1920 Gibson "A" Mandolin
Shoring up a Sagging Top
© Frank Ford 2007; Photos by FF

	Here's a sight nobody likes to see! It's a fine old Gibson mandolin whose top has slowly collapsed under the load of string tension pressing downward on the bridge. Somewhat wider grain and a thin spot in that area have obviously contributed to the problem.
	I made this little tool just for reaching in the soundhole of this style mandolin and jacking the top back to its original position.
	Here's an exploded view of the tool.
	After swabbing the inside of the top with a rag satruated in hot water, I cranked the jack to restore the top to its correct form. I left the jack in place for a week, and after I took it out the top remained in good shape.
	I taped a pen to my dividers and traced the contour of the top on a piece of 3/4" thick plywood as a first step in plotting the interior shape so I could make a brace to fit. Because the top had a somewhat springy feel on the treble side, I decided to make my brace long enough to span the entire width of the top.
	Using the Hacklinger magnetic gauge, I measured the thickness of the top at intervals across where I'd be placing a reinforcement brace.
	Transferring the measurements to my traced contour line, I was able to make a pretty fair estimation of the exact interior contour. The arrows point to the thin spot where the bass side of the top had failed.
	I wanted my new brace to be strong yet flexible and light, so I split some spruce to get the straightest grain alignment with no runout. That would ensure a brace that couldn't split under any load.
	A laminated brace would allow me to establish the contour while keeping the grain alignment so I'd be able to make a strong brace that wouldn't be overly stiff. I worked the spruce down to just about 1/32" thick strips.
	Once I'd trimmed my plywood form, I laminated layers of the thin spruce.
	Here's my "glue-lam" cut to length and ready for installation. The idea was to have the brace strong, flexible and very light so it would have as little tonal influence as possible.
	Getting a glue covered brace lined up inside is a difficult enough prospect when working through the soundhole of a guitar, let alone such a small hole as on this mandolin. I glued a pair of magnets onto the back side of the brace to help me with the job.
	Because the brace was thin and springy, and contoured through its length, I was able to feed it into the instrument.
	Then, with two matching magnets on the outside, I gently lifted the brace toward the top, and it snapped right into position.
	A few strips of veneer protected the top as I clamped the brace.
	Viola! (OK, not "viola" but "mandolin") No sign of the old sagging problem, even with full tension (.011 - .040) strings.

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