Warped Reed Pan

[duckln]

I finally got around to trying out my 20 b, Lachenal Anglo, sn 403xx.

It was losing a lot of air so I took the right end off.

 

Problem

 

The otherwise pristine looking reed pan has a 'warp', concave on

the 'inside'. The 'depression' measures .130", a little more than 1/8 "

over the 4' span..

It is very stiff , I don't think it can be flexed back without cracking it.

 

The action board also has a belly up 'warp' (.0825"). It is not

stiff and easily flexes back to the 'true' plane of the cover.

The action board does however have minor surface cracking along the

grain about 1/2 " in from the air button.

 

I feel sure that this is common low humidity problem. Any one know

a fix?

 

Joe

[Pete Dickey]

I seem to recall reading somewhere that you apply moisture to the concave side of the "warp" and clamp the piece flat while it dries out. However this does risk damaging the hide glues fixing the rest of the parts and may not be the best answer

 

Pete

[duckln]

Thanks.

I had the clamps ready to go, and was thinking of finding a

'damp' area and slowly applying pressure over a weeks time.

Damping one side, I guess is also an added option.

 

But will it stay true?

 

Looking at it closely, I think the 'culprit' is the cavity walls

mortised into pan allowing it to flex or warp in only one direction.

 

I wonder if there is a trick of filling the wood pours

on the concave side with 'something' permanent once the water

has evaporated.

 

I though I read that little beams in could be glued to keep it true.

Also, that 'steam' not water should be used.

 

Joe

[JimLucas]

My own advice is that you do nothing based on "I seem to recall reading somewhere" or other second-hand or hearsay advice. Unless you want to risk having to fix an even worse problem, follow advice only from those with actual experience in fixing this sort of problem.

 

I do not class myself among them.

 

...Good luck, though.

[Paul Read]

It may be better to take out the unevenness by adding chamois leather selectively. this is reversible and has worked for me in the past. It depends somewhat on the degree of warping. It may be worth investigating.

Edited February 4, 2004 by Paul Read

[duckln]

My own advice is that you do nothing based on "I seem to recall reading somewhere" or other second-hand or hearsay advice.  Unless you want to risk having to fix an even worse problem, follow advice only from those with actual experience in fixing this sort of problem.

 

I do not class myself among them.

 

...Good luck, though.

 

Jim, you're full of advice, thanks. That's why I posted my problem looking for such advice.

 

I've done some surfing. Other than Don N, on 'squeezer', citing that supporting blocks may by the basic cause, he doesn't give

a cure for the warp. I may contact him though, as he has always been helpful.

 

Checking rec.woodworking, rec.models etc, I came up with the following 'tidbits'.

 

#1 .... One thing you might try is to throw the boards out on a damp lawn for a

while with the cupped side ( presumably dryer than the other)down and

keep an eye on it. Grab it when it gets flatter and not only sticker it

but put some real weight on it until it reaches equilibrium ....

 

#2.....No kidding, but you might put it under the sun.

Heat causes the wood to expand, .......

What you're striving for is of course an equilibrium in moisture content.

 

#3....Chances are, that if it warped that bad, the wood is not stable and will

continue to warp no matter what you do....

 

#4....There are several techniques used to 'unwarp' wood. They range from

wetting the piece and clamping it in a brace for a while; to cutting

kerfs in the underside, forcing it flat then gluing wedges in the

kerfs...

 

#5....To start, normally warping is caused by the uneven drying of the wood. An easy

way to fix this is to heat the opposite side of the warp (the warp will

pull towards the dry side, so heating the "wet side" pulls the warp out), then

let it cool. The warp will not come back.....

 

I like #1 but don't want to wait till spring.

#2 sound reasonably safe, just put it on the window cell, inclined to the sun's rays.

#3 Always crape hangers around , but if I manage to straighten it, we'll see..

#4 1st sentence sounds like what Pete offered.

#5 I really like #5, now there's an optimist!

 

 

;<) Joe

[tomlaw90]

An old concertina handbook I have from about 25 years ago actually recommended sanding down the piece until it was flat again. Not an operation I would be inclined to try myself.

