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PostPosted: Fri Oct 02, 2009 9:49 pm 
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This is probably a dumb question but do you radius fan braces for a classical soundboard before gluing in a radius dish, or do you just radius the lower transverse brace and flex the fan braces to glue? And if you radius them, then do you cut them oversize, then radius and glue, and then carve down to size. I have cut all my braces to the size on the plans and then realized if I radius the fan braces they will get smaller towards the ends. Of course they will be scalloped anyway. How do most of you classical builders do this? Thanks, Wendy


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PostPosted: Fri Oct 02, 2009 10:19 pm 
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Just clamp your fan braces onto the sound board without radiusing them. You will achieve the dome by forcing the braces to the shape of the dome with the clamping pressure. The braces should be pretty close to size before clamping. I like to leave mine square and straight and do all the shaping post glue up.

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PostPosted: Fri Oct 02, 2009 11:23 pm 
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I was very skeptical about pressing straight fan braces into the curved soundboard, and expecting the dome to hold. I tried it out on a sample piece of wood, and, wouldn't you know it, it held perfectly!

I have recently taken to pre shaping them prior to gluing them in, at least the cross sectional shape. Some designs dictate gable shaped, some rounded over. I had often thought about doing this, then when I saw Luca Waldner doing it, I figured that I would be OK doing it too. (Luca did the restoration work on Torres' FE17). Leaving the fans square is easier to clamp, but its easy enough to think around that issue.

The harmonic bars are radiused or straight, depending upon your solara shaping. Their radius is shaped to match the solara prior to gluing in.

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PostPosted: Fri Oct 02, 2009 11:40 pm 
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I'm still in the process of building my first classical, so I'm no authority on the matter, however, this was a question that I came upon and answered myself, based on a simple test I did. I took a piece of scrap soundboard and cut it into two. To one piece, I glued an average sized classical fan brace directly, and to the other I glued a radius-sanded identical brace (from the same stick of wood). They were both glued up in the same radius dish and left overnight to set. As I suspected, the radius-sanded brace piece held its shape better upon release of the go bars. So my exerience was different from the other posters.

I radius-sanded all the braces in my first classical. YMMV.

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PostPosted: Sat Oct 03, 2009 3:45 am 
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The Spanish way is to press them in. I split my braces down to the last milimeter or so trying to ensure there is absolutely no runout in them. Radiusing their bottom introduces runout and I do not care for it considering the brace height on a Torres style instrument is extremely low.

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PostPosted: Sat Oct 03, 2009 4:34 am 
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Surely runout only matters if it's exposed to the air? That is, where the wood on one side of the runout can move independantly of the other. If a quartersawn brace with (very very) slight runout that is introduced by the radius sanding is glued solidly to the soundboard, it can't possilby split at those points, as there will be never be a differential force either side of the runout. Thus, runout only matters if it's on the top side of the brace. This applies equally to steel string guitars IMO.

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PostPosted: Sat Oct 03, 2009 6:10 am 
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I also press them in .
I use a go-bar deck of 30' radius.
They hold their shape perfectly .
I shape the #2 brace below the s.h. to 30' also and, the #1 brace is just about flat.


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PostPosted: Sat Oct 03, 2009 6:43 am 
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In a way I'm concerned about shock resistance. A thin brace with the fibers in the ideal alignment can be bent considerably more than one with runout. The runout piece will split sooner, with not much force needed, from my tests. The zero-runout brace has to be forced to the point of becoming rigid and only then it snaps with a loud "pop". Now, perhaps this is not of concern unless someone lands his butt on the bridge laughing6-hehe however guitars are occasionally subjected to all sort of trauma. Bridge taps required by some classical pieces, or flamenco golpes, might be included here too?

Also, extreme runout makes the wood a bit less stiff. The Torres type braces are just 3mm tall, and taper to nothing starting from behind the bridge, that means there is not much wood at all in an area prone to bulging. That's why I think it is wiser to choose the spruce carefully and eliminate as much runout as possible from near the glue line. I really feel it is structurally inferior.

Perhaps all this is just unimportant detail, but perhaps all the small detail added together makes for that better guitar.

