Thanks for the quick reply Dave, tis much appreciated.
dcopley wrote:
Because if the ring is fitted the way you describe, it usually falls off as soon as the flute spends any time in a place drier than where it was made.
But the hoop stress is immediately transferred to the ring. JonC mentions what can happen next when the wood tries to expand when it find itself outside of the oven.
It'd be interesting if you had notes (I actually typed 'logs' but that would be confusing!) of the locales in which the flutes that failed were being played. It be great if there was a central repository of such information, I'm sure Terry et al would find it v.useful in comparing places and methods of manufacture versus locales where failures occured.
dcopley wrote:I don't "bang" the liners into the wood. As you correctly point out, this would introduce a tensile hoop stress in the wood, which is very much to be avoided. I make the tubes so that they can be pushed in with minimal force, and rely on the glue to hold them in. I do it after the rings are attached.
(my bold)
We seem to be congruent on this particular point! In retrospect, "banging them in" was overstated. But it would seem from what Terry and others have said, certainly the old makers would force the liners in, probably with gentle rapping from a wooden mallet or similar. The scoring of the headjoint from the burrs definitely implies that.
"It might be a bit better to tune to one of my fiddle's open strings, like A, rather than asking me for an F#." - Martin Milner
GaryKelly wrote:Thanks for the quick reply Dave, tis much appreciated.
But the hoop stress is immediately transferred to the ring. JonC mentions what can happen next when the wood tries to expand when it find itself outside of the oven.
It'd be interesting if you had notes (I actually typed 'logs' but that would be confusing!) of the locales in which the flutes that failed were being played. It be great if there was a central repository of such information, I'm sure Terry et al would find it v.useful in comparing places and methods of manufacture versus locales where failures occured.
Here is how I picture the stresses. A numerical analysis would be better, but I don't have the means to do it.
When the ring is attached, after drying of the wood, there is close to zero stress in the wood and the metal. Then the wood begins to absorb water and would expand if not constrained by the ring. This sets up hoop stresses (stresses in the circumferential direction). The wood and the metal expand slightly until the average hoop stress is zero. When everything reaches equilibrium, the metal has a tensile hoop stress (in other words it is slightly stretched) and the wood has a compressive hoop stress. These stresses balance each other out. There is also a compressive stress in the radial dirction, so the ring grips the wood. If you dry everything out, the stress states go back to zero. If you baked the wood to zero moisture content, it would shrink even more. Then the stresses would be reversed. The ring would have a compressive hoop stress, the hoop stress in the wood becomes tensile, and the radial stress is also tensile, tending to pull the glue joint apart and allow the ring to detach.
You could also consider temperature changes. Heating would reduce the tensile stress in the metal and the compression in the wood, and cooling would do the opposite.
To answer the second question, all of the head and barrel joint cracks I mentioned occured in central or eastern North America. However, that is also where most of my customers are, so I don't know how significant it is.
Are the rings you discuss forged ?
I have been advised in the past that they need to be, but have not seen a much damage to fancy cast ones. Perhaps because they tend to be heavier.
I've seen very few cracked wooden piccolos; maybe 1 out of 30 over my lifetime.
Any thoughts as to why? Smaller bore? Smaller piece of wood to start with? Different kind of wood? Posts as opposed to blocks meaning more holes drilled thus allowing additional expansion places?
I know, I know, unscientific. But I was wondering what anyone else's experiences were or if anyone had any ideas about the why.
Deja Fu: The sense that somewhere, somehow, you've been kicked in the head exactly like this before.
OK, time for a new reality injection to get our minds around...
Last Sunday I went to our local session. I didn't play that much, on account of having the family with me, including Roisin, our 3 week old, and so having to feed them and get them all home in time for bed. But it was an opportunity to conduct a little experiment which I think you'll find interesting and encouraging.
I should also explain at the start, that the flute I'm playing is essentially unlined, so my previous comments that playing a flute with a lined head will not humidify it do not apply in this case. Further, the flute has a new experimental head, which I've temporarily oiled with baby oil. So regard this experiment as exploratory, I'll repeat it at a later time under more typical and controlled conditions.
Before I started to play, I weighed the flute, a 6-key Rudall 5088 model in blackwood. It weighed 338.5gms, but let's call that 0 so we don't all have to do the maths.
After playing for 30 minutes, it weighed an extra gram, but after mopping out, that reduced to 0.3gms. So I'd mopped out 0.7gms of water.
After an hour, it wieghed 1.3gms more, then .4gms after mopping. By now I'd mopped out 1.6gms (or mL or cc) of water.
I played a little more, but then the food arrived unexpectedly early and I stopped playing. Uncharacteristically, I forgot to mop out again. I ate, we chatted and then we decided to get the kids home. I mopped out and packed up.
By the time I got home, sorted things out, etc, it was now 2 hours 40 mins after the start. I thought, now it will be interesting to see how quickly the flute loses the extra weight. It's in a wooden case, with a shaped polystyrene tray supporting the pieces, and quilt batting inside the lid to keep the pieces in place, both materials covered in velveteen. The cleaning rod and a tube of cork grease live in there too.
Thinking to wrap up the experiment, I weighed the flute again. Now it weighed 0.7gms - it had gained an additional 0.3gms since the second mop out! I thought, hmmm, naughty for not mopping out while I ate - the water inside was probably leaking in as fast as it would if I'd been playing.
I measured it again after about 24 hours from the start. 0.8gms. This pesky flute is still gaining weight a day later!
At 40 hours, dropping back at last to 0.6gms.
At 65 hours, 0.3 gms
At 91 hours, back to 0.1gms heavier than at the very start. Since the resolution of my scales is also 0.1gms, this seemed a good place to stop and report.
