Bracing Design Question

[Diane Kauffmds]

I've decided that the top of my project guitar is too damaged to repair.. I'm replacing it with a spruce top.. The old top was ladder braced. The instrument is 94% of the size of a 00 size guitar.. I'd like to switch to X bracing, using a Gibson 00 Size plan I found on the internet, which I've resized proportionally to fit the guitar..

1. Given the size of the guitar, would X bracing stiffen the top too much? I figured the ladder bracing was used as a cost saving measure by Silvertone.

2. The Soundhole on the Gibson plan is ~ 1/2" higher than the hole in the Silvertone top.. How does the location of the Soundhole affect sound?.

3. Since the top is 94% of plan size, do I resize the braces too? ie. If the brace plan calls for 10mm thickness, do I make the braces 9.4mm thick?

Thank you

[tippie53]

first off , the bracing would need to be laid out per scale length , sizing down may not work. You start with the scale length and here is what I would do to lay out the braces.
You know where the nut is going to fall and you measure from that point on to the top to the point of where the scale length would fall. Make a mark at that point and draw a 1 in by 6 in rectangle. This represents the apx location of the bridge body.
Gibson and Martin braces are shaped differently but laid out pretty similar. If you are going to keep this as a classical you would want to use a 1/4 in brace . I also would make them about 1/2 in high just a tad lower than steel string. I would use a 95 to 98 degree angle on the main X brace.
so you now plot the X braces to catch the rear of the corner of the bridge rectangle. This will give you structure. The finger braces I would plot so the first one from the intersection will catch the front corner of the rectangle and the 2nd one 1/2 the distance from the first finger brace to the rim.
You can plot the lower tone braces as you wish per you diagram, that should work for you. The upper transverse brace you want about 1/2 in from the sound hole. I would recommend a 3/8 wide by 3/4 brace as this would have less mass ( .2812 sq in) minus the shape you carve it over the 1/2 in by 5/8 in ( .3125) sq in cross section. In fact the thinner brace is actually stiffer than the wider one. Lets face it , getting rid of mass for stiffness is a good thing . Then the lower tone bar , you may X or parallel them and these you may scallop.
Your bridge plate won't need to be as large as a steel string and your top can be thinner.

sound hole location should be in relation to the fretboard. I like to have the fretboard be about 1/8 short of the sound hole. Classical's often radius the board to the hole. I don't think hole location has as much to to with tone as the diameter will. The smaller the hole the better the bass response.



hope this helps

[Diane Kauffmds]

first off , the bracing would need to be laid out per scale length , sizing down may not work. You start with the scale length and here is what I would do to lay out the braces.
You know where the nut is going to fall and you measure from that point on to the top to the point of where the scale length would fall. Make a mark at that point and draw a 1 in by 6 in rectangle. This represents the apx location of the bridge body.
Gibson and Martin braces are shaped differently but laid out pretty similar. If you are going to keep this as a classical you would want to use a 1/4 in brace . I also would make them about 1/2 in high just a tad lower than steel string. I would use a 95 to 98 degree angle on the main X brace.
so you now plot the X braces to catch the rear of the corner of the bridge rectangle. This will give you structure. The finger braces I would plot so the first one from the intersection will catch the front corner of the rectangle and the 2nd one 1/2 the distance from the first finger brace to the rim.
You can plot the lower tone braces as you wish per you diagram, that should work for you. The upper transverse brace you want about 1/2 in from the sound hole. I would recommend a 3/8 wide by 3/4 brace as this would have less mass ( .2812 sq in) minus the shape you carve it over the 1/2 in by 5/8 in ( .3125) sq in cross section. In fact the thinner brace is actually stiffer than the wider one. Lets face it , getting rid of mass for stiffness is a good thing . Then the lower tone bar , you may X or parallel them and these you may scallop.
Your bridge plate won't need to be as large as a steel string and your top can be thinner.

sound hole location should be in relation to the fretboard. I like to have the fretboard be about 1/8 short of the sound hole. Classical's often radius the board to the hole. I don't think hole location has as much to to with tone as the diameter will. The smaller the hole the better the bass response.



hope this helps

Thank you John, it helps tremendously. This guitar is a steel string guitar. I should have mentioned that in my original post. It doesn't have an adjustable truss rod, but has a steel rod in the neck that's really hefty. So I'll be bracing it for light weight steel strings.

[tippie53]

the only thing I would do different is the bracing would be 9/16 hi at the interestion. A 1 1/2 bridge plate and you should be ok. What size is the body? 12 or 14 fret?

[Diane Kauffmds]

the only thing I would do different is the bracing would be 9/16 hi at the interestion. A 1 1/2 bridge plate and you should be ok. What size is the body? 12 or 14 fret?

The body is a 12 fret, 22 5/8" scale length.

Box length = 17 25/32"
upper bout = 9 17/32
lower bout = 13 1/8"

[tippie53]

you will be fine

[Diane Kauffmds]

Thank you again John.