Official Luthiers Forum!

I came up with this idea after seeing photos of Gary Southwell"s "A Series" guitars in the winter 2009 issue of American Lutherie.

The braces are laminated with hot hide glue, and are a sandwich of spruce and mahogany. I don't have any real compelling reasons for this scheme other than having a brace connect the neck/head block to the tail block might help prevent some deformation in front of the bridge. I'll be using a Doolin style pin-less bridge.

I'm wondering if there will be enough lateral strength to this design.

I assume this is not glued, but that everything is simply sitting in place to show the concept for feedback? If it is glued, what is the purpose for everything being so off center?

_________________
Bill Hodge


One does not simply, own enough guitars!

By first glance, it looks way to stiff to be able to move the top up and down. is there a reason behind the braces are not laying centered ? (neckblock ) . Looks cool though !
How does she sound when tapping ?

Lars

Seems over braced to me Cool looking tho Clinton

Am I right in saying that the curves of the braces add a lot more stiffness to the top? If I'm correct, I'd think that this particular top would be way over braced. However, it would be interesting to see this concept evolve.

The braces slid off center during glue up, and I haven't gotten around to re-gluing them. The top and braces were glued up in a 15" radius dish. The 3 central braces are 1/2" by 1/2" and are scalloped and tapered. The 2 outer braces are 14" wide, and 1/2" high and are also scalloped and tapered.

The top taps fairly well, although I think the braces could be shaved a bit more. As press on the top and compare it to my other guitars, (a J-200 and an Alverez /Yari dreadnaught) the amount of deflection seems similar. (not a very exact method I know, but it's what I've got.)

Thanks for your input - I'll post more as the project moves along.

Jim

Looks like a lot of cross dipole movement and not so much long dipole. Wonder how it would sound?

Chuck

_________________
_________________

Chuck, could you expand on cross dipole movement vs. long dipole movement for a non engineer type?

Jim

That particular layout would probably have high longitudinal stiffness and relatively low lateral stiffness. The long-dipole freq would probably be high, and the cross-dipole freq, low. I would omit the large bar along the centerline.

I don't think the braces need to go directly to the headblock--any connection near there will be stiff enough to resist top depression, as the siding makes a ~rigid wall lateral to the headblock (also the offcenter sound holes makes it even stiffer there).

The dual soundholes throw another variable into the mix, unless you normally build that way. If not, I'd suggest building another with a standard soundhole, so you have a better idea of 'what caused what'.

Here is another take on this approach:
http://www.goreguitars.com.au/main/page ... acing.html

_________________
David Malicky

Interesting. You could easily get away without that massive center bar and still have a strong and stable top from what the picture looks like. I think you will lose alot of the top's vibration ability and choke it to death by having that big one in there. I do like the notion of vibrations being able to travel farther and be directed around from the bridge area through the swooping braces. I myself envisioned something similar where the bridge plate almost has spider like legs that creep in all directions from center and reach varrying thicknesses as they make it towards the rim. My thoughts were that they would help amplify the vibrations of the bridge, and since there would be more of them than on a normal X-bracing that I could make them much smaller so they would perhaps act like finger braces and not have to support as much of a load an an X brace would. Interesting design though, make sure you let us all know how it sounds.

_________________
http://www.sixgunguitars.com

I do like the concept. I agree with those who recommended losing the center brace. That will choke vibration across some of the most important areas of the top.
It would also be good to see something that would help limit the rotational forces and stresses that are going to be held up by the neck block. An upper transverse brace would be good, or maybe CF rods anchored between the two blocks or something like that. You just need something to counter all the tension the strings will put on the neck end of the guitar.

Food for thought.

It would also be intersting to run an FFT scan and find out how the top vibrates.


Good luck.

Dave

I also agree with losing the middle brace. I built two small steel strings last year that had bent laminated bracing and found that the bent laminations add an insane amount of stiffness to the top. I built an access panel into the back so that I'd be able to experiment with them and I shaved off a ton material to get it to a point where it could actually move freely. They both had a ton of sustain, but really lacked in the bass end. Good luck with it and let us know how it turns out.

