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Joe Beaver asked:
"So.... if you were to make a large body guitar, say 16+", how would you handle the lower bout bracing?"

I make a lot of 16" ad 17" guitars, and do them the same way: tucking the ends of the UTB and main X, and not the lower X (or tone bars and finger braces, for you folks using more normal brace patterns). All the braces that don't tuck in get shaved away to nothing, and not too sharply either: I think they need to be flexible for some distance back from the end.

As far as I'm concerned, 'tucking' brace ends and using tentellones/brackets to support them is a wash. The important thing is that the ends are supported.

Back when I did repairs I had to replace the UTBs in a few old Gibsons. They used to use a drum sander to take the ends of all the top braces down to nothing. They had a little height where they crossed the liners inside, though. They used spruce for both the liners and braces, and rather than cut pockets they would simply rely on the brace ends to squash the liner a bit when the top was clamped down. Sometimes, though, the brace stock was softer than the liners, and it was the brace end that got squashed. In that case the brace end was not flexile enough to move with the top, and the steady down load on the UTB would eventually start it peeling loose. The owner would bring it in when the neck was up enough to make the action unplayable. Sometimes the brace would simply be gone: they saw the 'stick' rattling around inside and threw it out. I'd cut away the liners where the brace ends would go, fit a new UTB, and, when that was in place, epoxy in brackets to support it at each end.

Keep the loads in mind: the brace ends above the bridge see a down load, and below it they are 'up' loaded. The lower arms of the X only need support if the top takes a hit nearby. It's not supposed to happen, but...

A friend of mine who uses the same Chladni testing method I do shaves the lower ends of his main X down to nothing. He gets pretty much the same patterns I do and his guitars sound similar.

bionta asked:
" ...do you take the same approach for archtops? I've seen and heard your L5 archtop and I still dream about the sound of that guitar. It's a great one"

Archtops are another beast, and draw on violin practice. That one (which did turn out well!) has 'parallel' bracing: actually two bars that run at a bit of an angle along the length of the box, but I treat the ends of 'X' braces the same. 'Parallel' bars are spaced so that they run under the ends of the bridge at that location, and are further apart at the bottom end than the top. Again, look at the bass bar in a violin, and just use two of those (and no sound post). The braces stop a few inches from each end of the top, and although they taper down in height they are not really all that low at the ends; maybe 3/16" tall or so. The ends are beveled off rather than being cut square. There is some stress in the glue line at the end of the braces, and sometimes you'll see a bass bar or top brace on an archtop that has come loose at the end. Keep in mind that violin tops are made to be removable, so that sort of thing is (relatively) easier to correct than it would be on a flat top guitar. Archop guitars pose more of a problem in that regard. On my instruments the bottom surface of the binding is at the level of the top joint to the liners, so you could get a knife in to remove the top without doing too much violence. It's not as obvious as it is on a violin, though, since they use an overhang on the top and back. I will say this is a rare problem on archtops: I have not seen or heard of more than a couple, and never have had the problem on one of mine (knock wood!). Use a new batch of strong hide glue to put on the bars, make the ends reasonably flexible consistent with getting the 'tap tones'/Chladni patterns right, and pray.

arie:
Interesting. I have had guitars where the back tap tones ended up lower than the top, but I normally try to have them be about the same when the box is first assembled. Then when the binding and bridge are on, and the thing is strung up, the back will usually end up a bit higher then the top; perhaps a semitone to a tone. From what I've seen the tops tend to 'play down' just a bit over time. If you start with the top a little higher than the back it could end up being very close in pitch, which invites some nasty 'wolf' notes. Aside from sounding better (IMO) having the top tap tones a little lower than the back is safer (again, IMO).

I've read this several times and just don't understand it. Why go through the trouble of inletting the linings just to cut them off short? You could just as easily draw a line where the X meets the linings, cut it off and taper it could you not?

Because of this: "This allows one to have the advantage of the indexing by the little stubs and still taper the ends of the lower X to nothing." It's certainly not necessary to have that indexing function, but it would be nice. I'm going to do it on the current guitar and see if I like doing it that way.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Jay,

It is an interesting idea. I have had problems with the top turning slightly (enough to pull the center line off noticeably) during glue up. This would have been an easy fix. Since I'm not quite smart enough to think it up, I went with a locator pin arrangement.

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Joe Beaver
Maker of Sawdust

I used Tom West's method for no-tuck brace ends today. It's not hard to do and it gives good solid registration of the top on the sides.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

That's pretty dang clean there, Jay!

So its indexing but having a looser top, is that right?

That's right.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

That sure is pretty to look at, nice joinery there. I still don't think it's difficult to center the top though

I do like how that is still essentially 'tucked ' in too. Like I mentioned before when I do feather the lower X to zero I still allow the lining to go right over the paper thin edge so that it is still kind of sort of tucked in which I believe will help in the event that the guitar top takes a blow.

I'm with Haans, pretty nice work there Jay

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Joe Beaver
Maker of Sawdust

Yea, I agree it's not hard to center the top, but I do like how this locks it in place. No possibility of mis-positioning or slippage while gluing the top to the sides. And, as you said, the brace end is still essentially tucked even though it's tapered down to very little.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

I thought I would add a note to this old thread from a little over a year ago. Today, I fit the top of the current guitar I'm building to the sides. My procedure is to carve the ends of the lower x-brace arms as described above after all the other brace carving is done and after the top is fitted to the sides. I realized I could measure just how much of an effect carving the x-brace ends down has on top stiffness so I did a final deflection test after I was done carving the ends.

Top deflection
0.029" = Uncarved braces
0.037" = All braces carved with x-brace scallops 10/32" tall
0.049" = All braces carved, x-brace scallop heights further reduced to 9/32" tall
0.058" = All braces carved + ends of lower x-brace arms carved

It looks like carving the x-brace ends down had a pretty significant effect on loosening up the top. I can't say whether it's bad, good, or indifferent with regard to how the guitar will sound, but I aim to string it up by the end of next month and I'll see then.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Very nice. Is that a cedar top or maybe redwood???
Ed


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What size/model is that topintended for?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Ed - The top is sinker redwood.

Colin - The top is for a body design I came up with. The lower bout is 15", the body length is 20", and the body depth at the tail is 4 3/4".

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Lower... I don’t give a tuck [GRINNING FACE WITH SMILING EYES]


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My x-brace ends were all tucked up before I adopted this approach.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Tom West's method and Jay's explanation of it has inspired me to try something on my next instrument. Rather than tucking the ends of the lower braces I will interrupt the linings and glue small blocks to the top and back (but not to the sides) at those locations when test fitting the plates. Then I can use those to align the top and back which should eliminate any "slippage" during gluing.