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How important is the fit? I never get this very good and I wonder if it matters as long as the braces are glued well with modern glue that doesn't break down over time.

I ask because after cutting the openings for the top upper bout braces, I'll need to add shims to get a tight fit or add epoxy in those joints.

It's good to talk things out, it just gave me the idea to build up the brace ends and make them fit perfectly. I can do this.

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Hutch

Get the heck off the couch and go build a guitar!!!!

Richard the fit is not critical although you should try to have things in contact. For some braces like my back braces I feathered them to nearly nothing maybe .005ish and then tucked them with no inletting to cut.

Please no epoxy and epoxy should never be used inside the box where access and visuals are limited. Epoxy although we can get most to release with heat it's not nearly as friendly as Titebond Original or HHG in terms of being serviceable. Only serviceable glues that release with heat and no one having to jump through their sphincter to get things to release are suitable for inside the box. I would make the same argument for outside the box too knowing many here use epoxy for fretboards and I did too until I changed back.

Even when the fit is not great when we install the top the squeeze out usually fills voids and you are good to go.

Regarding your statement about modern glue that doesn't break down HHG takes a century or more to to start to break down unless it's in extreme conditions and no one I know of or know has ever avoided it thinking that it breaks down in time.

EDIT: Had a thought as I was leaving this thread about "modern glues." The case could be made that we have no idea what modern glues will do either 100 years out when they have not been around that long. Data matters.

Every day, in every guitar repair shop on the planet, guitars arrive for repair of loose braces. In the vast majority of cases, the braces were once glued with these modern glues of which you speak.

Modern glues absolutely do break down, become brittle over time, let go in excessive heat and humidity or due to a physical shock or as the body of the guitar changes shape over time etc.

Well that makes my life easier, thank you.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

Then why don't we tuck all the braces instead of just the ones in the upper bout on the top?

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Hutch

Get the heck off the couch and go build a guitar!!!!

Some builders tuck all braces. Some don’t. I wasn’t really commenting on the tucking of braces, just noting that modern glues are not impervious to failure.

Side note: tucking a brace does not confer invincibility upon it, consider the prevalence of loose back braces, which are tucked more often than not.

And how can that be avoided? Would gluing both surfaces make a difference? I only put glue on the braces but they are set in place so fast that I feel the other surface is getting plenty of fresh glue.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

Something to also consider is how you will install binding, specifically which glue. I try to get the brace pocket, especially on the back where it will be visible through the sound hole, to be as tight as possible. There is the aspect of good workmanship, but there is also a function if you plan to use CA to glue in binding. Having gaps in the pocket can give a pathway for the CA to run down the side on the inside. It’s then a pain to sand out.



Brad


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That's a real tight joint you have there.

My biggest problem is marking the slots for them. The mold is in the way. Holy cow, I just thought of a good way to do it, it always helps to talk like this. I was thinking transfer paper stuck to the braces. I don't know how you guys do it but I'm all ears.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

Just make sure your joints fit well, use quality glue, and get the clamps on in time. Beyond that, how the guitar is cared for during its life is an important factor and one that you may not have control over if you’ve sold or gifted it to someone.

I use the plexiglass back template to mark them out, cut with a router and 1/8” bit to get the pocket close and then finish it off with a safe edge file.



How I used to do it, which also works, is the Robbie O’Brien method he teaches in his course. He clamps the plate onto the sides while they are in the mold. The sides are sticking above the mold about 1” or so. He puts a bit of masking tape on the side where the brace is coming out, marks each edge of the brace, and then cut / file as needed. It takes time and is fiddly (IMO) but works well.


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Thank you. I think I would like to get some good templates like that.

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Hutch

Get the heck off the couch and go build a guitar!!!!

This method works pretty well http://www.luthiersforum.com/forum/viewtopic.php?p=624583#p624583

That's brilliant! Too late for this guitar but the next one, I'll give this a try.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

But this from Hesh "For some braces like my back braces I feathered them to nearly nothing maybe .005ish and then tucked them with no inletting to cut.". I like that.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

I "tuck" the braces in the upper bout. This is where I think the tension of the strings is pushing the top down and creating the need for the most support. I generally don't "tuck" the lower legs of the X brace or the tone bars in the lower bout, but gradually taper the ends to nothing. I like having a "looser" perimeter in the lower bout and will sometimes even perimeter sand a bit if I don't think it is flexible enough. Taylor routs a groove around the lower bout to loosen things up, but I think that creates a "stress riser" and is a bad idea. We all have our opinions and way of doing things, and many different ways can work.

An even greater source of stress than string tension is humidity. If the back has gone concave, the braces are being pulled with enough force to bend them, and the ends will try their hardest to get loose and spring back straight. Diagonal braces have effectively larger glue area for this since the wood only shrinks in one direction. Feathering them out makes the ends very flexible so they can't concentrate enough stress in one place to break the glue. Although depending on how steep the slope is, the brace itself could split instead.

If you put pressure on the outside of the plate over the brace it's trying to peel the end of the brace loose if it can. Most glues, modern or old, don't have a lot of peel resistance, so once they start they keep peeling up. Thinning the brace down so that it's flexible enough to move with the plate limits the stress riser there, but keep in mind that most woods are far stiffer along the grain than across it. You have to get them pretty low to eliminate the peeling risk.

So long as the end of the brace can't move away from the plate it should not peel up, so the fit that counts is the top of the brace touching the bottom of the pocket. Gaps along the sides are a cosmetic issue, but don't hurt otherwise. Obviously, the liner (or whatever) has to be glued to the side well enough to keep the brace end from moving.

Gibson used to use the nose of a belt sander to feather the brace ends down to nothing at the very edge of the plate. It would have a little height at the inside edge of the liner, but rather than cut inlets they seem to have just hogged down the clamps to mash down the liners. The problem was that they were using spruce for both the braces and the liners, and sometimes the wood in liner was harder than the brace, so it was the brace end that got mashed down. With the brace effectively broken at the end where it hit the liner it would peel up. Those came into the shop a few times back when I did repairs. There was a stick rattling round inside the guitar, which the guy tossed out, and now the neck is pulling up, so you replace the UTB. I did like epoxy for the brackets.

Since bridge torque basically produces a down load on every brace end between the bridge and the sound hole I inlet all of those. Below the bridge the static load is pushing the brace end into the top, but you still have to worry about what happens when somebody sits on it, or pushes a carry-on bag up too tightly. The neck load is mostly on the UTB, but it's heavy, so I keep those ends tall so they're less likely to split.