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Thanks for the clarification, Woodie.

What I like best about this is all I need to change is make the UTB 60’ and foregoing flattening the rims. I’m already doing the rest of it so, win-win! Thanks again.


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This is definitely nothing more than a water cooler discussion for me because (1) most importantly, it’s tested, easy to execute, and works; (2) I would never in my wildest dreams, even if my house were on fire, debate anything remotely engineering related with Woodie and the Greenridge Gang unless it were profoundly obvious; and (3) I just really appreciate that you guys share these things… But wouldn’t the long-grain stiffness of the big, beefy UTB (even where tapered down at the ends) win against the cross-grain stiffness of the top every time?


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FWIW, I glue all top braces at 28’ including the UTB, glue it to flat rims, and get the geometry I like with the amount of fall way I like.

While comfortable with some of the math and a bit of the physics, engineering competency is best attributed to the other Greenridge denizens - but thanks for the thought. I suspect that the impact of the flat caul is quite incremental, and as Mr. Bond reported, is not needed to generate his desired neck-body geometry.

Thought experiments were common at Greenridge, and the one I recall related to this discussion sought to illustrate the incremental effects of material removal from braces or other guitar structures for operations such as voicing/revoicing.

- If one were to take two rectangular braces designated as A and B milled from the same billet, radius the corresponding faces, then glue together such that the join line between A and B is straight, the two braces would act as opposing springs to counterbalance any bending force along the joint.

- This balance of opposing spring forces would exist until such time that one or the other of the braces was modified (or RH shifted, shop temp changed, other loads were applied, etc.... but let's ignore that end of it for a bit).

- If we were to progressively shaved material from B on the surface opposite the A-B joint, we would expect the balance of forces to be disrupted such that the A side of our wooden spring structure would begin to dominate and bend the glue line back towards the original A face radius.

This is far easier to see in the real or in sketches, but it raises the question as to just how much material must be removed from B to see our composite A-B spring brace glue line return to that design radius we applied to the two parts of it prior to glue-up. The answer is that it is very probable that however small the amount of glue and material from B remaining on A might be, it would have SOME impact on observed radius of both the joined face and the opposite faces away from the joint.

The point here is that small changes in caul radius should be expected to generate correspondingly small changes in overall geometry, and whether that small change is meaningful to your desired end-state neck-body geometry really depends on your expected outcome.

By the way, I am feeling better (the decongestants finally kicked in), and can actually stay awake through a film. De Palma's Body Double was the guilty pleasure last night, with the film-within-a-film sequence backed by FGTH's Relax the stylistic high point of the movie. De Palma's heyday, and a time when we were all a bit more innocent, somewhat less concerned with consequences, and Hollywood still knew how to produce engaging film in job lots.

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Maybe I’m misunderstanding the situation, but, I think applying the cubed rule of stiffness between a general 3/8 - 1/2”high UTB long grain vs a .100”ish top side grain means the top is taking orders and that’s just that.

Yeah, I don’t think anyone is saying anything different from that. I don’t think we should assign much significance to “springing” the UTB by gluing it with a flat caul versus a 60 foot radius caul. That’s really not the focus (at least, that’s not my focus when I have used this method). The focus is on the fact that the UTB has a flatter (but not completely flat) shape than the rest of the top braces, and that helps create a flatter upper bout, which needs very little sanding to mate up with the bottom of the fingerboard extension.

I’m clearly doing something different than some of you guys and I don’t know what it is. I glue my UTB flat and the other braces on a 28’ radius. But the radius on the rims is enough to put a sort of hump that I had to sand down. I’m going to try sanding the upper area of the rims flat on the next one and see what happens.

What I did and my tutorial indicates was sand my UTB flat (you can put a slight radius in it like Woodie and crew do that's a good idea) and then I flattened the upper bout as per the tutorial. So where you have in the upper bout a 28" radius my rim, above the waist is/was flat. The "flattening the upper bout" in addition to a flat or very slight radius UTB is the whole point of the tutorial. These two things, flat UTB (or slight radius) and the rim flattened face down and jacked-up is the preparation for the fretboard extension to transition onto the guitar top clean and gapless.

Like Hesh said, the tutorial has the details. One thing I would add is, when it says flatten to the waist, it’s the north end of the waist where you want to stop. Or, like Ed recommends, just down to the upper transverse (aka the north end of the sound hole).

If you flatten too far down it will impart more fall away into the board than you want. Ask me how I know.

Brad


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This is the first time I've heard anyone have this issue. I never had this issue either and did this procedure around 50 times. On an acoustic I would like to have 0.015" fall away at the last fret and this got me there nicely.

I can only say what I experienced. Using the tutorial exactly as shown for 00 sized always worked out perfectly. I used the same procedure on two dreds in a row and both ended up with too much fall away.

Could be some other factor, I’m not sure. I like Ed’s suggestion to just flatten to the top of the sound hole. That makes sense to me.


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That's what I'm thinking.

It makes sense that the process would come out differently for some body styles but I did the same thing for dreads, OMs, SJs and L-OOs. But the longer the extension over the body I can see the fall-away being greater since this process only sets an angle not a result. It's got this idea from Frank Finochio who said it came from how Martin back in that day did things.