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Terry McGee

Am I Just Being A Sucker?

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Wondering if concertina repairers ever resort to pressure testing the seating of pads?

 

Pad seating is critical in flutes, but it's pretty easy to do a suck test, so most flute repairers just do that. Being somewhat of a fetishist, I use a Magnahelic Flute Leakage meter to refine that test. The Magnahelic is essentially a combination of a small air pressure generator (an aquarium pump in reality), a regulator to reduce the pressure further, and a Magnahelic differential pressure meter, which is what gives the unit its name. The Magnahelic is set up to read 8 with the end of the tube open, and ideally should register 0 when the end of the tube is closed. In a whole flute, it's OK to be as bad as 2, but any worse that that is likely to weaken the response. Obviously each pad individually has to be a lot better than 2 if that is to be the whole flute result.

 

The meter is sensitive enough to detect airflow through the whorls of one's fingerprint - you need to wet your fingers before testing a keyless flute.

 

I tried out the Magnahelic on the pads of the concertina I'm looking at at the moment, and found most pads registered around 4. One was much better at around 2, some worse around 6. One even scored an 8 - when I opened the pad, I could see that the seat impression ran right up to the edge of the pad at one point. Enough flow to startle the Magnahelic, but obviously not enough to make the reed vibrate.

 

Now that's possibly not a problem for a high pressure, low flow instrument like the concertina, although it would spell doom for the high flow, low pressure flute. I haven't tried it out on other concertinas, and wondered if anyone has had experience here? Is it just a point of interest, with no practical import? Or should one get obsessive and use such tools in the search for perfection?

 

Terry

Edited by Terry McGee

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Hi Terry,

 

I'd say there is sense in the usage of such tools with the concertina, as the leakage not affecting the tone will result in a serious loss of air and thus force the player to possibly undeliberate direction changes.

 

As to your checklist, if you would be executing the "hang test" for a first impression of airtightness, you might rule out the bellows' condition in case of a poor result by identifying (and then adjusting) some leaking pads.

 

Best wishes - Wolf

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Indeed, Wolf. Yes, I remember the "hang test" from the days when concertinas were just being rediscovered (intellectually and in real terms) by folkies here in Australia. Some of those concertinas dropped like stones, but were still forced to work for a living! Folkies had biceps in those days.

 

Now, is there universal agreement in how long it should take a concertina to droop a certain distance? Or is this a question we should put on notice to the World Health Organisation, the G20, or perhaps the International Court of Justice?

 

Terry

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Terry,

I have to wonder if "the drop test" is the best indicator of bellow tightness for all concertinas. Case in point, will a tight 45b Jeffries "hung out to dry" drop faster with its weight than a somewhat leaky 20b mahogany Lachenal? (It has always seemed cruel and unusual punishment to me to hang a Jeffries by one end and let the bellows take the full weight of the other! :o)

 

My general test is position the concertina in normal playing position and to draw the bellows out using the air valve and at first gently, then with increasing pressure press them in.

 

(In the way of general information: this scenario it is also a good way of finding bellows leaks using an eye or open mouth close to the bellows as a detection device. The same sort of thing can be done around the ends to get a general idea of where to look for leaky pads.)

 

Its always an impressive trick in the case of showing off a new bellows to a client to stand a fully inflated bellows on end to demonstrate its air tightness. I'm loathe to do it for very long or more than once, for no real reason rather than a feeling that pride goeth before a bellows fall! :(

 

Greg

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Terry,

I have to wonder if "the drop test" is the best indicator of bellow tightness for all concertinas. Case in point, will a tight 45b Jeffries "hung out to dry" drop faster with its weight than a somewhat leaky 20b mahogany Lachenal?

 

That was worrying me too. I guess you could have a formula to compensate for weight, but that's getting away from the idea of a simple check. The other complication I can immediately see is that the droop starts off relatively fast then slows down, following the usual asymptotic curve. So in theory it takes an infinity of time to droop that last millimetre. We normally get around that by measuring "time constants" - the time needed to fall 63.6% of the full value. But again, it's getting complicated. Anyone have a favourite rule-of-thumb they'd like to share?

