Q on bracing the back

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Greg Carter
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Q on bracing the back

Post by Greg Carter »

This is my first acoustic build. It is my understanding we glue the back seam reinforcement first, before the back lateral braces. We mark where the laterals will go, and chisel out the seam brace at the intersection. It is not notched, but chiseled away (down to the bare back wood).

Why? Why not glue the laterals in first, then snug-fit the seam brace between each one? Or, why not cut a very tiny dado in the seam brace and notch the lateral brace?

Is this just tradition (cue music from Fiddler on the Roof), or is there a substantive integrity issue here?

Disclaimer: I have received most of my education on this matter by watching Youtube videos, reading the Kinkade book, and listening to those voices we hear as we drift off to sleep (you get them too, right?).

Thanks.

Greg

Chuck Tweedy
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Re: Q on bracing the back

Post by Chuck Tweedy »

It is actually very easy to get a real snug, clean looking fit do it the traditional way.

Pasting in sections of marriage strip has 2 difficulties: getting a snug fit against the brace, and keeping the strips in alignment with the those on either side of the braces.

It's not a super critical part of the whole package, so do it the way you want to.
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Charlie Schultz
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Re: Q on bracing the back

Post by Charlie Schultz »

It is my understanding we glue the back seam reinforcement first, before the back lateral braces. We mark where the laterals will go, and chisel out the seam brace at the intersection. It is not notched, but chiseled away (down to the bare back wood).
That's the way I do it for classicals. You could argue that the center seam should be glued first, since the seam is the weak joint and you'll be stressing it (slightly) when the back is arched when adding the lateral braces. I think it is easier to clamp that way too, but like Chuck said, you can do it either way that works for you.

Rodger Knox
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Re: Q on bracing the back

Post by Rodger Knox »

As Chuck said, do it the way that makes sense to you. As with many of the building operations, the "traditional" method was the quickest and easiest way with the skills and tooling of 100 years ago. Some may still be quickest and easiest, others may not. In any case, the "traditional" methods are not necessarily superior structurally or acousticly, but they_MAY_be. :lol:
A man hears what he wants to hear, and disreguards the rest. Paul Simon

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Waddy Thomson
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Re: Q on bracing the back

Post by Waddy Thomson »

I do it the backwards way. I even fit the braces into the body, put double stick tape on them, set the back to the braces, align, press down and lift the braces out of the body. I clamp the brace ends in place, put tape dams on the ends and both edges, and glue them to the back. Then I fit the back strip pieces, and use a caul with cut-outs for the brace locations to align the pieces. Seems convoluted, but it works for me because my brace ends are at full height at the ends, and scooped in the center, and they sit on brace blocks glued to the sides. I also install my back lining with the braces sitting on the blocks. Easier to fit.

This picture is just before putting the tape and fitting the back to the braces. Everything has been sanded to the radius.
P1060151 (Large).JPG
Tape dams in place to glue braces down.
P1060157 (Large).JPG
Glued and ready to fit back into the box.
P1060163 (Large).JPG
I have tried it the other way, and every time I did, something went wrong. I've done the last 9 this way without a hitch, so far. The back braces are loose fit, and not glued to the sides, except for the block, to allow for expansion.

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Peter Wilcox
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Re: Q on bracing the back

Post by Peter Wilcox »

I've only made two backs - one each way. It was definitely faster and cleaner to glue and clamp, then shape, the seam reinforcement as a single unit, and then cut slots for the lateral braces and glue them in.
Maybe I can't fix it, but I can fix it so no one can fix it

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Mark Swanson
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Re: Q on bracing the back

Post by Mark Swanson »

I do it as Peter says...I glue the strip on first, and then just chisel out the gaps for the braces. It's easy and fast, use a sharp chisel and fear not.
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Layne Campbell
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Re: Q on bracing the back

Post by Layne Campbell »

ha Waddy,

Why does your purfling that is holding the soundboard to the sides look different from mine? did you use a bunch of individual pieces?

