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Looking for a tip here. I've done these types of repairs many times but this one is a slight bit different. The crack starts in the lower part of the upper bout and reaches all around almost to the tail block and runs almost the whole length along the linings. The way I would normally handle this is to knock out a kerf about every 2 inches so I can get a cleat in there and then just use a tuner clamp to align the cracks and then spool clamps to close them.

I've been blessed as a guitar repair man with long skinny arms but I simply cannot reach far enough back to knock out some linings in the lower bout.

Any suggestions? I really feel like cleats are necessary for a repair like this. Incidentally it's a Martin guitar and the cracks went right by the side reinforcement. I think an improved design would be to embed the reinforcements at least 1/4 in below the line that the linings make. Then it might actually stop such a dreadful crack.

Have any of you made a specialty tool or can think of one?

If I simply cannot reach around to remove linings is it even worth putting in a cleat flush to the linings?

Regards.

I have been having good luck lately using strips of tight woven cotton to reinforce things like this. I got the idea from an old violin repair guy. I use the same cotton I buy for the covers on my french polishing pads. I soak the strips in water and wring them out then smear fish glue on one side and plaster them across the area and press them smooth. You can double them up and if cut at a bias will be quite strong.

I also have quite few surgical tools that I use. These are particularly handy for jobs where you must reach the tail block area.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

When you say "cut at a bias" do you mean so that the weave of the cotton goes across the grain? I just use old t-shirts for FP covers, where do you get this cotton from? Also, what does the water do? Is it good enough to just press in place or do you need some sort of clamping pressure?

It's a good idea I like it.

Bias would refer to a repair with a double layer of fabric. One layer would be cut with the weave running at an angle to the other. I have been cutting small strips about 3/4 x 2 inches or so. Anything larger is very messy to try and place inside the box and smooth. The water softens the fabric a bit as it is quite stiff for the job as is and it helps get the glue to penetrate the fabric entirely. I buy a few yards as needed at my local fabric store, the right weave cotton for my FP pad covers (and now this) and flannel for the core. A proper pad makes for a better FP IMHO.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Sorry, forgot to mention that the cotton I use is not like T-shirt material but rather more like that used on a nice button down shirt.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

are these types of brutal side splits mostly seen on rosewood...? (looks like rosewood in the picture)

Hey Filippo I'm always a bit weary about using CA for a job like this because of staining and also because of the instant dry time. When you use CA to you first tighten up the crack and then wick in thin CA? Kind of like the binding construction method where you tape up the binding then wick in CA and it's done?

Do you need to do some substantial finish work to hide the crack if you use CA? I was going to use fish but I do like CA for a lot of repair work just not so much on the visible side of things.

nyazzip this guitar is Rosewood but I don't think it's particularly special in any way. I've sen cracks in mahogany, all kinds of top wood, and other woods as well. If it's a nice quarter sawn piece with no run out the crack will travel. And like I was saying in my first post if the side reinforcements were let into the linings a bit then I think it may have stopped the crack but this one ran right along the full length of the linings.

not to go off on a tangent here, but....i have just realized (finally) that quartersawn wood is much more prone to splitting. makes sense, i just never thought about it. so: i understand why it is good for a top and back, for stiffness....but is stiffness important for sides? if not, then why not use flatsawn wood for sides, which should be much less likely to split...?
just curious

Flat sawn is harder to bend especially on a pipe like I do. Also quarter sawn is more stable. There is less movement across (perpendicular) to the annular rings. So for a given x,y,z coordinate of a quarter sawn plank of wood if x is the width y is the height and z the length. then it will expand more on the y axis then on x.

So a flat sawn side would expand and contract more towards the top and back of the instrument than a quarter sawn one.

But you are right it would prevent cracking for sure and that is a good argument to like laminate sides.