So how come the flute continued to gain weight even after I got home? And took about 4 days to lose the moisture gained in an hour of playing?Answer - from the approximately 2gms of moisture on the cleaning stick rag.
So, what did we learn? That an unlined flute certainly gains moisture during playing - I'm sure we could have guessed that. I'll do a lined flute on another occasion, and monitor head and body seperately to see how effective the liner is at containin the moisture.
We learned that leaving the flute wet permits moisture to continue to soak in - you might as well be playing. This reminds us always to mop out after playing, and in situations like summer schools to mop out continually throughout the day.
And we learned that something damp - even as simple as a damp cleaning rag - inside the case will keep your flute humidified. I don't think I'd want to use the cleaning rag as a routine humidifier - then it wouldn't be dry when I wanted to use it to mop out. Also it lies in contact with the case materials and the flute - not ideal. But the Dampit-style humidifiers - a piece of sponge in a capped length of poly tubing with a few holes in the side will no doubt work wonders. Buy one or make one if you live in a dry climate and have a lined flute. Ideally buy a little hygrometer too. A few dollars worth is cheap insurance for a flute worth thousands.
Those are interesting observations. I don't mean to be Mr. Negativepants, but unless you do that several times, and show that the results can be reproduced, it's could just be coincidence. What if you have a weirdly absorbent piece of blackwood? Or a really oily one that's taking up less moisture than most blackwood?
And you mention that the resolution of your scale is 0.1g; do we know how accurate it is? Those results could all be within 0.5g, for example; in which case, there's a slight increase in weight. Is the flute keyed? If so, do the pads absorb water? If the pads aren't hydrophobic, they're probably perfect little sponges.
I don't mean to say that your results are invalid, but they're simply an observation on that single flute under those conditions. It would be important to know, I think, how several flutes would act under the same conditions, with attention paid to keeping track of the ambient conditions (Temp, RH).
A lot of valid scientific results arise from investigations of anecdotes. And, I think that Terry's conclusion regarding the importance of mopping out is, at least intuitively, a good one.
And JUST to end on a negative note . . . heh . . . a maximum weight gain of 0.8g? That's 0.8cc (or ml) of water. You could probably smear a whole CC (ml) of water onto the surface of a flute and not see it, given all the pits and valleys a natural surface has. Think about it. If a flute were a CYLINDER with a diameter of 3 cm, and a length of say 20 cm (little fat flute), it'd have close to 280 square centimeters of surface area. 1 CC of water, spread evenly over that much area, would be less than 0.04 mm thick. Isn't it unlikely that the water was anywhere but the surface?
If you took a piece of blackwood and soaked it in water for a day, how much heavier is it afterwards?
Heh heh, I did say it was exploratory. Actually, probably better for someone else to replicate the experiment. It's more of interest and concern to people with lined heads and barrels.
The scales come with a calibration weight and a two-point autocalibrate routine (which I ran before taking the measurements), so I'd expect the accuracy to be at least as good as the resolution.
I'd expect most of the initial weight gain to be concentrated in the head, where most of the water lives. But the subsequent gain is probably distributed throughout the flute, indeed probably along the sides of the flute, as the tops and bottoms are burrowed into the tray and headlining. That's not a worry, as the moisture will diffuse throughout the wood, and as we've seen from my and Dave's results, suprisingly quickly.
Not too worried about temp and ambient RH as inside the case their effects will be substantially reduced, and during playing the breath swamps both.
Soaking a piece of blackwood won't be realistic - it will absorb rapidly through the endgrain, whereas most of the moisture in a flute is only in contact with side grain.
Thanks for posting this information Terry. It lends support to the idea that if you play a flute every day and keep it in a reasonably airtight container, you don't have to worry too much about additional humidification.
I must, however, protest your use of baby oil. There are many more humane alternatives available which don't involve squeezing innocent babies.
I keep my rosewood unlined sweetheart flute in it's case with the damp rag I use to swab out the flute. Because things are so dry here during the winter the rag isn't wet the next day. I consider it a poor man's dampit.
While I don't have a good scale, the flute is still heavier the next day, but I have no idea if it's heavier than when I first put it in the case the night before.
dcopley wrote:Thanks for posting this information Terry. It lends support to the idea that if you play a flute every day and keep it in a reasonably airtight container, you don't have to worry too much about additional humidification.
There is still the issue with unlined heads that the liner prevents direct ingress of moisture from within the bore. But perhaps moisture absorbed by the lower (unlined) parts of the flute, and moisture in the rag would humidify the air in the case enough to humidify the head. So maybe buy the hygrometer first and keep it in the case - it will tell you if you need the dampit!
I must, however, protest your use of baby oil. There are many more humane alternatives available which don't involve squeezing innocent babies.
Dave Copley
Loveland, Ohio
You have to remember I'm getting old, and babies are easy to catch and don't struggle much. My days of harvesting emu oil are done.
Baby oil is essentially a light clear mineral oil (plus some smelly stuff). Commercial bore oils are also usually light mineral oils. I couldn't help wonder if baby oil would work as well. It certainly seems to work OK. I made the head, gave it a quick dose of baby oil, had lunch, came out and played it. Then I gave it another dose of baby oil, and played a few hours for two Tsunami relief events. Since then a gig and the session experiment I mentioned. No pretence at breaking in, no apparent damage.
Tell us something.: You just slip out the back, Jack Make a new plan, Stan You don't need to be coy, Roy Just get yourself free Hop on the bus, Gus You don't need to discuss much Just drop off the key, Lee And get yourself free
"It might be a bit better to tune to one of my fiddle's open strings, like A, rather than asking me for an F#." - Martin Milner
