Flat Sawn Mahogany Top ??

[Fathand]

I wound up with an extra Honduran Mahogany size 0 back set but it is flat sawn. How viable would it be to use it for a top and build a 0-15 or 17.

I am not averse to using flat sawn on the back but the top probably should have more stiffness? If I go this route should I aim for a little more thickness to counter the flat grain?

[redir]

Mahogany is pretty dimensionally stable so you would probably be okay using it.

Ideally you would want to use measurements such as deflection testing to determine the top thickness. IOW thin the mahogany top out till you get the same deflection as a spruce top of that particular model guitar that works for you.

[John Arnold]

Mahogany is a diffuse porous hardwood. Unlike softwoods, hardwoods have cells that are roughly circular in cross section. That means that stiffness is not affected by grain verticality.
Slab cut will be a bit more prone to splitting, considering that the weakest plane is perpendicular to the growth rings. The most likely location of splits will be at the center of the cathedral, where the growth rings are tangent to the face.

[ProfChris]

Originally Posted by John Arnold

Mahogany is a diffuse porous hardwood. Unlike softwoods, hardwoods have cells that are roughly circular in cross section. That means that stiffness is not affected by grain verticality.
Slab cut will be a bit more prone to splitting, considering that the weakest plane is perpendicular to the growth rings. The most likely location of splits will be at the center of the cathedral, where the growth rings are tangent to the face.

Flat sawn mahogany will expand and shrink across the grain more than quarter sawn, around twice as much I believe. So you need to plan that into your design.

I've made one parlor size guitar with a flat sawn mahogany top (I have an old wardrobe which keeps on giving!). This was ladder braced with a floating bridge, and I built a dome into the top of just over 1/4 inch at the bridge location, reducing to around 1/8 inch in the upper bout. That was about 5 years ago, no cracks so far.

Top thickness was the same as for quarter sawn, pretty much. I thickness until I'm satisfied with the long grain stiffness.

I have found that flat sawn mahogany is a bit less stiff cross-grain than quarter sawn, though that varies for each piece of wood. Any difference is compensated for in the bracing, not by leaving the top thicker.

[Fathand]

Thanks for the replies everyone.