28b Lachenal air tightness issues

[Oberon]

I am having a helluva time with this 28 button lachenal concertina I just acquired.
I've a bit of experience working on them, but this one is giving me a run for my money so far.

Two support blocks, one for each end, had been rattling around in the instrument, one was loose. As a result the reed pans were both warped (not too severely) and the corresponding action boards are convex, but seem to flatten under bolt pressure.

Whoever owned this before used neoprene gaskets to take up the slack in the ends from the warped reepans and it worked a little. The instrument is hemorrhaging air, and I get about 12 seconds to full extension in a drop test. Someone attempted to patch cracks in the left hand action board but they're not great and they're pretty hideous 'repairs', honestly.

I've flattened the reedpans successfully following advice of some very kind folk, and I buffed up the chamois to see if it helps the seal. I then affixed the support blocks back into place and raised the reepans to be flush with the ends.

No dice really.
The neoprene gasket prevents any sounding of multiple reeds at once, so it's doing an ok job there, but there is a lot of air pressure loss happening here. I also patched some obvious leaks in the bellows and have only found one more small leak that I can detect. There are existing corner patches as well. They're not attractive but they seem to be doing the job.

I've ordered in some new pads to see if that's the issue, but I feel like the current ones arent doing a bad job, but I suppose it's worth ruling out. I also ordered new valve material in, though the current valves seem largely ok. Almost every reed needed to be shimmed with paper to get them to stay in place.

Currently the instrument is not in acceptable playing condition. I cant get a decent phrase of playing out of it without having to draw on the air button immediately.

Should I replace all chamois? Ie- bellows end gasket, reedpan gaskets? It's old, its compressed and I've attempted to bring it back up but its not great.
The reedpans are now level with the action boards but if I do not use the makeshift neoprene gasket I get multiple notes sounding, which tells me that the action boards are not actually level enough or the chamois is not cutting it at present.

For reference, Ive read every article I can find on the subject on this forum, and I've used Dave Elliots book for the past couple of years for working on my concertinas. Does anyone have any other advice? I would like to see if theres something I've missed here. I'll post photos for reference when I can. Thank you kindly!

[Theo]

Before going to the trouble of replacing all the pads, you can make yourself a very simple device to test the pads in situ.  A tube with one end wide enough to fit over the hole in the pad board.  Place over the hole, place the other end in the mouth and blow. You will hear air escaping through leaking pads.

[d.elliott]

You can hold the padboard, with the action box cover removed, up to a bright light and look through the pad holes at the pads against the light, it will not test spring pressure but it will identify pad misalignment etc. You can also put a bright LED lamp in the bellows and identify lots of small holes that can add together as the equivalent of a wacking great big hole.

 

If you are unsure about the effect of the warped reedpans, assemble the instrument without them and see what difference it makes.

 

Dave

[Mike Jones]

I had a similar problem some time ago with a 26k Lachenal. I  performed the actions described by Theo and Dave elsewhere and found a couple of pinholes which were patched but without much change. Then I swapped the reed pans with another concertina and the same problem persisted but the  "problem"reed pan worked OK in the other 'tina which seemed to indicate that the reed pan was not the issue. Looking at the problem box again I thought one of the corner blocks I had replaced was slightly too high and so carefully trimmed it with a sharp chisel rather than remove it and re-glue. Eventually I got it so the leaks were  reduced and a thin piece of chamois from an old gasket glued to the top of the block solved the problem. Whether this was also due to air leaking past the corner of the reed pan in that position too I don't know, but I now have a working 'tina again.

 

Mike

[Oberon]

Thank you for your input, folks, it's very much appreciated. 

 

I will construct a tube like the one linked to in order to check the pads. Whoever made these pads cut them at angles and they're not really great, so it's in my best interest to replace them anyway, I'm sure. 

 

I used the flash light trick as suggested and it did help me identify another small pinhole in the bellows so thank you for that! The holes I've been finding seem to commonly be at the gussets. Its causing me to wonder if the gussets are coming lose, as this is the second one where the gap was at the gusset under the card hinge (from the inside perspective). I skivved a patch and used a flexible pva to attach it and it seems to be working well enough. 

Also, I'll try not installing the reedpan as a control, thanks dave, I hadnt considered trying that, yet it seems so obvious, haha.

 

I did identify another leak now, of course. A corner edge of the right hand end seems to be leaking at its interaction with the corresponding bellows end. I had this same issue occur on the left hand before, but roughing up the chamois seemed to fix it, however that is not working on the right hand. I checked to make sure the reedpan was level, which it is, but something is certainly off if I'm getting a corner leak. 

 

Mike, I did a similar thing with the left hand end yesterday. A support block was a tad high and rather than try to knock the block off to re attach it, I used a very sharp and short knife to slice thin layers of wood away, lowering the reedpan. Seemed to do the trick! 

 

I'm finding that many of the roadblock supports have been loose. Someone really mustve wrenched down on the end bolts to get a more airtight seal, but it's done the instrument no favors, that's for sure.

 

Thank you gents, I really appreciate the advice. It's quite indispensable!

[Oberon]

Alright, I've some new questions as I havent been able to find specific answers for these here on C-net (though I could be missing them for lack of proper wording).

 

 

 

1) the previous 'repairer' used paper shims that wrapped around the entirety of the reed so that they would stay snuggly in the reed dovetail slot. I believe the pressure of the paper running in line with the reed is somehow exerting that force at the reed shoe vent/slot, causing a foul when the reed cycles. I can hear a metallic sound in this case and its affecting a number of reeds that are held in this manner.

Why is this? Is it possible for the brass show to be compressed enough by these forces as to effectively distort the reed vent/slot? Should I instead add paper to just the front and back areas of the reed shoe instead to avoid this?

