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I haven't done anything quite like this before, but I want to repair the old 1/2 size guitar I've had since I was a kid. It's a made-in-Taiwan "Marquis by Harmony" so it's not terribly valuable, except in sentiment, and the top needs a bit of rebracing as its sunk around the bridge. There's no binding to remove. As I understand the process I apply heat (household iron?) to the back, and try to work a thin metal blade into the joint, and gradually go around and pry it apart. Any hints or suggestions for the process would be appreciated.

A household iron will melt any finish where it is applied. If the guitar is old the glue may be sufficiently dried and "crunchy" that you don't really need heat. I remove backs with single edged razor blades tapped into the joint. You might need a putty knife when you get to the tail and head blocks.

Hot blades and putty knives make it easier too. Pot of hot water.....

This guitar probably dates to the late 70s/early 80s. I'm not sure how much one can infer about the adhesives and finish used. The squeezeout I can see is brownish, and doesn't seem particularly brittle or fragile. It's certainly held together quite tenaciously, and doesn't seem to have failed anywhere on the instrument. Maybe gentle heat gun application with the hot-water-heated blades would be a good choice. I might well have to hammer a blade into the edge to get it started.

I used hot putty knives for years but then had an epiphany that they really don't do what is advertised. The knife cannot apply heat to the sealed joint until the knife is inside the joint. And at that point the joint is open and the heat is useless. In reality, what is opening the joint is the wedging action of the putty knife a short distance away. And this type of joint breakage is a bit uncontrolled. Sometimes the glue joint will give way but the wood can crack and splinter if that is the weaker point.

My razor blade technique allows me better control of where the joint will release.

Do you just keep working the razor blade sideways-ish through the joint? Tap it in at an angle, wiggle it out, tap it back in, etc...?

Yep, pretty much. Just place the blade right on the joint and tap it in. Pull it out and move over the next section. It goes pretty quick. Try to angle the blade so it follows the joint instead of diving into the back or the kerfing.

There are a few places to be careful. When you get to a back brace, don't go very deep or you will separate the brace from the back. When you get to the tail or head block then switch to the putty knife. The blocks might benefit from a little application of heat from a heat gun but be careful not to burn or bubble the finish.

If there is no binding you will probably find that you can get it off just with a hot putty knife. But you can make the knife quite hot. I don’t use a heat gun on the guitar, but I do use a heat gun on the putty knife (more effective than boiling water), and then plunge it into that glue joint.

Success!

What do you think you will do for the top bracing?

I was eager to post the pics, so here's a couple thoughts on the process. A heat gun, pallette knives, and razor blades worked pretty well. The razor blade wanted to wander through the wood (see the tail block) rather than follow the joint if I didn't have enough heat on the glue. The neck block was the last part I did, and that came out nicely.

For the top, I've got two ideas. Either I replace the two fan-esque braces with something much more substantial, or else I just add another ladder brace just above the bridge location. Anyone with more experience want to make a recommendation? I also think I may need to do something to get the curve out before rebracing. I might just try clamping it flat with some cauls and see if it starts to straighten out.

Any recommendations on whether it'd be worthwhile to ditch the original trapeze/bridge in favor of a standard pin bridge? It's a flat top guitar, and even with the top fixed it wouldn't have a lot of break angle over the bridge.

So the simplest option is probably to add a ladder brace, and I'd probably add a pair of vertical braces at the soundhole to help level off that part of the body. The neck side of the soundhole dips a bit from string tension pulling the neck up. But I'm really tempted to just add two long braces running neck to tail, since that'll provide the most bending resistance for the top with the tailpiece and bridge. Any feedback?

There is a reason that 99% of guitars have an X-brace. It works.

Got the neck off. Would've been easier if I could have guessed it was doweled.

Consider carefully removing that patch of wood left on the tail block and affixing it back into place. This would be a good place to use your iron on a very low setting to loosen the glue. You could retrofit a regulation x-bracing pattern onto your top using tone bars. Very nice job BTW...

_________________
Measure Twice,

Karl Borum

She lives! I filled the dowel holes and installed threaded inserts to bolt on the neck. Carved away some of the excess meat on the neck heel and did sandpaper pulls to smooth it out. The neck angle is right on the money. The action is good with room for future adjustment, and there's much more break angle over the saddle. I need to get some black paint and do touchups here and there.

Just now checking into the site after a long absence. Congrats on this project.

Good job Jim!!! It lives indeed.