Official Luthiers Forum!

Howard, your input is much appreciated. I will continue to evaluate my design and take your input into serious consideration.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Lots of points to address here; let's see how many of them I can remember.

Mass:

As has been pointed out, ALL of the bracing on a top weighs something like 30-40 grams, and ten or so for a normal UTB sounds about right. The top itself weighs something like 120-150 grams, so if you're looking to save weight, that's the place to look. Weight is not the most important thing, of course.

I always feel some repair experience is a real help in thinking this sort of thing through. Splitting of the top at the sides of the fingerboard is a very common problem. In part I think it's because the ebony just never stops shrinking. At any rate, in a standard design, once the top splits you're relying on the strength of the glue lines between the various braces between the top edge and the hole to keep the neck from shifting inward. Sides don't do much here. That's what the 'popsicle stick' is about: it's an effort to get a lot of glue area to keep the top from shifting. If you use HHG for all of the bracing you might not be in bad shape: things won't move until the glue line actually fails. With the modern glues you have to deal with cold creep, and they will all move eventually. In that case you're stuck with hoping that the small area of top wood in shear along either edge of the 'board will hold, and in the long run, it won't.

Using a 'chin' extension on the neck block gives you a lot of gluing surface. If you make the block wider than the fingerboard there is good support to help keep the top from splitting there. I like to make the block about 1/4"-3/8" wider at the neck end than at the fingerboard end; the taper of the edges prevents concentrating the stress along a single grain line.

This can still shift inward if the neck recieves a blow on the back. You can do what Taylor does, and make certain that the neck block extension actually makes contact with the UTB, but I don't trust that. You only have to miss by 1/32" and the neck can shift, as it did on a dropped 12-string I made some years ago, splitting the top along the fingerboard edges.

To get around this problem I've been using an 'A' brace system. The braces are about 1/4" square, and run from inlets in the neck block extension, through the UTB, and into shallow inlets in the upper arms of the X braces. This has proved to be extremely stable, and strong enough to withstand hard knocks to the back of the neck. You could, of course, use a 'flying' brace system for this, with or without CF, runnig to the sides at the waist. The important thing is that these braces are substantially in compression (avoid shear loads) and tightly tied in at both ends.

With this system I've gone to using an UTB that's only 1/4" or so wide on most of my guitars, by, maybe, 5/8" or so tall.

I realize that this is a 'suspenders and belt' approach: any two of the trio of the neck block extension, UTB, and A braces, could probably take most of the load. The UTB does help in keeping the end of the fingerbaord from dipping as the upper block rotates, but maybe it would not with the A braces there, and so on. It's a little extra work to put together, too, But you know, I do sleep o' nights, knowing that I've got a nice, solid structure up there, and several of my customers have commented on how stable the guitars are when they tour.

Well, I went way back in my photo archives (really only a few years) and found a pic of my take on Steve Klein's "flying brace". As you can see this does away with the traditional UTB and substitutes a "yoke", in this case made up of maple laminates and carbon fiber. It seems to eliminate neck block rotation, but the oldest one I've made is only about six years old (It's my everyday guitar and it gets abused pretty regularly) and it hasn't moved a bit. Check back with me in 20 years and I'll let you know how it's doing. As Al stated it's important that both ends of the yoke are firmly attached. These are attached to the neck block at one end and to the sides at the other end.

Just one more way of doing things. It works very well and produces a very nice sounding instrument. Great note separation and clarity and fun to play. Also fun to watch other luthiers reactions when they look inside the soundhole.

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Jimmy Caldwell
http://www.caldwellguitars.com

JJ,

Sorry - I've been away for a couple of days so am a little late with this - there's an interesting array of ideas and methods here in this thread already.

I've toyed with (and had a few discussions with Colin Symonds) about using his L-bracket neckblock with the fingerboard unglued and unbolted, but each time I shy away from the idea of having an area that the fingerboard is "pushing" down on attached to the top. This is the way I avoid any of the top fingerboard induced cracks. The neck shaft remains solid pretty much up to the beginning of the utb and is between 15-20mm thick. This is where I'm aming to get the best from neck playability, note clarity and energy transfer rather than gluing down on the top. With an adjustable neck joint system there are still issues (as have been discussed here before) of the neck shaft flexing and diving down a little into the top area but I have the germs of a few "cunning plans" about how to deal with this that may work out eventually.

So I'll illustrate what I do with pictures of the guitar I recently made for Sam Price. For my top bracing I have a soundhole patch flanked by two A-frame braces that are inlet into the neck block and straddled by the UTB:



The neckblock has a routed slot that the neckshaft supporting the fingerboard sits in:





And here's the rimset wth fb braces:



I do believe in the importance of the upper bout in sound production but these are subltleties - the sort that make the difference between a good chef and a great chef - BUT be aware you may not be a fan of this chef's particular signature dish! I believe you can get subtleties and complexities in the higher notes and harmonics from this area that gives me the sound that I am seeking.

Now, you'll note that my bracing in the upper bout is far from absent and minimalist. Well, I've said here many times before that when voicing a top, the brace that for me most makes the top come alive and responsive when glued on is the utb. Also I put a big side to side arch in the upper bout area. My utb is around 5-6mm wide, tapered and is probably around 10-12mm high in the centre but this varies with the instrument's size and design.

Hope this helps.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

I had Mike Doolin suggest putting the A type braces from the neck block back to the sides mirroring the buttresses as Todd Rose does and like Alan does. Although it was a suggestion as his guitars don't have a UTB because of the double cutaway design. I sent a PM to Rick Turner about this opening up the upper bout as he is working with it I believe. Sorry to say I recieved no responce and I didn't see the PM was ever out of the outbox so I deleted it. There is a past discussion here that Rick and Todd Rose discussed alot about this in a way where Rick uses carbon fiber in his center back brace and also in his linings. Might be worth doing a search to find that discussion. Nice to see the responces to this discussion since the only response I got to my discussion about opening up the top was to go and ask Rick Turner and Mike Doolin since I was using a Doolin adjustable neck joint and Rick was working around in this area of opening up the upper bout.

This is the discussion that has the info on the neck block and buttresses which I think relates to this discussion somewhat.
viewtopic.php?f=10102&t=14541&hilit=+Buttresses

Dave...Thanks so much for the details. It is encouraging to hear that you are squeezing more sound from the UB and that's what I am seeking. I'm making my first Dred which often lack the crystalline trebles that I so like in smaller guitars. My immediate thought was to open up the UB to help along in that regard. Your approach, while not possible on my in-process current build will definitely provide ideas for future designs. In the meantime, when I finish this guitar, I'll either have gotten closer to my goals or failed. In either case, I'll have something to build upon with the next Dred. Seems to be the way progress happens for me, at least.

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JJ
Napa, CA
http://www.DonohueGuitars.com