 

2) I will need to make new valves and have been in contact with sandylaneman on Ebay who will sell me the leather I need to make the valves. 

I've just bought pre-frabricated valves before from concertina connection, but am interested in the valve making process this time around  

So,

How do you cut your valves for this purpose? Do you have a die/punch that cuts the shape or should I get use to a razor blade for making the valves themselves. 

 

Please tell me if I should start a new thread instead. Thanks!

 

Edited December 28, 2019 by Oberon
Grammatical errors and refinement of syntax

[Wolf Molkentin]

2 hours ago, Oberon said:

Is it possible for the brass show to be compressed enough by these forces as to effectively distort the reed vent/slot? Should I instead add paper to just the front and back areas of the reed shoe instead to avoid this?

Yes and yes - try that, but just with the affected reeds.

[Chris Ghent]

The reeds which are making the metallic noise, can you look at them with magnification and backlight? They may be off centre in the frame. While reed frames can be distorted by side pressure enough to foul the reed it has to be an extreme case to foul in a Lachenal anglo as the clearance between reed and frame tends to be large in them. An off centre reed would make it more likely. You might also be able to see witness marks in the reed slot where it has been hitting.

[Oberon]

Chris,

 

I had the ends off a couple hours ago to check for that very thing but the reeds didnt seem to have debris/burrs and were aligned well enough I think. I'll try with the light box to be sure though.

 

I did, however, notice that it was mostly the right hand that suffered the most from the metallic 'tinking' sound and slow and weak note initiating, and coincidentally enough, the reeds on this side were the tightest and most heavily shimmed. The left hand side had much fewer shims and the reeds seem to fit solidly in their slots without the need for shimming. 

 

I didn't have time to adjust the shims today (ie remove them and add thinner pieces, not following the entire length of the reed) but I'll try tomorrow to see if this has an impact. 

 

I've improved the air tightness a good amount so far. It started at 12 seconds to full expansion, and now it is up to 20 seconds. The reeds on the left hand play with acceptable speed now and sound good, whereas the right side reeds are weakest on the push notes and rather feeble in attack. 

 

I have yet to get to a point in the repair where I can do without the neoprene gaskets, even though I've leveled out the reedpans, as I'm going to be replacing the entirey or the chamois on the dividers, but I cant imagine these gaskets are entirely responsible for the reeds response and voice. 

 

The current set on reed height is decent and shouldnt be causing this slow a response in my experience, which is why I wonder if something odd is going on. 

 

 

 

 

 

[david robertson]

Returning to the air-tightness issue, the one obvious thing that no-one seems to have mentioned is the possibility of leakage around the edges of the reedpans. If the chamois seals are old and compressed, there's a pretty good chance that they won't be doing their job properly. In the worst case, you'll be able to see the gaps just by moving the reedpans by hand, but even if they're not that loose, go round the edges with a 15 thou feeler gauge. If there are places where you can slip the gauge in, you need to lift the chamois seal and glue in a strip of thin card underneath to take up the slack.

[Oberon]

David,

 

I had read up on that fix idea from a thread elsewhere on this forum and figured it was worth a shot, as I found the right hand reedpan was indeed a bit loose. 

First I had tried to pry the chamois up but it was not coming up at all. I fear that it will tear if I attempt to lift it. 

I do have 3 sq ft of chamois and am in the process of replacing the reedpan divider chamois, and could likely replace the bellows end chamois, but I've never done that before and cant detect where the leather ends and the chamois begins. 

 

If I can manage to pull up the chamois without tearing it, I'll shim it. For now, I'd wrapped an ultra thin layer of chamois around the entirey of the reedpan and pressed it into the ends and it fit quite snugly and didnt seem to leak, from what I can tell, but that's a very temporary stop gap. 

 

I've tried finding articles here that detailed replacement of the bellows end chamois but cant find anything with much visual detail. I referred to Mr. Elliots book but I cant find any section on its replacement unfortunately 

 

Any ideas on how to remove/replace this gasket?

[david robertson]

3 hours ago, Oberon said:

David,

 

I had read up on that fix idea from a thread elsewhere on this forum and figured it was worth a shot, as I found the right hand reedpan was indeed a bit loose. 

First I had tried to pry the chamois up but it was not coming up at all. I fear that it will tear if I attempt to lift it. 

I do have 3 sq ft of chamois and am in the process of replacing the reedpan divider chamois, and could likely replace the bellows end chamois, but I've never done that before and cant detect where the leather ends and the chamois begins. 

 

If I can manage to pull up the chamois without tearing it, I'll shim it. For now, I'd wrapped an ultra thin layer of chamois around the entirey of the reedpan and pressed it into the ends and it fit quite snugly and didnt seem to leak, from what I can tell, but that's a very temporary stop gap. 

 

I've tried finding articles here that detailed replacement of the bellows end chamois but cant find anything with much visual detail. I referred to Mr. Elliots book but I cant find any section on its replacement unfortunately 

 

Any ideas on how to remove/replace this 

I have a special bodging tool for just this job... an old teaspoon with the handle end ground to a bluntish edge and bent up through 90°. The sharp edge is inserted under the chamois, which can then be prised up.

If you're replacing rather than shimming the seals, cut strips of chamois a bit wider than necessary, and first glue them to the inside of the bellows frames. Then go round with a hole punch to make the holes for the end bolts, before stretching and gluing the chamois over the frame edges. Press the frame down on a cutting mat, outside edge down, and use a scalpel or craft knife to trim off the surplus chamois.

You will then have to re-bind the bellows ends in leather, in order to cover the exposed edges of the new chamois seals.

[Oberon]

Ahh that tool sounds quite useful indeed. I'll have to make one very soon! The chamois very likely should be replaced but I'll try shimming them first. 

 

 

Edited January 21, 2020 by Oberon