Sound Board Bracing

You can see the finished Go-Bar deck.  It took all of a half hour to build.  I cut two pieces of 3/4 MDF slightly larger than my radius dishes, nipped the corners off, drilled holes and enlarged them slightly on the top, then bolted the top and the bottom in place.  I used 5/16 threaded rods.  I could have used larger, and they would have had less wiggle, but the 5/16 are working quite well.  I didn't cut the rods, but left them at the full 36 inches.  The extra length will allow me to raise the upper deck, if I want to use it for projects other than guitars.  (My wife wants me to make some boxes for a variety of tea bags, something well crafted that could be used on the table.) 

The go-bars themselves, I made from poplar.  I had thought about ordering some fiberglass rods from McMaster-Carr, but frankly didn't want to wait.  Poplar is a stringy, hence springy, wood, so I cut some strips at about 1/8th inch thick.  Any thicker and they're too stiff.  At any rate, they work like a champ.

I have an order of precedence in gluing on the braces, and I won't outline it here.  It begins with the X-Bracing.  I begin the process by cutting them from lumber.  I'm cutting the bracing from a redwood 2 by 4 that I rescued from the Home Depot.  The first trick is the grain.  I wanted a piece with tight, even and straight grain.  It doesn't where that grain is on the billet (I'll call it a billet from here on out) but when the brace is cut, the grain should run the length of brace.  Looking at the end grain, it should be vertical to the soundboard.

I cut my X-Braces at 3/8 wide and 3/4 inches high.  They will lose a bit of that dimension when planed and sanded, but it also makes for a stiffer top.  To radius the braces, I do two things.  First, I begin by planing a preliminary radius on the brace.  Take a cut with the plane about one inch from the end, another at an inch and a half, another at two, et cetera, until you reach the center of the brace.  Do the same for the other end, then run a squiggly (technical term) pencil line down the brace.  I finish on the radius dish, as you can see in the photo, by laying sandpaper at the approximate place where the brace would lie on the sound board.  Using light downward pressure, and short strokes, I sand until the pencil lines are gone.  When I have done that, just to be sure, I put another squiggle down the brace, and sand that off as well.  I say "light downward pressure," because you don't want to bend the brace into the radius, you want to sand it into the radius.

I join the X-Brace before I glue them in place.  Layout is important.  The first step is to find the place where bridge will be on the top.  Using the LMI ruler, I measure and mark the bridge location.  I then mark the outside string locations.  The X-Brace should allow for about 1/2 inch on either side of each e string.  You want the pins that hold the strings to pass through the bridge plate, not the bracing.  The joint itself is essentially just a half-lap joint at the angle of the X.  After I have sanded the radius into it, I lay it on the soundboard, put the other brace over it, and mark the angle, then cut it with a razor saw.  I put the other brace over the other, so it covers the razor saw kerf, mark with a sharp x-acto knife, then cut the second kerf to the same depth, about half-way through the brace.   The waste between the kerfs should pop right out with a sharp chisel.


The trick is not to cut it too wide.  Better to cut the channel too narrow and take some shavings to get it to the point where the other brace slips into it snugly.  With the other brace in the channel, I mark it with the knife, cut two kerfs just inside the markings, make the adjustments for fit, and glue them together.   You don't really need to wait for the glue to dry before gluing the brace to the top, and in fact, I didn't.

You can see the go-bar deck in its full glory in the photo at left.  Here the trick is to get the brace in place with the first bar.  With the glue on the braces (and I do use Titebond) they have a tendency to slip around.  Once it is in place, then it is simply a matter of placing the go-bars so you get a nice even line of squeeze out along the entire length of the brace with no gaps.  This shouldn't be a big problem if a proper radius was sanded into the brace.  Although you can't really see it in the photo, I do have a sheet of poster board between the soundboard and the dish.  Although it isn't a big deal right now, eventually, when it comes time to adjust the kerfing on the sides, I will cover the dish with sandpaper, and so I thought I would get in the habit of protecting the show face of the sound board right from the start.

Before I glued in the bridge plate, I did scallop the X-Bracing.  The scallops on the ends of the braces start at about 1 and 1/2 inches from the sides of the guitar.  The secondary scallops are positioned so they line up with the bridge plate.

Cutting a scallop takes a little practice, but not much.  Start with the sharp chisel.  (Mine this morning were a bit dull, so I will need to attend to it.)   For the end scallops, start at about 1/2 inch back from the end.  With the back side of the chisel up, cut on either side of the brace to create a peak, then chisel then scoop the peak away.  Go back a bit on the brace, and repeat the process, cut away the sides until you have a peak, then scoop the peak away.  For the secondary scallops, at the center of the scallop, cut a kerf to the depth of the scallop.  Then do as above, just working from the center kerf to the mark.   

The next step is the bridge plate.  It is made from a block of (I think its cocobolo) that I found in the garage many years ago when we were living in Michigan. It is a beautiful piece of dense wood, and this is the first cut made into it.  I had in mind that someday, when the spirit moves me, I will make a morris style plane with the remainder of the block, but for the moment, I will let it serve as a bridge plate.  It is about 1/8th inch thick, and positioning is important.  Although I plan to make a pinless bridge, the bridge plate should be below the bridge and the pins should pass through it (not the braces!).    You can see the shaping from the photos, and the reason for the particular shape will be obvious when I install the next set of braces.