Reverse Kerfing

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Reverse Kerfing

Postby Andrew McSpadden » Mon Apr 23, 2018 3:35 pm

I am going back to reverse kerfing due to the side stiffening benefits but I was never happy with gluing it on. I don't like the faceted appearance in the inside and outside of curves and the occasional breakage.

Any tips people have on gluing these in would be helpful.

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Re: Reverse Kerfing

Postby Mike Conner » Mon Apr 23, 2018 6:25 pm

I lightly dampen the "web" with distilled water (to avoid any chance for discoloration) and that has greatly reduced the breakage. Warming it on the bending iron has helped also. //mike
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Re: Reverse Kerfing

Postby Barry Daniels » Mon Apr 23, 2018 8:58 pm

The faceted appearance is unavoidable. The thin web behind the kerf is the only place where it will bend. I suppose you could sand the face by hand or with a sanding drum to remove the facets, but that would just weaken the web, which is not advisable.
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Re: Reverse Kerfing

Postby Alan Carruth » Tue Apr 24, 2018 10:04 am

As Barry says, it's inevitable. I don't see how that's worse than the gaps in 'normal' kerfed liners. I suppose if you wanted it to really be smooth you could sand it and then glue on a veneer or cloth tape. That would make it even more rigid. Once you glue the top and back plates on the edge stiffness is the same for either sort of liners, as far as I can see. The added stiffness only counts before that. I do use continuous laminated liners in the upper arm of my harp guitars for strength. With kerfed liners or tentelones the load is all taken by the skins, where continuous liners can contribute strength and stiffness on their own, I think.
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Re: Reverse Kerfing

Postby Randolph Rhett » Wed Apr 25, 2018 8:15 pm

If you don’t want facets you need to use solid linings.
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Re: Reverse Kerfing

Postby Clay Schaeffer » Sat Apr 28, 2018 8:46 am

Another possibility is "semi solid linings". I have been making linings out of wacky wood (bending ply). It bends easily around the curves and to some degree in all directions - i.e. - it will follow the rise and fall of the sides. It adds a fair amount of stiffness to the sides. It is relatively cheap to make.
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Re: Reverse Kerfing

Postby Dave Meyrick » Mon May 07, 2018 3:51 pm

On another forum I saw that Roy Courtnall does kerfed linings in the usual way then glues a thin strip of timber on to the linings thus making a rather stiffer structure. It looks really neat and tidy.

It may also address the OP's concerns with the aesthetics of the faceted look of reversed kerfed linings.

My own concern is the quality of the glue joint of the kerfed linings with the sides around the very tight bends of the cutaway shapes that I like to build. I do reversed kerfed linings and they get very faceted round these curves, but more importantly it is really hard to ensure proper contact of the lining with the side round these tight curves when glueing.


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Re: Reverse Kerfing

Postby Bob Gramann » Mon May 07, 2018 5:33 pm

When I do reverse-kerfed lining around a tight bend, I often widen the kerf in that area so the lining can make the bend. I have never gotten too excited about the appearance of facets on the lining.
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Re: Reverse Kerfing

Postby Waddy Thomson » Tue May 08, 2018 2:21 pm

This may be laziness on my part, but I just love the A-4 Kerfing that Ryan sells. It's laser cut, bends in every direction and looks great. The only weakness I've found with it is that it is somewhat brittle, so has to be handled with some care. I do stiffen in the lower bout against the top with an outside/inside layer of something - usually Spanish Cedar - not because I feel it isn't stiff, but because I think an added bit of stiffness at the top join gives better projection.

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