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I have recently started using Mahogany for back braces on some guitars and was only using well quartered stock assuming the same principle applies to all braces. I recently noticed some photos on another forum where a very well respected builder was using Mahogany for back braces but the grain patterns appear to be very random and not quartered at all. Because of the density differences between spruce and Mahogany do the rules change?

T

since spruce is well know to have great directional strength, orienting the brace wood as we do makes sense. mahogany doesn't have the same properties though and i suppose one could get away with aligning the grain any old way and using off quarter wood, but it's not what i do. i tend to prepare my mahogany braces as i would do with spruce if for no other reason other then it sure makes planing them a whole lot easier and probably would help to prevent splitting in the future. i have no scientific data prepared on this to defend my position -it just feels like the right thing to do.

Besides what Arie says, Mahogany is quite stable when cut off quarter.
Tom

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because of the interlocking grain?

It definitely makes planing easier. I guess when you think of it's use as a neck wood not always perfectly quartered it would translate to it's use as brace wood. Hmmmm.

Arie: Not exactly sure but the low ratio of radial to tangential shrinkage has a lot to do with it. Mahogany has one of the lowest ratios of all woods.
Tom

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A person who has never made a mistake has never made anything!!!

I would cut two or three pieces of brace stock that are dimensionally identical, but with different grain orientations. Then I would deflection test the pieces to determine the stiffest one, then go with that grain orientation. I would recommend doing this for every bracing billet your about to use then cut it up accordingly.

Radial/tangential stability is not a concern for brace stock. Unlike a 16" wide plate, if a 1/2" wide brace shrinks in width, it doesn't cause any problems. And it's been fairly well proven that brace stiffness (in spruce) doesn't correlate very well to whether it's quartered, flat, or rift sawn. Probably the same for mahogany but I don't know for sure.

The main concern with brace wood is runout.

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