[Howard Klepper]

You are being a bit ambitious for someone who has no experience working on guitars. If you are not experience in other wood working, you probably shouldn't. But if you are set on it:

There is no need to rout away the binding on a Harmony. It will peel off easily once you get it started with a scalpel or ExActo knife. Lift up and out at the same time. The lacquer is usually not so thick that it requires scoring, and the 50+ year old hide glue is pretty weak. If you rout the back off (i.e., go further than the binding rabbet and rout to the inside of the liners), you will no longer have a usable back.

I like to separate the back from the liners and side cold and dry, with a knife (not a sharp knife. People vary on their choice of tool, but I find a palette knife to be usually too small and thin, and a putty knife too stiff and thick. Some sandwich spreaders or cake frosting knifes are about right). You push and rock into the glue line a way that is hard to describe, and takes some practice. But the good news is that often the old hide glue comes apart very easily. Heat can help a lot, but it also can mess up the finish and make the liners detach from the sides.

Forward and rearward X placement is not described in degrees. The X angle is. I suggest reading my article in American Lutherie #125 on how to design and locate an X brace. I wrote it in response to a reader's question. I'm attaching it below. But there is a lot it doesn't tell you about the rest of the top bracing and the mechanics of gluing braces that you will need to pick up in other places.

This is an excellent question that gets to the heart of steel-string acoustic design. And congratulations on taking the next step as a builder by designing your own bracing plan.

Your instincts about this are good, too--you have focused on the things that matter when locating the arms of the X brace. You did not ask, as many people do, "How far should the X be from the soundhole." That is not a significant design parameter; I do not measure it when designing bracing for a new body. It's just an artifact determined by the design decisions that do matter.

Once you have drawn the body perimeter (the "plantilla" to classical builders), the next thing to do (as you already have done) is to choose the scale and locate your bridge outline within the drawing. It's also a good idea to locate the end of the fretboard and draw the soundhole on your plan at this point. Then you make your first major decision: where you want the lower arms of the X to cross the bridge wings. This decision will have a significant effect on the sound of the guitar.

In the "forward" X plan used by Martin in the mid-1930s, the lower edge of the X arms intersected with the lower corners of the bridge wings, so the brace arms did not fall under the bottom edge of the bridge. They were immediately outside it, under the lowermost part of the short sides of the bridge. This position allows for strong bridge movement in the lowest vibration mode of the top--the one in which the whole belly of the guitar pumps air (called the 0,0 or monopole mode). The result (along with brace scalloping) is the powerful bass and baritone range output of these guitars.

The "rearward" change that came at the end of the 1930s put the lower arms of the X a short way (about 1/2") inside of the lower bridge corners. This inhibits the bridge movement in the monopole mode, resulting in the greater midrange bias of the sound heard in guitars from that period. Many people favor that tonal balance. In general, there is no free lunch in guitar design. Strengthening the bass is likely to cost you something in the midrange and treble. The Martins from the 1940s also were better able to resist the pull of the strings, and the tops from these years generally belly up less. In the 1950s, Martin moved the X arms to a compromise position. The upper edge of the X arms intersected the lower corners of the bridge. But this has varied over the years and with different models.

There have also been some guitars that have the X arms higher up on the bridge. On the Gibson Advanced Jumbo, they touch the upper corners of the bridge wings. I think of this as a "hot rod" design--one that sacrifices some stability and potential longevity for greater performance (if a big bass is the performance you are after). If you should choose such a design, it is critical for the bridge plate to back up the lower bridge corners, or they will pull too sharply on the top.

So, you have decided which kind of sound you want to go for by choosing the point where the X arms cross the bridge, and how much risk you are willing to take of excessive top bellying (the gauge of strings to be used will be another factor in making this choice). The next choice is how open an angle you want between the X arms. Since you have fixed the location where the X arms cross the bridge, you will alter the X angle by your choice of where to anchor the upper ends of the X. Putting them closer to the upper transverse brace will close the angle; putting them closer to the waist will open it. Once again, the choice is about tonal balance, and tradeoffs between stronger bass and greater longevity. The uppermost anchor point for a narrow X angle will be when the X arms meet the sides immediately below the ends of the upper transverse brace (but it is possible on a 12-fret guitar with a long fretboard--say, 21 frets--to put the X too close to the soundhole or even under it if you anchor the X that high up. That's why you located the end of the fretboard and drew the soundhole before designing the X). The lower limit for anchoring the upper ends of the X is a little bit above the waist. Just how much above the middle of the waist will depend on how the waist curves into the upper bout. The X should anchor above the point where the waist curve straightens out, so that the force on the X gets transferred to the sides where they are able to resist it without being pushed outward.

If you would like degree numbers for the X angle, I would call 90º a tight X, and 100º or more a loose one. I have gone as open as 102º on a dreadnought body; the mid-1930s Martin dreads are about 99-100º. There is a great online resource for bracing information on the Unofficial Martin Guitar Forum. Look in their Technical Forum, right at the top, for the Martin Bracing Library. Despite its name, there is information there for Gibson designs as well.

Happy building!