 

 

(It has always seemed cruel and unusual punishment to me to hang a Jeffries by one end and let the bellows take the full weight of the other! :o)

 

 

I'm not sure that's a real issue. Firstly, only half the concertina is hanging. My Simpson metal-ended anglo weighs 1.4Kg, so half that is 700 gms (1.5lb). That's not a big load. If I hold the instrument closed by one strap and then open a button on the top side, it doesn't sound vastly louder than when I play. Maybe big instruments would present a bigger issue.

 

 

 

 

(In the way of general information: this scenario it is also a good way of finding bellows leaks using an eye or open mouth close to the bellows as a detection device. The same sort of thing can be done around the ends to get a general idea of where to look for leaky pads.)

 

What, you no longer recommend immersing it in the bath and look for bubbles?

 

Terry

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Don't you need to address the different possible kinds and sources of leakage?

  • Space around the reed pan (usually due to shrinkage) or over chamber partitions (usually due to warpage) can still produce internal leakage even if the bellows and pads are "perfectly" tight, but won't be detected by those "external" tests.
  • Both bellows leaks and leaking pads are "external" leaks, but their consequences can be quite different. Bellows leakage should be pretty much the same whether the bellows is being compressed or expanded. But with pads, opening the bellows will tend to suck the pads down tighter against the board, thus reducing leakage, while the pressure from closing the bellows tends to push the pads up away from the board. In the latter case, weak springs can be a significant cause of leakage, which will be missed by the "drop test"

To check for external leaks (pads and bellows), I think simply pressing and pulling on the bellows with varying strength and no buttons depressed would be much more informative.

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I have to wonder if "the drop test" is the best indicator of bellow tightness for all concertinas. Case in point, will a tight 45b Jeffries "hung out to dry" drop faster with its weight than a somewhat leaky 20b mahogany Lachenal? (It has always seemed cruel and unusual punishment to me to hang a Jeffries by one end and let the bellows take the full weight of the other! :o)

 

My general test is position the concertina in normal playing position and to draw the bellows out using the air valve and at first gently, then with increasing pressure press them in.

 

(In the way of general information: this scenario it is also a good way of finding bellows leaks using an eye or open mouth close to the bellows as a detection device. The same sort of thing can be done around the ends to get a general idea of where to look for leaky pads.)

 

I couldn't agree more Greg!

 

Only don't forget the ear in finding leaks too...

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Indeed, Wolf. Yes, I remember the "hang test" from the days when concertinas were just being rediscovered (intellectually and in real terms) by folkies here in Australia. Some of those concertinas dropped like stones, but were still forced to work for a living! Folkies had biceps in those days.

 

Now, is there universal agreement in how long it should take a concertina to droop a certain distance? Or is this a question we should put on notice to the World Health Organisation, the G20, or perhaps the International Court of Justice?

 

Terry

 

I am not getting involved, I had enough trouble in tuning tolerances

 

Dave

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OK I am interested,

 

I do the same as Greg, in gently pressurising the bellows, this gives me an idea of 'creep', ie general air loss, and You can usually hear pads hissing if there is an issue there.

 

then there is the eye ball/ wet mouth to sense/ feel leaks,

 

to track down specific leaks I have my 'light sabre' a tubular inspection light that I can but down the bellows, this reveals a frightening array of corner and gusset leaks. and I use light to establish specific locations & positions of pad pad leaks as well.

 

Finally I have a pad on a tube which I can use to test pad leaks and also spot weak springs,

 

Although, if you pick up a concertina and extend it, then apply pressure and it feels rock solid then you can ignore drop tests etc. It is surprising how vacuums always decay faster than positive pressures.