-Layne

Dennis Duross
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Re: Q on bracing the back

Post by Dennis Duross »

I suppose there's another way, which would be to alternate gluing in seam strips and braces. Start with the short seam piece nearest the tailblock. Then glue the lower bout lateral brace, then the next section of seam, etc. No chiselling required (as is necessary if you lay in a full length of seam first), and no issues with getting snug fits (as is the case if you lay in the braces first).

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Waddy Thomson
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Re: Q on bracing the back

Post by Waddy Thomson »

Layne Campbell wrote:ha Waddy,

Why does your purfling that is holding the soundboard to the sides look different from mine? did you use a bunch of individual pieces?

-Layne
If you are talking about the linings, in classical guitar construction, they are usually referred to as tentellones. Romanillos said that was a published error and they should be called dentallones(as in dental molding). Anyway, they are individual little triangular pieces glued to the sides and top with hot hide glue or fish glue. Each is held in place until they tack well, then the next is placed and held. The alternating sizes is a way not to have to worry too much if they aren't all exactly the same size.

Mario Proulx
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Re: Q on bracing the back

Post by Mario Proulx »

I have yet another way..

I make my center reinforcement strips in short sections(all from matching stock) that relate to the distance between the back braces(and blocks). I make these in batches, then set them aside, in order. One end of the strip is cut perfectly square. In use, I first mark the brace location on the back, then clamp a straight edge exactly 3/8" off the centerline(the strips are 3/4"). I glue the strips with the square end right against the lines, which will be the front edge of the brace.

Once dry, I can shape the strip(I like to see a nice radius on it), then I take each brace, hold it against the squared end of the strip, and with single-edge razor blade held tight to the brace, "chop" through the centerstrip. A 1/4" chisel them lifts-off the waste piece, a slight clean up is done, and onto the next one.

This gives me a very tight fit between the strip and braces, and also holds the braces in place while gluing!

It's only slight different from the method of gluing down a full length strip, but it has some advantages, is simpler, and I can use shorter lengths of spruce. I found a 2x10 some years ago that had about a 6 or 7 inch wide strip of vertical grain, and very few knots; I ripped it full length at the 6 or 7 inch mark, and cut it into 2 foot lengths. When I need to make some new center reinforcements, I take one of the 2' lengths, cut it carefully into 3/4" lengths, and then slice these to about .100" thickness, and set them aside, in order. After an hour or so, I'll have hundreds of strips! I then take a simple marking gauge, mark and cut each set to length, then they go into a small parts storage cabinet. A couple hours' work every few years....

Tyko Runesson
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Re: Q on bracing the back

Post by Tyko Runesson »

There is different ways of doing nearly everything. The way to nothch the braces so that they fit snugly over the centerstrip is used on Takamine guitars for example.
I prefer to glue the centerstrip in one peace. If I like to use some shorter strips I can easily join them unvisible when I glue them down. After gluing down the centerstrip it is easy to shape it as I like it and that is one of the good thing with this way I think.

Hugh Anderson
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Re: Q on bracing the back

Post by Hugh Anderson »

I glue in the center strip first, that's the only way I can get it straight.

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Charlie Schultz
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Re: Q on bracing the back

Post by Charlie Schultz »

Hi Hugh and welcome to the forum!

Ron Belanger
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Re: Q on bracing the back

Post by Ron Belanger »

I like Mario's method, I do something close, but cut on both sides of the brace. Not simple enough.

Steven Odut
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Re: Q on bracing the back

Post by Steven Odut »

My guess is that if you glue the centre strip down first, then you can easily shape and sand the strip while it is in place.

If you glue the braces in first and fit the centre strip pieces between the braces, then sanding the strip in place is more difficult and you have to do your shaping before gluing the strip in place.

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Waddy Thomson
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Re: Q on bracing the back

Post by Waddy Thomson »

Yep - double stick tape and the edge of a 3/4" board. Roughing with a plane then finishing with a rounded out sanding block with the correct radius.

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