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After 70+ spruce topped instruments I am contemplating my first Mahogany top. Anyone have any good tips? Thickness? Same quality of wood as you’d use for a nice back? Voicing?

Thanks folks.

Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I work to deflection, so I treat it just the same as spruce. I’ve done two so far, and both are appreciably more resonant than, say, a Martin 17 series.

Good luck

Steve

^

Zackly.

So you guys are going to roughly the same deflection points as your spruce tops? What’s an average thickness for say an OM?

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Exactly the same deflection. I want the wood to have the same resistance to string tension regardless of species as a base, then adjust for taste/timbre depending on clients desire. That's why deflection testing is such a useful diagnostic tool. It gives you a baseline to adjust from.

I can't help with average thickness as the data is buried in a 400 page notebook and without knowing the serial numbers it's a crap shoot and I don't have time to dig.

The one I do remember, #20 so many years ago, was 2.75mm (.108"), but, of course, since every piece is different that's really not a helpful data point, so caveats to that.

I've often heard, 'just make it 20% thicker than spruce', but I've never thought that was a very good approach as the piece by piece material variance is so wide. Better to have data.

Sounds good, I have used deflection with good results for a long time with spruce. I'll just make sure I am .130 or more before I start testing. Thanks guys, that's pretty much what I needed to know.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I measure wood properties, and use that to determine the 'correct' thickness. It's an equivalent approach to deflection testing.

What I've found is that most hardwoods, mahogany included, tend to have a Young's modulus along the grain that's more or less in the range of spruce, but the hardwoods are much denser. Young's modulus (E) is what determines the stiffness at a given thickness: two pieces with the same E value will have the deflection at a given thickness. Without actually measuring something, either the E value or a deflection, you can't know for sure. Some people are very good at 'measuring' stiffness by feel, but some tests I've been told of caution that most folks are not nearly as good as they think they are.

At any rate, if the E value of the wood you use is like spruce, then you'll need to leave the top as thick as a spruce top to get the same stiffness. Since mahogany is generally denser, the top will be heavier than a spruce top would be. This will tend to cut down on power and treble response, but give you more sustain and 'headroom'. The penalty is less with a smaller body, since you can make the top thinner.

Not everybody works hardwood tops to the same stiffness as softwood ones, making up for it with heavier bracing.

A wood to consider as an alternative is cedrela. I've made a lot of cedrela top guitars now, and it looks a lot like the khaya back and sides I use. That way you have the look of an all mahogany guitar, but cedrela is a lot lighter than mahogany, which I prefer.

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nigel

http://www.theluthierblog.com

"Same quality of wood as you’d use for a nice back? "

Some mahogany is lighter in weight than others, so if you have a less dense piece I would be inclined to use that and brace accordingly. Part of the "charm" of a hardwood top is that they don't sound like spruce.