Do you think there's a risk that it will split down the center seam with any humidity swings? Without a lateral support (either x brace or "cross bar" on a ladder brace) looks like there might be some stress on that long center seam.

Just wondering how you plan on accessing the interior for repairs or even to bolt the neck in place (since I see a mortise, I assume you're bolting the neck on). The soundholes appear too small for my hands, at least.

With an experimental design, access is pretty important. There are no finger braces to support the outer edges so there may -- may -- be a tendency for the soundboard to crack in those areas. There's minimal support for the fingerboard extension and, even with the offset soundholes, the top may tend to deform there. If you could get inside easily, you'd have the option of adding a transverse brace at a later date without pulling the back.

Whatever, good luck. I'd love to hear it when it's done.

My thought is, "How about you explain your thinking?"

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Except for the additional main center brace, it looks like a X-brace pattern.

_________________
https://www.facebook.com/profile.php?id=100008907949110

One other thought, be careful routing the back binding with the open mortise.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

My first thought in looking at it is that it's way over done. The stiffness longitudinally is going to be off the charts as laminated curved braces are incredibly stiff. I tried using a hybrid X with some laminated curved braces (only spruce lams) and it was vastly too stiff and the guitar had no bass response hardly at all. I think you might have got caught up in the "cool idea" route, which does not always translate (usually does not) to a good practical design. I've done that too many times, but we live and we learn.

I could very well be dead wrong (as my wife reminds me daily) but I doubt this scheme, as it is presented, is going to make for a stellar sound.

_________________
John Mayes
http://www.mayesluthier.com

Curves add stiffness in line to the curve. So if you build an arch you get extra stiffness to resist the effect of gravity. You don't get extra stiffness relative to a wind load parallel to the ground. I don't think these curves will add stiffness that will affect top mobility, they do add weight though. For a steel string you have a chance, depending on a lot of things I can't see like top thickness.

http://www.crane.gr.jp/more/2008Concept6/

If I was going to be experimental with that design,
I would just use the outer braces,
and use a bunch of finger braces to hold the shape of the top.

One of my touchstones for steel strings was the Tacoma guitar. I think they have taken down their bracing outlines. All the bracing was the same and something like maybe 5x15 mm. They used only two braces to make an SS top, with offset soundhole, and no waist bar. The plates are @ 3mm thick. I call it a touchstone, but in the structural sense. So in your case you have a similar full face board, and what looks like a lot of braces.

http://liutaiomottola.com/

This site contains some guitars also inspired by the simple Tacoma style, you might get some numbers there to compare.

Anyway, don't expect too much from others. Make what you want. Many people won't go off the straight and narrow, and they certainly won't endorse the specific excursions of others.

Thanks for all the feed back so far.

My original thinking on this came from a video on Fine Woodworking's web site, where a guy was band sawing a board towards the centre lengthwise from from opposite ends, with the cuts being offset from one another, to allow him to pull them apart horizontally and form some interesting shapes for bases for tables or cabinets. My idea from this was to make a one piece brace, somewhat like spokes on a wheel. I was unable to make that idea work, and this was the result of my continued thoughts.


My thinking with the centre brace was to continue getting neck vibration into the top. (although I wonder if this might contribute to wolf notes). I was thinking this bracing might form a top more resistant to deforming near the bridge.

The neck will bolt on to a T nut mounted on the inside of the head block, with the Allen head bolt accessed from the heel of the neck. (Mike Doolin style)

If I feel this design merits continued experimentation, I'll change the two sound holes to crescent or modified F holes nearer the waist since I think that aesthetically this is starting to look ike a hoot owl or some goofy face.

So - thanks for the feedback. I think I'll keep the center brace, but shave it down quite a bit and perhaps thin the other braces a bit too, as the top does seem pretty stiff.

I'll post more as progress happens.

Jim