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  #1  
Old 12-31-2016, 02:32 PM
springer springer is offline
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Default Harmony H1203 rebuild ?

I have an early H1203 excellent rebuild candidate. Top looks in perfect shape no cracks. Neck needs reset and is coming loose. A crack in the upper bout near the neck. I want to change to X bracing, string thru pin bridge, and so on. Never done this sort of thing before and I'm taking my pointers from a company that specializes in Sovereign rebuilds. I have a few questions, such as... what is the best way to remove the back? I've seen one youtube where the guy used a thin Japanese luthier saw and carefully sawed between the back and purfling removing very little material. What about applying heat or does that risk ungluing nearby areas i.e. back braces?
The rebuild company mentioned above like to structure their X brace with 100 degree forward shift. I'm guessing that would mean the angle(s) on vertical axis adjascent to lower and upper bouts are 100 degrees, which would result in the angles facing the sides 80 degrees... would that be correct?
Not quite ready to start this project. Just gathering some info at this stage.
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  #2  
Old 12-31-2016, 06:41 PM
mirwa mirwa is offline
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Removing the back of the guitar can be extremely messy sometimes.

If it has binding, you can use a small router to remove that binding, then using a separation knife slice through the join and work that all the way around.

Sometimes you need heat, sometimes you need steam.

At points where you come upon the neck and tail blocks, you will need more patience

Majority of the time, cosmetic work is required when refitting the back on.

Steve
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Old 01-05-2017, 02:08 PM
springer springer is offline
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Last edited by springer; 01-05-2017 at 03:45 PM.
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Old 01-05-2017, 03:31 PM
springer springer is offline
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Woops! Posted the above reply in the wrong thread. I meant to post this in the "scalloping after the fact" thread regarding my Yairi Alvarez.
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  #5  
Old 01-08-2017, 10:22 PM
M Hayden M Hayden is offline
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If the guitar isn't bound like a lot of Harmony instruments, a palette knife or three, some hot water or steam, and time and patience will get the back off. They use hide glue, and lots of it.....
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Old 01-08-2017, 10:50 PM
Truckjohn Truckjohn is offline
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This sort of work will destroy the back bindings and most likely leave you needing a refinish.

This is a very involved job and honestly - it's probably easier to just go ahead and build your own guitar from scratch.

The ones we see people doing this on most are the ones with no back bindings. They are way easier to do. Then - you just very gently work a thin pallet knife (or razor blade) and alcohol into the glue joint - and crack crack crack - the hide glue comes loose.

Whatever you decide - post some pix.

Thanks
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Old 01-12-2017, 03:32 PM
downtime downtime is offline
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Just curious, who are you consulting on the x-bracing conversion?

I have a Sovereign H1203 that was x-braced by moonlight luthiers.
It had severe bellying and desperately needed a neck reset.

After the conversion the top is flat, action is perfect and the tone is vastly improved.
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  #8  
Old 07-23-2017, 03:38 PM
harmonyrepairs harmonyrepairs is offline
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Default Acoustic guitar back removal

With the right tools and technique, it is no problem at all to remove the back off any acoustic guitar. Problems occur when the back receives an impact on the binding. In most cases, that leaves a weak spot, usually in the side wood. We use a specially set up router to machine away the OEM binding. And we use a sharp new bit on every guitar. When the bit hits a bad spot, a little bit of side wood blows out or chips in some cases. We have worked out techniques to avoid this, but it still happens on 10 percent of the guitars we work on.

A more significant problem is replacing the back. I contend this takes a special guitar body holding jig which supports and straightens the guitar in all directions while the liner blocks and end blocks are re-aligned and straightened. We use the Mega Mold from CNC products for both top and back re-attachment. This tool or jig is fantastic for re-gluing the back or top. I am in no way associated with CNC products. Just a satisfied customer.

A more interesting question is, "What is the best way to remove a neck without steam damage?" We think we have the solution. Any guesses?
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  #9  
Old 07-24-2017, 06:32 PM
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Howard Klepper Howard Klepper is offline
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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 90 a tight X, and 100 or more a loose one. I have gone as open as 102 on a dreadnought body; the mid-1930s Martin dreads are about 99-100. 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!
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Last edited by Howard Klepper; 07-24-2017 at 06:42 PM.
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  #10  
Old 07-25-2017, 08:53 PM
harmonyrepairs harmonyrepairs is offline
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Default Harmony H1260/H1203 back removal

Comments below apply only to Harmony Sovereign guitars made between the late 1950's and 1971.

Hide glue is not used on Harmony H1260/H1203/H1270/H1201/H1250/H1266/H1265 liner blocks, top or back. They used a very brittle adhesive that is distinctively red in color. Never seen anything like it on any other acoustic. Also, sometimes they used PVA to glue the liner blocks to the sides. The red glue, as I call it, is very durable. I have not seen any Harmony guitars where other than red glue was used to adhere top and back to the liner blocks. Using the excellent StewMac seam separation knife the back separates easily except for neck and tail blocks. The back is much harder to separate from neck and tail block glue up. The problem is preventing damage to the back finish and causing cracks. A mini flat spatula cut down to 1-1/2 inch and sharpened to a chisel edge works well on the blocks. At this point I am at 95% success rate on my separations without damaging the sides or back planks at any point. The only exception is when there was a bad impact to any place on the back binding. Usually the back or sides are fractured to the point that breakage happens no matter what technique is used. I must say that success in this area most definately requires lots of practise. Attempting first time back removal on a nice Harmony is a bad idea. Try it on two or three junkers first. Experience is the only way to learn what the materials can handle.

Steam is not going to de-bond the red glue adhering the back to the liner blocks on a Harmony Sovereign. Steam will only damage the surrounding finish and other components. Your goal should be back removal without causing any damage at all to the sides or the back. Same thing applies if removing/replacing the top.

Also, the back binding is not usually worth all the trouble to remove intact with xacto knives and the like. It is so much easier to just rout the stuff away and install new binding after all interior repairs are complete and the back reinstalled. With proper router set up and the correct bit, and careful preparation on the sides (i.e., lots of green tape) you can remove the binding without leaving a mark on the sides or the back. Once binding is removed, splitting off the back is straight forward. My comments only pertain to Harmony Sovereign guitars as other acoustics require or justify different techniques. Regardless, practise on a throw away guitar.

When replacing the binding, remember to sand with 400 grit and clean carefully with high percentage alcohol before glueing. Also, use the binding adhesive recommended by StewMac and lots of 3M "For Hard to Stick Surfaces" green tape to protect adjoining surfaces. Only 3M green tape (and most likely the brown stuff sold by Stewmac) is safe for lacquered surfaces. All other tapes eat lacquer.

Last edited by harmonyrepairs; 07-27-2017 at 04:19 AM.
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