[VernLindquist]

I've fixed this problem myself on a few 20 key Lachenals.

 

For one instrument, the warping was a bit less than what you describe. I replaced all the chamois on the reedpan, adding an extra layer (skivved on the edges so that the "wedge" would leave a smooth top) on the sides where necessary to compensate for the warp. That seemed to do the trick.

 

Another instrument, which I currently have in hand, had a warp about the size you describe. I did steam it flatter (not entirelly flat, because the corresponding piece was not iself flat) with good results. I did it as follows: I took a wire rack and placed it over a pan of steaming (but not simmering) water. (The curve in the warp facing such that the concave bit faced down.) The warp reversed itself, and I then removed it from the rack, clamped (very carefully) the reedpan and left it overnight on my workbench. The steaming process went very quickly indeed--about 8 minutes or so. Even under the clamp, the warp reappeared somewhat, but it was lessened enough that I was able to add extra chamois, as above, to repair the problem.

 

I now keep a little humidifier (designed for a violin/viola) in my concertina case so that the problem won't happen to my good concertina!

[d.elliott]

Joe,

 

sorry to sound a little thick but, can you confirm that the reed pan is concave on the non chamber side? Also that you are stating that the pad board is convex when looked at from the underside (chamber contact face).

 

You don't describe problems with multiple notes sounding together with one key depressed, how have you established that this 'warping' is causing air loss?

 

Dave.

[JimLucas]

An old concertina handbook I have from about 25 years ago actually recommended sanding down the piece until it was flat again. 

Your smiley is the one known as "unsure". Good.

 

To compensate for reed pan warpage it's the side against the action board that needs to be levelled. That would entail removing the leather gasketing before sanding and replacing it afterward. Then the location of the support blocks would need to be adjusted to compensate for the sanding. That's not a trivial undertaking.

 

Besides, any warpage so great that it can't be handled by less severe methods would entail sanding off a lot of wood, which seems to me a bad idea.

 

In my personal experience, I've corrected warped reed pans simply by adjusting the heights of the support blocks, so that when the end was screwed on tightly (somewhat more tightly than necessary with an unwarped reed pan, the compression between the support blocks and the action board flexed the reed pan engough to straighten it out (even though it might still show warping when the pressure is relieved by taking the end off).

 

If any of the support blocks have come loose, they need to be glued back in the correct position, but those that are solidly mounted shouldn't need to be removed and reattached. Instead they can be built up by putting one or two layers of veneer (mahogany works well, and it takes so little) on the "top" side, where the reed pan rests. (It should never be necessary to lower a support block.)

 

This procedure has been adequate for all the warping I've had to correct in my limited experience, and that has included reed pan warpage of as much as 1/8". Maybe something more drastic would need clamping and steaming, but I can't advise on that, as I've never done it.

 

Compensating instead by using varying thickness of leather for gasketing strikes me as akin to using rags instead of putty to fix leakage around window panes. I wouldn't do it, though there are undoubtedly some who would.

[duckln]

Joe,

 

sorry to sound a little thick but, can you confirm that the reed pan is concave on the non chamber side? Also that you are stating that the pad board is convex when looked at from the underside (chamber contact face).

 

You don't describe problems with multiple notes sounding together with one key depressed, how have you established that this 'warping' is causing air loss?

 

Dave.

Dave

 

Yes, the pan is concave on the chamber side.

 

I was trying to practice a simple scale and watching

my 'chromatic tuner'. It took a full stroke to get a button

to sound and then it would indicate 1 note then a follow

on different note.

 

I'll attempt to send my first picture of the reed pan. I have

a wedge under it to lift it so that the two rails on the opposite

are on the plane on the table. The wedge measures a lift

of .210" which transforms to approx .105" middle warp.

 

Joe

[duckln]

Testing

[duckln]

Testing2

[Chris Ghent]

In my personal experience, I've corrected warped reed pans simply by adjusting the heights of the support blocks, so that when the end was screwed on tightly (somewhat more tightly than necessary with an unwarped reed pan, the compression between the support blocks and the action board flexed the reed pan engough to straighten it out (even though it might still show warping when the pressure is relieved by taking the end off).

