Sounds like a good plan, Casey. Would you make it flute wall thickness (say 4mm), or rather bottom-of-tenon-trough thickness (say 2mm), which is more the situation here? With maybe thicker shoulders to define the trough (2.5mm?)?
And some combing? (I imagine, if you don’t have the combing, and any shrinkage occurs in the middle of the trough, you might get the effect of the pack sliding into the middle, causing a run-away effect.)
Terry
I’m aware of bindings on bansuris etc, but I don’t actually think that relates all that well to our topic. Firstly, bamboo is a grass, and I don’t know how it works in comparison to wood. Secondly, we don’t have a situation where the binding is in the middle of a long piece of relatively thick wood. Thirdly, if your theory of end-grain absorption applied, wouldn’t we expect to see maximum shrinkage at the tip, or at least the tip end of the thread trough? This shrinkage is a max in the middle of the thread trough.
I think thickness of the material under the thread might be really important. We know that, if you double the width of a piece of wood, it doubles its resistance to bending, but if we double the thickness of the piece of wood, it squares its resistance. So, I’d expect wall thickness (say 4mm) wood to be 4 times less likely to collapse than bottom of thread trough (say 2mm) wood. Whether the combing reduces the strength further, I don’t know, but, as I said to Casey above, it may have an important role in preventing the threads ganging up on the weakest point.
So, I’m attracted to Casey’s plan because it can emulate the known situation. If it doesn’t reveal anything of interest, we might need to cast the net wider!
Terry
I think Rama’s right to look at the thread’s elasticity/ability to retain tension.
The tension in the thread is what’s actually applying force to the tenon. There are no weights or locks, just friction, tie offs and the initial one time tension we add.
There are easily a few ways thread wraps lose tension (which we’ve hashed out a couple times already). I don’t think it’s a great medium for storing energy the way we use it. Nor do I think the thread needs to move much at all to lose most of the tension we put into it.
Terry - Was I correct that you shouldn’t have combined radii forces? Thus in this situation making it an even 700g around the tube. If that’s right it brings the total wrapped pressure down to 20lb assuming we’re using the breaking point of the thread. I’d say it’s easily half that done comfortably by hand.
In any case considering at one point you were thinking it was close to 1.5tons and not arguing with figures over 500lbs … if it’s more like 10 to 20lb, seeing as those numbers are so dramatically different, does that give you pause to rethink your position on thread wraps?
As for bamboo, its is technically a grass as you say but still considered by those who work with it and wood also as a plant “wood”. Although it handles moisture well it is important to protect it from moisture getting in WITH THE GRAIN otherwise its wood will deteriorate and get sculpted subject to the pressure its under.
Just some unprofessional thoughts for what they are worth.
• I can’t handle the pressure!
• This thread goes on for miles.
• I’m getting a pretty good “wrap” out of this thread.
• Whoa this thread is making me dizzy
• “Auntie Em, Auntie Em!”
Thanks folks, I’ll be here all week. Try the buffet.
BTW, this is an image of all ten pages [to date] of this thread mapped to a helix in Cinema 4D. OK, so I was bored.
Cheers,
Kirk
That is SO COOL!!! How did you do that, and more importantly, what kind of compressive force is applied to the center of the spiral by the ten-page wrap? 
I used a program called Paparazzi to capture the images. It will take a snapshot of an entire Web page no matter how long it scrolls. I had to piece the 10 images together in Photoshop and make one really long image out of it and then I used a 3D program called Cinema 4D, created a helix shape and mapped the image to it. Sounds complicated maybe but like Harry Blackstone Jr. said, “all magic tricks are easy once you know the secret.”
Kirk
What I cannot wrap my own head around is how anyone could read the physics report as provided by Terry and still maintain that it’s not possible to apply thread in such a way as to exert a crushing force. Everyone read this again (minus Terry’s asides this time to shorten it up):
so ya want to flaunt yer lack of imagination 
I’ll get around to that experiment later today or tomorrow or the next day. Preoccupied with other matters…
I was curious how strong a tenon was when a point force is applied to it, as opposed to an even force such as applied by thread wrapping compression. So I turned another tenon piece, 3/4" ID, 1.85mm wall thickness, 33mm long. Then weighted it on my scale, pressing against it with a flat piece of steel so that the force was applied in a line. It failed somewhere around 16kg (35 pounds).
The big lesson here is don’t leave your flute assembled, and set it on the couch at a session where someone will sit on it. The tenons and sockets will suffer. I have seen this happen too many times.
Casey
Rob, Terry, what is the correct interpretation of that “700 g per unit-length”? Is the breaking strain expressed thus, or simply as a weight applied to ANY length of the thread? I’m still hiding behind being a physics/maths dunce, and yes, I have looked at the basic formula Terry’s friend set out… but I’m not clear how he gets to 700g per cm… Put another way, if your thread breaks when you hang a 700g weight on it, what is the tension per cm (or any other unit of length? Surely it is the same regardless of the length?
