Monday, October 01, 2012

Thoughts on X-bracing

Sean’s twin-point is going through that process of waiting for the polish to harden and the Standard Plus is being polished. That’s happening in parallel with construction of John’s twin-point’s soundboard.
The vast majority of steel-strung, flat-top instruments use some kind of variation of X-bracing. The X is the main structural support of the soundboard and therefore needs to be strong; however for an instrument to be responsive it also needs to be light. Here’s how I do it.
Firstly, some accurate marking out is called for-
Then the notch has to be cut-out; use a razor saw for this to get a really clean cut.

After a chisel has been used to chop the waste out, I use needle files to clean up the notch. 
A notch is cut in both of the braces that make up the X. You might be able to see that wood has compressed slightly due to the tightness of the joint.

This is what you are after-
When you cut out the notches, it is important that you get the depth of them spot on. Too shallow and one of the braces will not make contact with the soundboard. Too deep and the bottoms of the notches will not touch each other; remember that this is the only point on the X- brace where end-grain is not involved in the joint and you want to get the maximum benefit from it.

I like to glue one brace on first…

...and then the other- notice that I prefer to use clamps rather than go-bars- once the glue is on, these joints are so tight that you need the force from the G-clamp to press it fully home.

In order to re-enforce the joint a patch of spruce is glued on the top. I hate seeing the X reinforced with a piece of muslin soaked in glue!
Note that throughout this process the braces are left square; only once the patch is glued on, do I profile the braces.

Now this is a very pedantic way of doing the X, but if you are going for lightness in construction you must build with the utmost accuracy if you want your instrument to last.

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Blogger Wood With Strings said...

Gary, I recall noting that the tap tone of a recent guitar top was significantly different once I'd bridged the X joint as you've shown here. It highlighted for me just how much that seemingly insignificant sliver of spruce contributes to the overall stiffness of the top!

2:23 am  

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