 

snip

 

This procedure has been adequate for all the warping I've had to correct in my limited experience, and that has included reed pan warpage of as much as 1/8".

 

snip

 

Compensating instead by using varying thickness of leather for gasketing strikes me as akin to using rags instead of putty to fix leakage around window panes. I wouldn't do it, though there are undoubtedly some who would.

Jim,

 

with the caveat that I have never done it, this does not sound very practical, and I am amazed it works. An 8mm thick piece of wood with 10mm braces is being pushed flat by a 4mm piece (the action board) with a partial brace of another 4mm ? I would have thought even if you got some of the original warp out, part of it would have to be transferred to the action board. And too much pressure could spring some of the support blocks. Did your 1/8" warp not damage the action box?

 

In regard to the packing of the gasket surfaces, is this not a very reasonable interim suggestion as it is not interferring with any of the structural parts of the concertina? The fixing of the reedpan to the bellows hex (can I get away with calling this the "acoustic anchor"?) is through the reedpan supports. Obviously too large a gap to fill would be, well, too large. And you would need to change any environmental conditions that are creating the warp.

 

regs

 

Chris

[JimLucas]

...I've corrected warped reed pans simply by adjusting the heights of the support blocks, ....

with the caveat that I have never done it, this does not sound very practical, and I am amazed it works.

It should actually be possible to test the feaibility of the compression solution by placing the reed pan on a flat rigid surface (workbench, tabletop) placing a flat board over it, and pressing down evenly on the board. Increasing the pressure gradually should avoid any damage, since you can stop at any point. But wood is both strong and flexible; it is far less rigid than metal or ceramic.

 

An 8mm thick piece of wood with 10mm braces  is being pushed flat by a 4mm piece (the action board) with a partial brace of another 4mm ?

The total amount of warpage is distributed across the width of the reed pan. 1/8" across the approximately 6" width of a full reed pan is distortion of about 1 part in 50. If I estimate the lesser width of the 20-button's reed pan Joe pictured at about 4", that's still 1 part in 30, which I don't think is all that much. I don't think the amount of pressure needed to bend it back should be much, if applied uniformly across the width.

 

I would have thought  even if you got some of the original warp out, part of it would have to be transferred to the action board.

The action board's shape is constrained by the end bolts pressing its edges against the end of the bellows. Similarly, the edges of the reed pan are compressed between the support blocks and the edges of the action board. Any remaining upward pressure on the action board from the reed pan in the area away from the edges (1) is distributed across the chamber partitions, and (2) should simply press the chamber partitions and their leather gasketing tightly against the action board, preventing leaks, not creating them. Any actual distortion shouldn't even come close to being enough to have any noticeable effect on either sound or action.

 

And too much pressure could spring some of the support blocks.

It would take considerable force if they're firmly attached. There is also the option of mounting additional support blocks, but I haven't found that necessary.

 

Did your 1/8" warp not damage the action box?

No.

 

In regard to the packing of the gasket surfaces, is this not a very reasonable interim suggestion as it is not interferring with any of the structural parts of the concertina?

Varying the thickness of the leather -- and determining the right thickness at all points -- entails a lot more labor than shimming the reed blocks and making sure they're securely attached. Furthermore, I don't view my technique as "interfering with any of the structural parts of the concertina".

 

The fixing of the reedpan to the bellows hex (can I get away with calling this the "acoustic anchor"?)

I, for one, would not call it that, as its acoustic function is a matter of dispute.

 

Obviously too large a gap to fill would be, well, too large.

And my experience is that any gap that can be reaonably filled by additional leather can also be eliminated by flexing the reed pan back to "flatness", as I've described.

 

And you would need to change any environmental conditions that are creating the warp.

