Old Gibson with Cedar Top

[mandotool]

1 additional example of a Sycamore? back on this 1904 Gibson A3..

[Spyder]

Most Gibsons built before the mid to late 1920's had birch [not beech] back and sides, except for F-4 and F-5 models. I suppose beech could have been used on an early model, but I have not heard of it before.

It looks to me like the top damage was most likely caused by external pressure. It could have been smacked hard with a hand, stepped on by a toddler or a pet, closed up in a case with too much stuff piled on top of it, or it could have been in a case that had a heavy object dropped on it, or that was sat upon. I don't think it was hit by a solid object, at least not while it was out of a case. I don't see any obvious signs of impact.

The earlier repairs probably failed because there are cross grain fractures that were not reinforced after they were glued. Cracks along the grain often do not need to be reinforced, but cross grain top fractures should always be reinforced. The reinforcements should overlap the crack[s] by a 1/4" to 3/8", with the grain running perpendicular to the crack. They can be worked down to 1/16", perhaps less after they have been glued in. A reinforcement similar to a violin "soundpost patch" might be appropriate on this particular instrument.

It looks like you've got enough beech there to reinforce side cracks on several dozen mandolins.

I think the last owner actually thought it was stepped on. he went on a business trip, and when it came home, it was cracked. This was after having some cracks repaired in the past. But his wife insisted it stayed in its case, in the closet the whole time. He didn't believe her, so who knows.

I have now added little patches to cover all the cracks in the top, and have started rebuilding the sides. Now I am starting to wonder if the damage wasn't really caused by weak sides. These are terrible! Too thin, and very brittle. I have to be careful handling, because the sides split so easily.

So, if this is sycamore, does anyone know if that wood tends to get more brittle with age? Or need to be thicker to begin with?

[Spyder]

Here are some additional pictures of the side wood. You can see the grain pretty clearly, I hope. The pics show one piece that broke out of the side, and the same section after it was glued back in place. Another pic shows the back, with some pieces of beech that will be used to make new sides to fit inside the original ones to strengthen them.

[CarlM]

Have you been able to get thickness measurements on the top? The reason I asked is that cedar tops need to be thicker than spruce tops and if it is not that may be contributing to the failures.

[Spyder]

I don't have a way to measure the thickness of the top and back just now, will have to come up with something. But both feel quite strong and stable, and I have not been able to see or feel any deflection in the top cracks when flexing.

The sides are a different matter. Thickness at the head block is around .042", tapering to approx. .094" at the tail. at the center, thickness is in the area of .062". The weakest point is where the side with the hole busted out connects to the head block. I suppose this was done while final sanding, but the side was around .030" thick at this point. And it failed, in the same area as the wide grain on the top.