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PostPosted: Sat Oct 03, 2009 11:36 am 
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Thanks for the replies. So Alexandru, are you saying that you think it is better to press them in without sanding them first to a radius because that introduces runout near the glue line? I am only referring to the fan braces here, and I am gluing in a 25' radius dish. I won't be shaping the braces until after they are glued, but I have cut them to the rectangular dimensions indicated on the Torres plan. I do plan on radiusing the lower transverse brace below the soundhole before I glue it. Speaking of shaping braces, I don't mean to change the subject, but the shape of Torres' fan braces is triangular down to the base of the brace, which is only 3mm high to begin with. Does anyone have any secrets as to the best way to do this shaping? Sorry for all the questions, but it has been 5 years since I last built a guitar and my brain and memory seem to have aged more like twice that. eek Thanks, Wendy


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PostPosted: Sat Oct 03, 2009 12:17 pm 
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Well, yes, because of the runout, and because everyone else presses them in, and it works without bothering with radiusing. Right before I glue them I run them on a bottom-up Jack plane and get a flat fresh shiny surface.

As for the shape, it depends on how dense is your brace stock, and how stiff/thick is your top. Torres' triangular braces might actually look more a house section, or gable end. I always thought it refers a perfect triangle but now I think you don't need to cut all the way down, but leave about 1mm of height, unless the spruce is exceptional. So the triangle is just 2mm tall, sitting on top of the 7x1 base. If you don't go all the way down you also avoid gouging the top with the chisel or miniplane you use to shape them.
Torres also made them half round and if you do the math you'll see this is a lot more meaty. Do this if you think your brace stock is light. Or if the top is not perfectly dead-on quarter. The trick is to try to compensate here and there for the wood-introduced-variety, if that makes sense :)

You must radius the bottom of the transverse bars to whatever dish/solera you use, indeed.

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PostPosted: Sat Oct 03, 2009 12:27 pm 
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As for shaping them, I like to use a freshly sharpened Japanese chisel Eat Drink . Make sure the bevel is nice and flat so you can use it upside down too. Recently I bought a flat bottom Herdim plane with a 9mm blade or so, it is pretty cool but I still like the chisel in most cases. I also paint some red pencil before I start, in order to keep the height intact.

Image

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PostPosted: Sat Oct 03, 2009 12:46 pm 
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From an amateur who had good success so far. I try to glue my braces to the top right away once I have made them and the bottoms are flat. I do not like to let mother nature play with them too long. I press them into the bowl in my solera using lead weights, and let them dry, and they hold the shape of the bowl. Quite fun!

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PostPosted: Sat Oct 03, 2009 1:02 pm 
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That is great advice on the shaping of the braces. I would have shaped them with a chisel but, since I thought the triangle should go all the way to the bottom, I was afraid of gouging the top. I am building 2, one top seems very stiff and the other not. I will vary the shape of the braces accordingly. Thank you Alexandru. I will also press the fan braces in, rather than sanding a radius on them first. I'm anxious to get going on the bracing, but I want to bend the sides first, and then hold the sides in a mold. That way, if something goes wrong with the bending, I'm not stuck with a braced top sitting around while I figure out where to get new sides. I am just waiting for the arrival of the heating blanket I ordered from John Hall. Thanks all, Wendy


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PostPosted: Sat Oct 03, 2009 5:48 pm 
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That the sprung in place fan braces do not retain the dome "perfectly" is inconsequential as all of them will be equally imperfect.

The degree of doming is not a critical design feature unless it changes dramatically from the specs. Ie. if the dome is supposed to be 3mm and it comes out as 2mm, that is insignificant. If it was supposed to be 5mm and it comes out as 2mm, that IS significant.

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PostPosted: Mon Oct 05, 2009 11:17 am 
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I get, almost, no spring back from my braces in a 25' radius. Actually, it ends up being closer to 15 by the time the lowering of the wings is done. However, I spring the flat braces in, and do all the carving after, but leave the holding caul in place until the bridge is glued on. This maintains the top radius throughout the build. When the bridge is attached, it maintains the dome from the outside. However, I still don't see spring back, even if I take it out of the solera. Here are some pictures of my second guitar top when taken out of the solera. This was for a discussion of top geometry on another forum.

In the Solera.
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P1010559 (Large).JPG


Raised lower bout.
Attachment:
P1010560 (Large).JPG


Out of the solera.
Attachment:
P1010562 (Large).JPG
Attachment:
P1010563 (Large).JPG
Attachment:
P1010566 (Large).JPG


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PostPosted: Tue Oct 06, 2009 10:58 am 
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I'm not sure I could get a vacuum lid in place without moving 7 fans that are 3mm wide by f - 7 mm tall. Using a go bar seems the easiest way to do it, to me.

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PostPosted: Tue Oct 06, 2009 12:00 pm 
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Dave,

See pp. 113-114 of the Romanillos book on Torres, where
this issue is discussed directly.

Benefits claimed for not radiusing the fan braces, or "struts"
as he calls them, are speed of construction and increased
structural strength (due to the intact "longitudinal fibers").

Cheers,

Eric


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