same amount in both cases ? After all, the tension is the same.

You could stack a load of lengths of timber on a cart and lash them down with natural fibre rope or you could use shock cord. Would you have to pull by the same amount to get a secure load ?

I doubt the thread is storing much tension, because it is not very elastic All that tension is forming a compact binding on something that is also not very elastic. I suspect that the tension needed for the bagpipe stock mentioned above is make an initial compression of all the materials, and because there is little stored tension if it ends up lose, because everything was not squeezed down enough, it has to be re-done.

[crossing]

[Rob Sharer]

Put a cork in a lathe and wind a few dozen turns on thread on with a 0.5lb weight hanging on it to give a constant pull. Put a cork in a lathe and wind the same number of turns of sewing elastic onto it with a 0.5lb weight hanging on it. Will the cork deform by the same amount in both cases ? After all, the tension is the same.

What about elasticity? Thread and cork are not equal in this regard, and I believe it plays a role.

I'm not convinced that this is a valid scenario in the first place, but meanwhile I bet we could actually perform this test.

LIGHTBULB! I will be having a tune or two with a Lab Manager from the Materials Science Department at NCSU. I will ask him if we can perform this or some other telling experiment, plus pick his brain about the concepts involved.


Rob

[I.D.10-t]

I would be interested on how different thread materials react and how moisture changes this. Cotton shrinks when what right?

[david_h]

... I'm not convinced that this is a valid scenario in the first place, but meanwhile I bet we could actually perform this test....

Yes, it wasn't meant to be directly equivalent, its an experiment to check out some of the factors involved rather than just throwing brains at the main issue. Same as when I asked about wetting and drying in the too long post above.

If the inner diameter of the tenon has reduced then the circumference has reduced, so the wood has compressed (or shrunk) along the circumference, if due to stress (rather than shrinking) that would be stress around the ring of wood - a hoop stress. If the tenon is thinner at the 'waist' then it must also have compressed (or shrunk) radially; that would suggest a stress in the other direction. The two would be related.