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I’m building an OM with a traditional Martin X-bracing pattern and tapered braces, which (surprisingly) I’ve never done.

Trying to take a beginner’s mindset to this: is 1/2” a good starting height for tapered tone bars?


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Yes.

Thank you. [PERSON WITH FOLDED HANDS]


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I might start out a bit higher, but that's usually close to where I end up. With tapered bracing, tall at the bridge, the X crossing will generally be just a bit lower than the high point. Reinforce the joint, of course.

Thanks, Alan.


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From the build guide we used with students... sort of conforms with Martin and similar practice. These are definitely milled dimensions versus finished, and for scalloped and tapered bracing. For the late 1940's tapered bracing, I've seen tone bars and fingers which were considerably taller - closer to what was a relatively briefly popular use of so-called 'parabolic' bracing. I would suggest adding an 1/8" in height to the tone bar number and start at 7/16" height for the fingers, expecting both to be taken to a profile more like those rather sharp-edged Gibson braces from the 1930's and 1940's.

There are some good bracing threads on UMGF that show classic tapered bracing shots for D and some 000/OM and 00. These threads are worth a look to get an idea on what the actual bracing looked like during the relatively brief period Martin used the scheme (late 1944-1949, and into the 1950's for tone bars and fingers - see the 1950 00-18 shot below...and those diamond cleats are not mine, although they are stable and the top looks pretty good).





A word or three on finished dimensions: An example would be the center graft on the back - these were installed at the milled dimensions, but were then planed to about .100" before further planing and sanding to the typical profile seen... finished dimensions were closer to .090-.095" x .740" following final work to clean up any edges with a shoulder plane (prior to cutting the brace channels) and finish sanding. Final dimensions are usually determined by the voicing process, with that reflected in the table above as more or less a maximum dimension from which to start whittling away.

Bump

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Say what you do, Do what you say.

Remember that the tone bars don’t do all that much to take the load which is on the top and x braces mostly. So half inch is ample. With all the usual caveats about how it’s all a system and isolating one aspect etc etc.

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One thing leads to another

I'm doing the same thing- first OM build and have several plans (StewMac and GenOne), with differing brace dimensions.
I'm filling in the table with the dimesnions from the plans as I go, so it's not complete yet. I'm using the SM dimensions thus far. The dimensions are the finished size and they match the full-sized drawing "templates".



Attached the working table: OM vs 000 vs Dreadnought Brace Dims (Typical / Reference Values)

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Measure Twice,

Karl Borum

Thanks, everyone! Much appreciated!

My previous guitars used either a lattice or slightly shorter, parabolic braces below the X, so it's just a different approach to try and I want to lean into tradition a bit.