Warpage in wood is generally caused by changes in internal moisture content. Restoring the original moisture content, even if possible, will not necessarily reverse the warpage. On the other hand, the external forces of the action board pressing the reed pan against the support blocks are environmental conditions which are both significant and controllable. Still, keeping the instrument at a reasonable relative humidity is a good idea. (It's also a separate Topic.)

[JimLucas]

I have expounded on the technique of eliminating warpage by simply compressing the reed pan while it's in the instrument. But to some extent that is the normal state of affairs, the technique is essentially to increase the pressure that's already present.

 

So I wonder how much of the warpage Joe sees when the reed pan is out of his instrument is actually present when the reed pan is in place and the end is screwed on firmly... and therefore whether the warpage is actually the cause of the leakage he perceives. I.e., the reed pan is warped when outside the instrument, but is it warped -- and if so, by how much -- under playing conditions?

 

Wondering how to test that, I thought of the following:

..1) Cut a pice of heavy, compressible paper -- the colored stuff known in America as "construction paper" or "carft paper" -- to exactly cover the reed pan.

..2) With the reed pan in place in the bellows, place the paper cutout over the chambers and their partitions. Screw the end on, as you would normally.

..3) Let it sit for a day (sorry, you can't play it with the holes blocked).

..4) Open the end and check the paper for impressions of the chamber partitions.

 

I haven't yet tried this, but I expect that you will find such impressions. If they appear uniform, then that should indicate that the seal between the partitions and the action board is also uniform, whether or not it is entirely "flat". If the impressions in some areas are shallower or less distinct, then there might be leakage there. If any impressions are missing, then there is almost certainly leakage in those areas.

[JimLucas]

...the pan is concave on the chamber side.

Joe, doesn't your photo show the opposite? The reed pan is convex (higher in the middle) on the side with the partitioned chambers.

 

Joe, ... You don't describe problems with multiple notes sounding together with one key depressed, how have you established that this 'warping' is causing air loss?

I was trying to practice a simple scale and watching my 'chromatic tuner'. It took a full stroke to get a button to sound and then it would indicate 1 note then a follow on different note.

You say your 'tuner' registered two different notes, but did you hear two different notes? And did this happen with more than one button?

 

Note that if you can hear two different notes at once, you should be able to determine which notes they are, and that should indicate which buttons/chambers are involved in each case.

 

By the way, when the reed pan is set into the bellows end, does it fit snugly wherever it meets the walls? Space around the outside of the reed pan is a common source of internal leakage, and one that doesn't always result in double notes.

[duckln]

So I wonder how much of the warpage Joe sees when the reed pan is out of his instrument is actually present when the reed pan is in place and the end is screwed on firmly... and therefore whether the warpage is actually the cause of the leakage he perceives.  I.e., the reed pan is warped when outside the instrument, but is it warped -- and if so, by how much -- under playing conditions?

......

I haven't yet tried this, but I expect that you will find such impressions.  If they appear uniform, then that should indicate that the seal between the partitions and the action board is also uniform, whether or not it is entirely "flat".  If the impressions in some areas are shallower or less distinct, then there might be leakage there.  If any impressions are missing, then there is almost certainly leakage in those areas.

 

Jim

 

I did drop a 4' 'lego' through the bellows and with my calipers measured

the installed deflection at .084" at the middle of the board with 'lego'

resting on the edges. The uninstalled reedpan measures .105".

 

So happens that we have a package of 48 sheets of multi colored construction

paper, but it takes my finger nail to make a mark. I may try it again

later, and if just to see if and how bad the bellows leak (w/o the RP).

 

I can feel, with my finger tips, where the reed pan isn't flush with the

bellows. It's even on the R side, high in the middle, and low on the

L side. Measuring the block depths, the 11:00 block is down 1/32".

Not much maybe, but you can sure see it. I used a 6" steel ruler

to measure the block depths.

 

On a closer look, there is a gap between the F# and F(?) chamber, on the

outside wall. Also at 2:00 there are two pieces of 'leather' instead of chamois.

Otherwise the reedpan fits snuggly.

 

It's an Ebay concertina from Australia last tuned and repaired on 6/10/79.

 

 

Picture to follow.

 

Joe