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Cumpiano's Lower Back Braces
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Author:  sdsollod [ Tue Jun 07, 2011 7:51 pm ]
Post subject:  Cumpiano's Lower Back Braces
Cumpiano's book shows that the lower back braces should be 3/4" wide. That seems excessive. pfft I have built 5 guitars and I have not made them that wide. Should I? What width do you guys use for the back braces?
Steve
Author:  theguitarwhisperer [ Wed Jun 08, 2011 12:48 am ]
Post subject:  Re: Cumpiano's Lower Back Braces
Cumpiao imparts a pretty good arch to the back of his guitars. I'm guessing the 3/4 inch footprint imparts some stability against twisting.
Author:  Steve Saville [ Wed Jun 08, 2011 2:05 am ]
Post subject:  Re: Cumpiano's Lower Back Braces
I would never go 3/4". 0.3125" is as wide as I would go.
YMMV
Author:  meddlingfool [ Wed Jun 08, 2011 2:21 am ]
Post subject:  Re: Cumpiano's Lower Back Braces
Ok, non expert opinion here, but here goes..
There seems to be two ideas about backs and how they affect tone. Some folks like a high pitched 'reflective' back, some folks like a lower pitched 'coupled' back that is a half step above the top. I'd guess you could do both with taller bracing, but it's probably easier to get a coupled back (dropped resonant pitch) with wide flat braces as they have more mass, which drops the pitch, and more flexibility, which also drops the pitch. If you look at the Stew Mac dread plans, they are 3/4" wide but only 3/8" tall. FWIW, my Gibson AJ has 3/4" braces on the lower back, and it sounds fine fine fine.
Righto, let's have some dissent!
Author:  Laurent Brondel [ Wed Jun 08, 2011 5:58 am ]
Post subject:  Re: Cumpiano's Lower Back Braces
3/4" is "traditional" width for the two lower back braces, i.e. as found on pre-war Martin guitars until very recently. They are meant to be much lower than the two upper braces, typically 5/16" to 1/2" tall.
As to the effect on tone: more gluing surface but less stiffness, IME that tends to enhance the bass registers. The large gluing surface of 3/4" braces is potentially better at resisting shocks too.
Author:  Bill Hodge [ Wed Jun 08, 2011 8:42 am ]
Post subject:  Re: Cumpiano's Lower Back Braces
Laurent Brondel wrote:
3/4" is "traditional" width for the two lower back braces, i.e. as found on pre-war Martin guitars until very recently. They are meant to be much lower than the two upper braces, typically 5/16" to 1/2" tall.
As to the effect on tone: more gluing surface but less stiffness, IME that tends to enhance the bass registers. The large gluing surface of 3/4" braces is potentially better at resisting shocks too.



Laurent,

I really like the creative aesthetics of the second pic. Superbly done sir! You and certain others on the OLF always challenge and inspire me to a much higher level of visual excellence!
Author:  Laurent Brondel [ Wed Jun 08, 2011 10:10 am ]
Post subject:  Re: Cumpiano's Lower Back Braces
Thank you Bill, the brace and strip hardwood caps have a function, or so I believe.
Author:  jfmckenna [ Wed Jun 08, 2011 10:38 am ]
Post subject:  Re: Cumpiano's Lower Back Braces
I've done it both ways and never could tell a difference in tone.
Author:  Colin North [ Wed Jun 08, 2011 10:55 am ]
Post subject:  Re: Cumpiano's Lower Back Braces
Laurent Brondel wrote:
Thank you Bill, the brace and strip hardwood caps have a function, or so I believe.

Those are both nice Laurent.
Curious - first pic looks like cross grain strip, second looks long grain, but I think it may actually be a lamination over crossgrain to give a consistancy to the bracing scheme - ?
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