Guitar Top Bracing

[Telenator]

I am about to start bracing the top for my Guild D15M and I've been reading a lot about "arched bracing" verses flat bracing.

The arched bracing has one shaping the bracing surface to a 30 ft radius and then setting the top in a bowl with a 30 ft radius in order to slightly dome the top.

Have any of you guys found an advantage to this over simply doing it flat?

 

[chazmo]

Hmm... Telenator. If I understand what you're saying, it depends entirely on whether you're radiusing the soundboard or not...

I think most "flattops" are actually radiused anyway (slightly "domed"), and 30' radius sounds about right... Radiusing the braces is what you'd probably want to do (for cross braces that is).

 

[Telenator]

Thanks Chazmo. From what I've been reading, the gluing surface of the braces get a 30ft radius and then the top is put into a bowl with a 30ft radius formed in it. The braces are then glued to the top and pressed into the 30ft radius form. When it's dry, the top easily holds the shape.

I'm thinking I could mount a post in my radial arm saw so I could rotate a 24" diameter piece of MDF under the blade. As I drop the blade lower and draw it towards the outside of the circle, I can check the radius with a metal gauge. (I would made the gauge ahead of time using a strip of steel or aluminum.

 

[chazmo]

Sounds right, telenator! I guess what I don't know is what the actual top radius is... my only point (which is probably obvious) is that the radius of the braces should match the radius you are trying to achieve on the soundboard. If you go straight or too tight with the radius you would stress the top in a way that could potentially be a problem down the road or might somehow interfere with the resonance of it.

Just thinking out loud. I've never done any of this stuff myself before so take my words for what they're worth as only a "back seat" repairman.

 

[Telenator]

Well this is my first acoustic re-top. Never did one before. I've been building electric guitars since 1981 but have never tackled an acoustic. Should be fun.

 

[chazmo]

Best wishes!

Edit: by the by, this thread might do better in the "tech shop" forum here, telenator!