If my befuddled noddle is getting anywhere with this, if the tension in one full circumference-length of thread (2piR) applied T/R inwards radial force, the figure derived from that calculation would be the total radial pressure applied by that circuit of thread around the circumference, not the point pressure? So Terry’s 4.4k would be distributed evenly around one thread-line. If I’m right and we stick to the Professor’s 1cm radius and a tension of 700g, any given 1/10th of a mm of wood under the thread would be receiving inwards pressure of 44g? (Mathematicians HELP!)
(EDIT: Duh, no. 
Obviously, if the radial pressure per cm is 700g, then per mm it will be 70g and per 0.1mm it will be 7g??? I got distracted by Terry’s gross figure and divided the wrong thing! Or will it? - This is where I’m confused by the “unit length” bit…)
Even if I’m way off with this, I still don’t think we have a full and accurately applicable model in discussion regarding thread pressure… even if that is the/an agent of tenon bore perturbation.
(I agree with George here that using the thread’s breaking strain is way over the top, BTW, no matter how you apply the tension while winding.)
Another thought on the middle part of lapping-trough angle… The trough is the thinnest part of the wood and thus the most susceptible to any disruptive influences - de-and re-hydration, thread pressure, shrinkage from of-its-nature wood cellular structural changes with aging, etc. The ends of the trough usually have shoulders of slightly thicker wood which will act as supports to the parts of the trough adjacent to them, and the body-end of any tenon is further supported by the still thicker wall of the main part of the joint. Therefore, the central area of the trough is the least re-inforced/weakest. It might just be that in some instances - particular pieces of wood - it just does this “by itself” because of its particular structures and the shape the maker cut it to, maybe “helped” by usage factors like moisture… It also occurs to me that this problem seems to be commonest and most severe in upper-body upper-tenons - the ones with the largest diameter and therefore with reduced cylindrical structural strength - I believe I’m right in thinking that a smaller diameter tube will be stronger (against compression or shrinkage) than a larger one with the same wall-thickness?
jem, please can you remind us roughly how hard we are supposed to pull when wrapping a tenon. I thought it was just supposed to be a wodge of something with a bit more ‘give’ than wood.
Did you folks do about Hook’s Law at school ?
I know, I’m getting duller by the day. Trying to stay “dry” for once.
Rob
Don’t think I’d ever heard of Hook’s Law… not that I remember.
How hard to pull? Well, to some extent that is defined by the breaking strain of your thread! - Less than that, obviously!!! As I whip it on by hand, I pull as hard as is comfortable to the tip of my thumb over which the thread passes, give or take (as mentioned previously) losses of tension when pausing/setting the work aside mid-wind… I have no idea what actual average tension I may achieve in my chosen thread. I certainly don’t achieve a constant, even tension. One reason I might (continue to) argue against use of hard-spun (and thicker) threads is that, per thickness, they take higher tension than a similar thickness loose-spun thread, as well as having a harder, more abrasive surface. Pipers hemp is usually pretty loose-spun and pulls apart (breaking strain!) quite readily. “Button thread” would be at the other extreme.
OK, Hooke
Thanks. I am fairly sure that for the effect of the winding tension to add up the way Rob is concerned about (and for anything ‘per cm’ to matter)) the thread has to be stretching elastically, which natural fibre threads don’t, much. I suspect pulling hard on a ‘soft’ natural fibre thread is mainly making it a bit more like a ‘harder’ thread.
You left in the bit where Terry assumes you add the radii together, the brackets are his voice. That’s going to raise the force.
I don’t remember one person in this thread ever saying it’s impossible for a thread wrap to deform a tenon. You are currently arguing a position no disagrees with on the one hand and somehow conflating that to understanding the physics involved on the other. To be clear I’m not arguing that it’s impossible for a thread wrap to warp a tenon. For example you could use a much stronger/thicker thread and something to aid in keeping the tension on the thread (like wooden handles) as you wrap, that would significantly raise the force applied.
My position is that with the materials normally used, the manner in which they’re normally applied and the medium’s ability hold energy the wrap won’t be pushing down with enough force to warp a tenon.
What exactly is your position? I ask because you’ve said a couple of times that a properly wrapped tenon won’t hurt a flute, how do you define ‘properly’ in this situation?
To answer your question at the top, there hasn’t been much arguing over this latest “physics report” I think because it sounds a lot more correct. Before, where you had outrageous figures for the force being applied to a tenon, that’s the stuff I didn’t buy for a second. More than going along with them you were questioning why someone would doubt them. Seems you had as little understanding of the physics involved as the rest of us, took an absurd position (going along with the 1.5 tons of pressure) only now I get the impression you feel you’ve been correct this whole time.
I cannot be responsible for lazy reading. However, if you must have a succinct version, here it is:
When threading a tenon, don’t feck up.
What figures did I present, exactly? Careful reading, slow down, check the names. 'Twarn’t me.
Rob
So far as its possible to compare like with like what happens to a wrapping with age ? What are old wrappings like ?
No lazy reading on my part, you haven’t defined “properly” until the above. Good advice, really helpful and totally adds weight to your argument. Keep’em coming …
I didn’t say you presented figures. You think I’m the lazy reader!
More than going along with those figures you were questioning why I didn’t believe them …