X brace shape
 

Hello Forum.
Can anyone please tell me if it is usual to radius the bottom of X braces, or just leave them straight when gluing/clamping to soundboard?

David Miles.

“Radius the bottom “ of X braces? Never heard of anyone doing that and it would defeat the glue joint. If you meant the top side of the X brace then yes, many builders do radius them but not all.

If you want a radiused top the X-brace should be radiused on the bottom. Many guitars are braced that way, often with a 28' radius, and some aren't and are built flat.

For an arched top, I would think you'd want all the braces (except the top brace under the fretboard) to be sanded on the bottom to match the top radius.

Frequently, yes. Some more traditional designs are actually flat...

but, many "flattop" guitars have both a slightly radiused top and back, the x braces and whatever back braces are being used are sanded to the proper radius and then the top/back glued to them to create a slight arch.

I feel like an idiot for my reply. I thought you were talking about radius on the profile cross section. Sorry.

X brace profile
 

Thanks everyone for your speedy reply's

David Miles ( UK )

The overall amount of arch in the top is only one factor that affects the timber of the top. The flatter the brace generally results in a lower frequency response and the higher the arch will generally increase the frequency of the top. Other factors are in play and the brace archings aren’t the final authority but only one factor in the mix to be considered.

Research “bowed musical saw” playing and this may shed some additional light on your question.

Something about the way it was worded had me thinking the same thing though :)