Another strangled flute

[Arch_Angel]

I got a PSI comparison for the Nearly 3000 PSI. The high presure tanks I used in paintball (compressed air) came in 3K and 5K PSI. Not all refil stations could even fill my 5Ks especially when I brought in my larger bottles.

That said, I think you have overworked your figures. Then again you did use MAX applible pressure throughout. I doubt that would ever happen, but maybe the figure is posible if not highly inprobable.

[Nanohedron]

Fair enough, Nano, though I'm sure you'd agree one is going to apply sufficient tension to the thread to form firm lower layers that upper ones won't cut in to and a surface layer that won't drag during joint dis/assembly.

I entirely agree, and anyone's experience - mine included - would prove you right. That is why, as a solution, once the starting layers are just secure enough ("secure" being the word; while not at all loose, I don't go for an especially super-super-tight wrapping there, but just so much as my hands' strength will reasonably allow) and buildup has come to a certain point, I have come to wrap the uppermost thread layers in a somewhat more crisscross orientation, or at least periodically so, so that when I change directions and thus a new layer is applied, being at cross-spiral there is only support from below and no "cracks" to fall through. The mass eventually compacts, so sometimes I have to add until that consistent, serviceable sweet spot is achieved. I dunno; works for me, and no leaks that I can tell.

Again, though, as I've said before, I'm not really concerned with how pretty the look of it is; I want a good functional result, and I've found this one to be reliable.

[jemtheflute]

Before you can really start pulling, you have to practise your ploughing. Lots.

Furrowing my brow at that one - can't use a plough without pulling it... Carts and horses again!

[benhall.1]

Chicken and egg, I would have said.

[Denny]

the plow is pulled by the pushing horse

[jemtheflute]

Chicken and egg, I would have said.

Only if you're cracked. And as I recall, you're a little ender - explains a lot!
Melon souffle, anyone?

[benhall.1]

the plow is pulled by the pushing horse

Couldn't you have used "pony"? So much more alliterative.

[Denny]

brute!

[Terry McGee]

I don't disagree with Terry's conclusion that poorly wrapped thread could damage tenons.

However, there are severe flaws with the logic behind his maths.

Gasp! Surely not!

Firstly, the tension of an individual thread: the maximum pressure it can exert is 1.5 lbs (accepting that that is, in fact, the case). But, unless renewed pressure is put on the thread, for most of the time, it won't be at that much pressure, because the wood will never be in quite the same state as wehn you first put the thread on - if the wood expands, the thread will break, and if the wood contracts, even a tiny amount, there will be no pressure at all.

You can be happy with the breaking strain - I tied some of the thread to a retort stand clamp and a hook at the other end, and added weights until the thread broke.

I think Jem queried whether you could keep up the tension through the wrapping process - the answer is yes of course, if you use a lathe to create the wrap. (Tempting, given the 150 x 13 = 1950 turns, and two more tenons to go). But even if you wrap by hand, pausing every now and then will only release the tension if the thread slips. I agree with Rod Cameron (as reported earlier) - a jumble wrap is going to be safer than a neat wrap. And I agree that, whatever force is put on the wrap, the wood underneath will crush to reduce the effect of the force. The problem here though is that moisture will continue to expand the wood, keeping up the battle.

Secondly, as I understand these things, what matters is not the total pressure along the entire length of the tenon, but the maximum pressure at any given point. So, you can divide Terry's figure by 150 for a start.

In the pressure calculation (Force per unit area), I'd already incorporated the division by 150 - it's part of the area. You can do it the other way, take one thread, multiply by 13 because that's the stack above it, and divide it by the area covered by that one thread. You should get the same result.

Thirdly, Jem's right - the force at which the thread will break is along its length. That does not translate to an equivalent downward force at right-angles to the force applied along the length of the thread.

Where does that force go then? It has to act on something.

Fourthly, I don't buy this vertical bit, whereby each turn of the thread is assume to add the same amount of force at right-angles to the force applied to it. I don't even know how that could be measured. It could be theorietically calculated, I suppose, but only provided you assume that the tenon is completely immoveable and inelastic. If it is in any way elastic, as soon as it is compressed at all, the tension on the lower layers of thread would be reduced to nil, so the maximum force is still whatever the amount of force is applied by one thread, which is, because of Jem's point, significantly less than 1.5lbs.

I think that's the same argument as above. And of course I don't expect that the full 1.5lbs was used or could be maintained. But, as I said, if you only end up with a tenth of it, that's still a terrible amount of force to maintain on a thin hollow cylinder of wood 24/7/52 etc.

Mind you, if you stuff the thing up with so much thread that you have to force the tenon into the socket, the force you are applying at that time (plus whatever happens when the tenon expands due to moisture) may be enough to wreck the joint.

I think that's actually quite negligible compared to what is already in place.

I guess if we don't believe the thread wrap strangled this flute, who did? We're forced to the only other likely explanation - Aliens strangled my flute!

Incidently, I'm working on another repair - a flute by Camp. All three tenons thread wrapped, and all show signs of bore compression (which I'll define as a localised bore diameter minimum roughly coincident with the middle of the thread trough). Not strangulation, yet.

Terry

[Denny]

Aliens strangled my flute!

Frank Zappa song, no?

[talasiga]

.......I guess if we don't believe the thread wrap strangled this flute, who did? ......

My pre naptial guess is that it was the flute owner or player (oop) and these are the strands for my guess:
* as the tenon was threaded rather than corked the oop was less cautious about removing from socket after play, resulting in (after a fair few years of this)
* moisture soaking into timber via the top rim end of the tenon (and more so if the thing was pulled out a tad for tuning down and more moisture collected in the "gully" if you know what I mean), and in this condition
*any of the other factors such as argued earlier may go towards catalysing or exarcerbation.

(the author, talasiga, asserts the right to deny any deliberate pun that may be perceived in this post, which is a serious post in a light, friendly, conciliatory vein)

[jemtheflute]

For the edification of the mystified..... how to get (in a scrunch!) from Melons to Mangels

http://www.youtube.com/watch?v=HhXnVRX-h_o

http://www.youtube.com/watch?v=D8wQ4ONPbrY

http://en.wikipedia.org/wiki/Mangelwurzel

[I.D.10-t]

I think that's actually quite negligible compared to what is already in place.

In that case would you have tennon splitting or expansion?

[benhall.1]

I've only just thought of this, and yet it's the most important question of all and, as far as I remember, hasn't been answered at all in this thread. (Apologies if I've missed it.)

Terry - these 'strangled' flutes - I know you've measured the bore disturbances and I amd not doubting that it might have been poor wrapping that caused it in each case. But, and this is the important bit, in the case of the particular flutes you mention, what effect did this bore compression have on the playing qualities of the instruments?

[Denny]

Some time back Weedie sent me a boxwood flute to fix up - I posted a note about it at the time. The poor thing had been strangled - the top tenon bound so tightly with thread that the wood underneath collapsed, significantly narrowing the bore. Now, that section of bore is at a very critical part of the flute's acoustics - just a little narrowing there produces quite dramatic changes in tuning. There are other parts of the flute where a substantial change will produce little outcome.