Official Luthiers Forum!

I am at the point where I have to install the center strips on the inside backs of the guitars I am building (classicals). Robbie's DVD doesn't make clear the dimensions or the grain direction (he assumes you are using a kit) of this although you can infer the dimensions from the photos and it does appear as thought the grain of the center strip runs PARALLEL to the back.

On the other hand, Cumpiano states that the center strip or Backing strip, as he calls it, should have the grain PERPENDICULAR to the grain of the back and this is the way that my personal guitar (GV Rubio) is made.

So, is the preferred method parallel or perpendicular? What are the advantages? I see a strength advantage going the perp route but what about the crossgrain glue joint?

Your help is greatly appreciated.

Steve Brown

Hi Steve

I have done mine both ways, but reached the conclusion that Cross Grained is stronger, and adds more stifness to the center seam

You got it right Steve, crossgrain is what you want.
Dimensions are not critical. John O. has a cool machine to do this, he took an electric plane, modified the base and made a moulding cutter out of the blade. Makes a beautiful arched strip from flat glued up pieces.

Some folks glue it on whole, and notch remove for braces. Others segment the material and install to a line or rule. Good luck, you had it already.

Perpendicular.

I think the idea is by having the grain perpendicular it will help resistance to the seam opening with the usual bumps, bangs and stresses a guitar usually encounters.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Hey Russell, sent you an email. bd

Wow!

Ask question, wait half an hour and you've got your answer! Thanks!

btw, I'm going to be doing the center srtip with crossgrain Spanish cedar. It smells so good.

Regards, Steve

Here is a simple little tool someone shared with me: A concave block with sandpaper glued in.

Perpendicular, I usually use a bit off the end of the back, if mahogany, or off the top if not. I don't think the wood type makes too much difference.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Perpendicular is the strongest.

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“If God dwells inside us like some people say, I sure hope He likes enchiladas, because that's what He's getting”
-jack handy

Perpendicular. I use the cutoff from the top, like Colin stated above.

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Dave Rector
Rector Guitars

Perpendicular here too. I use offcuts from tops, and I've now got a boatload of strips (enough for, oh, 15 guitars or so) in fine Italian spruce from a backer board I got with an old order from Rivolta; perfectly good wood, nice and stiff, 'cept for those two pesky giant knots running diagonally across the piece. Also have a baggie full of diamonds to reinforce the top center seam.

The "Perps" have it!

I knew I was dealing with a rascally bunch!

Actually, that name sounds more like a rock group!

Thanks, Steve

PS Dickey, I like the design. I think I'll make one.

Bob Gramman off the MIMF.

Another question on these, please. It seems I've seen them done in segments, divided by the braces, but also continuous with the braces notched to fit over top of the strip. Am I all wet? If not, what are the views of each method?

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DES - Shepherd, MI

They all work. It's simple, really. Strengthens the back join so it hopefully never splits. If we had an equivalent on the top, we'd have less top splits, I bet.

Even a few strategic diamonds would be great on some tops, especially larger guitars. But, honestly, I've never cleated a top.

I've only really seen them done interrupted; in theory I suppose there's a small stress riser at the intersection point, but it's not really in a direction cracks are likely to travel. And I cleat my tops, although I generally only remember once I've glued the top on already. Ahem.

I was asking because I like the idea of a continuous strip, but wondered if there was any worry of increasing the risk of the braces lifting in the center? Thanks for the input!

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DES - Shepherd, MI

The 'risk' I see in notching the braces over the centerstrip is the same risk that exists in butting up (but not inletting) side reinforcement strip into linings; a potential 'stress riser' parallel to the grain. As I see it, anwyay.