 

Don't forget the action box long screws on an English often are part of the concertina seal, and missing, sheared or removed screws can present significant leaks

 

Dave

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What's much more important than the pad pressure is, in my experience, the seal around the reedpan, and the seal between the reedpan and the actionboard. The button pressure is tested in my case with the 'kiss test' - after repadding an actionboard I hold the actionboard up to my lips and blow through each hole. Obvious leaks become easily apparent. However, I have long learnt that most apparent leaks coming from the ends are usually nothing to do with the pads (and tightening the pad pressure up is a complete waste of time and makes the instrument unplayable), but rather are related to loose fitting reedpans within endframes, and/or gaps in the seal between the actionboard and the reedpan. Get those sorted and voila!

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to track down specific leaks I have my 'light sabre' a tubular inspection light that I can but down the bellows, this reveals a frightening array of corner and gusset leaks. and I use light to establish specific locations & positions of pad pad leaks as well.

 

Although, if you pick up a concertina and extend it, then apply pressure and it feels rock solid then you can ignore drop tests etc. It is surprising how vacuums always decay faster than positive pressures.

 

Ditto, except I use a reading lamp - but maybe I should ask Darth for the loan of his light sabre, next time I see him... ;)

 

 

Don't forget the action box long screws on an English often are part of the concertina seal, and missing, sheared or removed screws can present significant leaks

 

That can be an issue in some Anglos, and duets too...

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Now, here's an interesting comparison. I ran the Magnahelic tester on the RH action plate of my Simpson anglo. Almost all pads came in between 1 and 2 on the scale, compared to the typical 4 on the poorly repadded Lachenal I've been looking at. Only one of the Simpson pads read a 4, while a number of the Lachenal pads read 6 and even 8. Now this becomes even more interesting when we compare playing weights. The Simpson buttons require somewhere around 60gms on average, while the Lachenal keys require between 100 and 200gms. So, not only does it leak more, but it leaks more with higher spring pressure. Hmmmm.

 

Now, this is all at the very low pressure designed to test flute pads. For realistic concertina measurements, the tester should ideally simulate typical or indeed maximum bellows pressure.

 

Terry

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Now, here's an interesting comparison. I ran the Magnahelic tester on the RH action plate of my Simpson anglo. Almost all pads came in between 1 and 2 on the scale, compared to the typical 4 on the poorly repadded Lachenal I've been looking at. Only one of the Simpson pads read a 4, while a number of the Lachenal pads read 6 and even 8. Now this becomes even more interesting when we compare playing weights. The Simpson buttons require somewhere around 60gms on average, while the Lachenal keys require between 100 and 200gms. So, not only does it leak more, but it leaks more with higher spring pressure. Hmmmm.

 

How old is each instrument, and how recently were the pads in each installed. (I.e., maybe the Lachenal is due for an overhaul?)

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Now, here's an interesting comparison. I ran the Magnahelic tester on the RH action plate of my Simpson anglo. Almost all pads came in between 1 and 2 on the scale, compared to the typical 4 on the poorly repadded Lachenal I've been looking at. Only one of the Simpson pads read a 4, while a number of the Lachenal pads read 6 and even 8. Now this becomes even more interesting when we compare playing weights. The Simpson buttons require somewhere around 60gms on average, while the Lachenal keys require between 100 and 200gms. So, not only does it leak more, but it leaks more with higher spring pressure. Hmmmm.

 

How old is each instrument, and how recently were the pads in each installed. (I.e., maybe the Lachenal is due for an overhaul?)

 

 

The Simpson is 1993. The Lachenal is around the end of the 19th century. It has all new pads and buttons; my understanding is that it has been recently overhauled. Or at least hauled.

 

Terry

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Are the pivots significantly closer to the buttons in the Lachenal?

 

Argghhh! The questions people ask you just after you've put them both all back together!

 

But, yes, good question. And, peering through the fretwork, I'd say yes. Not enough to account for the big difference in leakage, especially when also taking into account the much heavier springing. But definitely a partial answer. I imagine the Death of One Thousand Cuts is probably involved.

 

Terry

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