Repair To Broken Action Board

[Alex West]

I'm about to start on some serious woodwork repair and thought I'd run my thoughts past the forum.

 

This concertina came in a pretty shabby looking state but after disassembly the reeds seem good, the levers are OK, the bellows might be rescued so I think the instrument is worth trying to save rrather than use as a donor; the only trouble is the woodwork, of which this repair described is the most serious issue and one I haven't tackled before.

 

I'm proposing to repair the action board by carefully routing around the existing massive cracks to get back to solid wood and fit in a new section of 3mm thick mahogany to restore stability and air-tightness to the action pan. The new section will have a step in it so that there'll be a mechanical joint but (if I get it right) there'll be no gap on either top or bottom of the board.

 

The attached photos show

1. The underside of the action board where the central piece of wood between the red tramlines is completely loose and very flaky
2. The corresponding upper part of the action board
3. The top hat section I'm proposing to let into the action board (roughly where the tramlines are)
4. The top hat section laid over the split where I'm proposing. The narrow section of the top hat will go right through to the upper side and I'll rout the action pan halfway through so that the broad section sits in a channel
5. A completed repair on a similar board I did earlier. This repair wasn't full depth and the board crack wasn't so compromised

I've tried something similar but not so extensive on a previous repair and it seems to have been successful as the last picture shows.

 

What do you think of my proposal? The cracks aren't neat enough to be able to sand back and fill with thin shims of veneer and the wood seems pretty unstable - the mahogany they used may just be getting old but it seems rather soft compared to modern materials. I want the repair to be going back to solid wood without taking too much away of the original board (to preserve as much as possible of the fabric and also ensure dimensional consistency.

 

Is there a neater/better way of achieving the repair?

 

Alex West

[Theo]

Your last repair looks very workmanlike. Has it lasted ok? If so why not do it again?

 

Looking at your other photos reminds me how much I hate having to deal with old half-baked repairs.

[d.elliott]

A similar approach to my own, I prefer to hand cut to reduce strain on the overall assembly, and I use a dove tailed slot and matching insert to avoid precision issues. The key thing is to use wood of the same hardness as the parent wood, as close as possible anyway., helps with blending and sanding. Also try to match the lay of the grain as well as just the direction.

 

Dave

Edited January 26, 2013 by d.elliott

[david robertson]

Your own technique seems to produce excellent results, but for someone without your woodworking skills (me, for example) Dave's technique is simpler. Fix your new timber over the old (a couple of temporary screws will do the job), set your scroll-saw at an angle of 3 or 4 degrees (experiment first), then cut through both old and new together. The result should be a perfect fit, even if your cuts aren't perfectly straight.

[SteveS]

Fix your new timber over the old (a couple of temporary screws will do the job), set your scroll-saw at an angle of 3 or 4 degrees (experiment first), then cut through both old and new together.

I find veneer tape (as used in marquetry) is useful for holding the job in place - once affixed it doesnt stretch or move, and can be easily removed afterwards.

Edited January 26, 2013 by SteveS

[Alex West]

Thanks for your thoughts chaps; I like the idea of dovetails and I might give it a try. 2 problems with the scrollsaw approach for this particular job

1. To be able to use a scroll saw, I'd have to remove one of the side pieces to the action box and I'm relying on that to give the base board some stability
2. I don't have a scroll saw

I'll let you know how it goes

 

Alex West

[Alex West]

Well, I think I'm at the end of this stage of the repair; here's the finished result:

 

 

It wasn't as straightforward as it might have been. The top hat went in very easily (I used dovetails on the lower part of the top hat) and I filled the largest of the other cracks quite simply but as I filled the smallest of the cracks with a slim piece of veneer and clamped it up, the clamp slipped and a considerable part of the action pan split. My repairs were fine, the glue being stronger than the wood, but the original action pan is very soft and fragile. After crying and swearing (a lot) I was nearly contemplating replacing the whole of the action plate with a new piece of mahogany but taking it slowly, glueing a piece at a time and taking a bit more care over clamp selection and placement paid dividends

 

All back together now and waiting for the rest of the repairs to catch up (bellows, bushing board and normal refurbishing stuff).

 

Alex West

[Marien]

Alex,

 

As you say: "My repairs were fine, the glue being stronger than the wood, but the original action pan is very soft and fragile."

 

I have a similar action board split on an old lachenal, not as big as yours so I am not adding a new wood strip, but it has weak spots away from the crack, on different points of the action plates. I can see the weak spots. Light is coming through when I hold it against the day light.

 

I am wondering how to repair the wood. I am thinking about using a glue while sanding it flat - so the wood will fill the weak spots and the glue will make it air tight. Does this make sense?

 

Another thing - just wondering - what glue did you use?

 

Thanks,

Marien

[Alex West]

Marien

 

In Theo Gibb's "Workshop stories" on his website (http://www.theboxplace.co.uk/workshop-stories/), you'll find a small photo-essay on repairing cracks in a Lachenal action pan and perhaps this is what you're going to need.

 

If the cracks have been caused by the wood drying out over the lifetime of the concertina and the instrument is now in a stable humidity, they aren't going to close up again so there'll always be a weakness there unless it's repaired. ( I've seen cracks close significantly if the instrument has come from the US to the more humid UK but I've still completed the process by glueing in a repair strip). There are resin treatments which you can apply to old fragile wood - typically rotten window frames! - but I've no experience of using them for musical instrument repairs and I don't think I'd like to try.

 

Maybe your "weak spots" aren't reducing the structural strength of the pan by much, but I'd suggest that filling them with sawdust & glue is just plastering over the cracks and isn't going to give a neat solution. Even if it does make it air-tight, it's only going to be a surface coat so won't give support through the thickness of the pan woodwork (circa 3mm?). I've used a paste of sawdust and glue myself in certain circumstances, for example to fill small gaps, surface defects, hollows and joins in non-critical locations and it can give a smooth finish, but I wouldn't expect it to substitute for a proper structural repair.

 

For this type of woodwork repair, I mostly use ordinary (yellow) Titebond, an aliphatic resin glue, but I sometimes use Veritas "Chair Doctor" - again an aliphatic glue but less viscous for getting into narrower cracks.

 

Alex West

[Marien]

Alex

 

I think Theo's way of filling the cracks with slips of wood is just what I need.

 

The weak spots are just dots where the wood is thinner, They don't weaken the overall structure of the plate.

 

Thanks for the information, I guess I'll stick to Titebond.

 

Marien