Corner blocks at different heights?

[RWL]

In my previous thread about air leaks in the chamber, someone suggested that a corner block might be loose or require a shim. I opened it up again and it looks more complicated than that as you can see from the photo below. The corner blocks are all at different heights from the top. One corner block is completely missing, so I don't know what height to make that, and one has been moved, apparently to allow a gusset repair. Are the corner blocks supposed to be at different heights? How do I deal with this?

 

 

Also, I checked pad board for flatness. The center is slightly higher than the corners in all directions.

[Geoff Wooff]

You will need to measure the total depth of the reed pan at each point because the block heights will have to corespond in such a way as to support the reed pan when it's top surface is flush with the end surface of the bellows frame. All the Chamois gasket surfaces need to connect with the pad board to make a good seal.

 

Also make sure that the moved block and the replacement block do not foul a reed that is close to the edge. Sometimes these corner blocks are not in the corners for that reason.

 

The different heights are to allow a level end surface with a 'Canted' reed pan... that is a reedpan where the chamber wall heights are shallower at the high

notes and deeper for the lower notes.

 

With the pad board you say that the centre is higher than the edges all around, do you mean that when you place the straight edge across you can see light

between the straight edge and the board in the centre (concave board) or at the edges (convex board) ? If the deviation from perfectly flat is only slight

then I would not worry about it. If there is much curvature then check the 'fit' between the padboard surface and the reed pan by placing the two together and

seeing if the surfaces 'mate' together... at the edges by looking for light showing through any gaps at the top of each chamber wall... at the centre by holding

the two pieces together and seeing if you can slip something thin between them at the centre, working through the central hole of the reedpan. A Feeler gauge

or a very thin stiff piece of card/plastic.

 

Usually the chamois is sufficient to close any small iregularities. An allowance has to be made for the fact that the end bolts can have a modifying effect on

the shape and press the two surfaces together.

 

Sorry it all sounds too technical and in reality if you get the bellows blocks to support the reedpan so it is is level with the bellows frame it is probably

all you will have to do to cure the problems.

 

I have noticed that in a concertina where the pad board exerts a small amount of compression presure onto the reedpan the instrument plays better and sounds better. So, either a perfectly flat padboard mating to a perfectly flat reedpan or a pad board that will meet the reedpan firstly in the centre and then the end bolts will pull the edges of the board into contact with the reedpan.

Edited August 14, 2012 by Geoff Wooff

[Theo]

If you look carefully in the corner with no pan support block you should be able to see a mark left by the glue which will show where the block should go.

 

As you can tell from Geoff's post above, getting a reedpan correctly supported is rather a subtle operation, so be prepared for some careful detective work, take your time, and don't be surprised if you don't get it right first time.

[apprenticeOF]

I find it useful to use vernier calipers for this. I measure the overall thickness of the corner corresponding to the missing block, compressing the chamois slightly, then lock the position with the caliper lock screw. The depth measurement is then precise from the tail of the vernier to body, and is easily transferred. I've yet to have any problem positioning the blocks this way.

 

Doug

[Chris Ghent]

An easy way to get the reedpan back where it belongs is to put the reedpan in place, invert the bellows on a flat surface, put your hand in the other end and push the reedpan down so it is flush with the flat surface, and then fit the blocks from the back. I usually do it one block at a time so I can pull the reedpan out and make sure no glue has fixed it in place. I also have a tool to put pressure on the block ( rod with a screwdriver-like end bent over at the tip), it is difficult to do with a finger as blocks usually have a sharpish corner and when putting enough pressure on the block it attaches to your finger and pulls back off when you take your finger away.

 

Slightly more complicated when there is a bow in the reedpan because you have to make a ring of cardboard a little narrower than the edges of the reedpan and high enough to keep the centre of the reedpan off the ground. I have only done this once with a bow in the pan, it was very slight. It makes more sense to fix the bow.

 

Cheers

 

Chris

[RWL]

Thanks to all of you for your comments so far.

[Geoffrey Crabb]

A little belated but may be of interest

 

Geoffrey

[RWL]

A little belated but may be of interest

 

Geoffrey

 

 

Thank you. It contains basics that are helpful to know.

[RWL]

With the pad board you say that the centre is higher than the edges all around, do you mean that when you place the straight edge across you can see light

between the straight edge and the board in the centre (concave board) or at the edges (convex board) ?

 

 

I have noticed that in a concertina where the pad board exerts a small amount of compression presure onto the reedpan the instrument plays better and sounds better. So, either a perfectly flat padboard mating to a perfectly flat reedpan or a pad board that will meet the reedpan firstly in the centre and then the end bolts will pull the edges of the board into contact with the reedpan.

 

 

 

I can see light between the periphery and the straightedge - the pad board is convex. Sounds like this is a good thing.

 

 

Follow up for all of you who contributed. Three of the corner blocks were loose and one was missing entirely. I glued the loose ones and added the missing one. I finally reassembled it this evening and the air leaks are fixed. Now I need to replace 17 valves on the right side. The left side is playing OK as it is, so I'm not going to pull the end off and potentially create new problems. That's how I wound up with problems on the right end - I took the reed pan out because some notes weren't sounding in certain directions. Thanks to all for your suggestions.