Why is lining kerfed instead of heated and bent?

[StevenS]

Seems like a smooth lining would be better in the sound chamber.

What are the benefits (beyond ease of bending) for kerfing the lining strips?

Thanks,
Steve

[Stephanie Reiser]

It's a good question, and I don't really have a good answer.
Violins and classical guitars don't use kerfing, instead having "lining", albiet a narrow one.
Whatever the case, it is to provide for thickening the side for a better gluing surface. But bending unkerfed lining for mandolin or guitar would be hard, as it tends to be rather thick. Hence the sawing of kerfs. Kindof like kerfing the bottom rise of a staircase that wraps around a newel post. Needs to be kerfed for bending. Kerfing is both a verb and a noun in this sense.

[Dfyngravity]

Being that it is not solid would seem to be good in my view since it reduces the overall weight of the mandolin.

[Bruce Evans]

Originally Posted by StevenS

Seems like a smooth lining would be better in the sound chamber.

Huh? What is your reasoning for that?

What are the benefits (beyond ease of bending) for kerfing the lining strips?

Kerfing simply gives more gluing surface than a lining. The thickness of the backing strip of the kerfing is about the same as the thickness of a lining.

[Dave Cohen]

(a) You can use solid linings if you want. I have done some experimental ribsets that way.

(b) Solid linings are a bit more work. For each lining, I thicknessed three layers, then bent them individually, then glued them into the ribset as a sandwich.

(c) There are advantages and disadvantages. If you are looking for rigidity in your ribset, the soild linings can give you that. I haven't decided whether or not greater rigidity of the ribset is an advantage. It should be according to Bernard Richardson's models, but maybe not so important in the conventional two-oscillator and three-oscillator models. On the other hand, solid linings do add mass, and they are a bit more work. To get the mass down, you would have to shape your solid linings creatively. ...Which is another point in itself; you will have to do some shaping after you glue your solid linings into the ribset. Users of kerfed linings usually preshape their linings prior to gluing them in.

(d) Another alternative is "reverse kerfed" linings...kinda part way between traditional kerfed linings and solid linings. More rigidity that traditional kerfing, similar mass. Otoh, some shaping required after gluing in.

(e) If you are worried about the kerf cuts being little "holes" inside the soundbox, you can stop worrying about that. The dimensions of the "holes" are very small compared to even the shorter wavelengths of either cavity air motion or motion of the mandolin body. Essentially, the air resonances up to the third one (ca 1.1 kHz) don't even "see" features the size of kerf cuts. Same deal for the important body modes. To the important motions of mandolin bodies, the kerf cuts wouldn't become noticeable features until frequencies in the hundreds of kHz. For reference, the hearing of a young adult human poops out around 20 kHz.

http://www.Cohenmando.com

[Big Joe]

While bending can be a way to do the kerfing, it can add some tension to the rim that is not needed and could be problematic as time goes by. Should the rim/top become seperated the tension on the bent kerfing could force the rim out of shape so it would be a bit harder to get the rim/top back together again. By butting the curfing and bending it you remove the tension in the wood kerfing and eliminates that extra force where it is not desired.

[sunburst]

I used "standard" kerfing, tried " reverse kerfing" for a while, went to solid bent linings and that's what I'm using now. It all works fine. The only differences I see are in how easy or difficult they are to work with in the various stages from making them to installing and finishing them.

[Lefty Luthier]

I have tried kerfing in both directions and solid laminations and found no difference in performance. The solid laminations take a bit longer to make but otherwise seem to work just fine. Generally, I use reverse kerfed more out of habit than any technical reason, it does seem a bit easier to clamp.

[swampy]

It would seem to me that a solid lining would be fine for a violin due to the fact that the top overhangs. On a mandolin, the top would be cut back leaving only a small surface area actually glued to the solid lining. The rim itself would only support the binding? Right? Wrong?

[Frank Ford]

Linings are kerfed, I think, for only one reason - to save time and money.

Some elegant vintage guitars had solid back linings and either those little triangular lining pieces or kerfed top linings where they would not be visible through the soundhole.

Kerfed linings would be pretty small inside a violin, and would crumble like crazy during top and back removal - part of many common repairs.

And, no, I don't think kerfed linings could possibly have an effect on tone, except for 1/16 notes - their pointy tails might get caught in the cracks. . . (Nuyck, nyuck - I'm too old to use smilies.)

[sunburst]

Originally Posted by Frank Ford

And, no, I don't think kerfed linings could possibly have an effect on tone, except for 1/16 notes - their pointy tails might get caught in the cracks. . . (Nuyck, nyuck - I'm too old to use smilies.)

(I just did that mostly to show how much younger I am than Frank...)

[Dave Cohen]

Violin linings are ca 2 mm wide, giving about 3.5 mm total gluing surface width for the plate-ribs joint. As I mentioned above, and also as John apparently does it, the total width of laminated solid linings in mandolins and guitars are wider, typically the conventional width of kerfed mandolin linings.

'Tension' refers to externally applied forces at opposite ends of an object. Strictly speaking, what Joe is referring to is an internal 'stress'. Over long times (ca months to about a year), stresses in wood tend to go away. Unless, that is, the wood object is subjected to external stresses during its lifetime. An example of that is the common problem of the seam between the back plate and the ribs coming apart at the tailblock. The forces from string tension tend to deform the ribs in that area once the glue seam has broken. The deformation itself is referred to as 'strain'. Strain can be reversed. Frank Ford has a nice example on his Frets.com website of how he deals with the above mentioned strain from the backplate/ribs separation at the tailblock.

http://www.Cohenmando.com

[sunburst]

I neglected to mention that my solid linings are not laminated, but instead are strips of wood about 3/16" thick or a little less, heat bent to fit. After they are installed I carve them to a triangular profile with a convex sole finger plane, forming what I see as a graceful contour. Too bad nobody sees them!

Those little sixteenth notes can't find a place to hang their pointy little tails so they burst forth through the f holes!! Well, so much for my snake oil selling talents...

[nkforster]

I'm with Frank on this one. Kerfed linings can be made up in large quantites and with little skill - ideal for production. Another advantage is a kerfed lining will conform to the ribs where there can be a tendancy for ribs and linings to fight one another if the latter have not been bent to meet the sides exactly. I've seen pictures of folk using heavy spring clamps to glue solid linings, but there should be no need for this much pressure, clothes pegs should be enough. If they are not, you need to fit the linings better.

I've used both kerfed and solid linings in my instruments, and I doubt if they make much difference to how the instruments sounds. There are many factors which are more relevant to tone production and projection.

When you consider the depth of your binding need not be deeper than the thickness of the top or back, and the purfling less so, there is no need for large linings in a Mandolin unless you have convinced yourself they make a difference.

These days I use offcuts from scrap guitar soundboards for my linings, which are thin, light and bend quickly without problems. If I want rigidity at all from my linings it is to add stiffness from tail to neck and small solid linings perform this task better than large kerfed ones. They look nice too.

http://www.nkforsterguitars.com

[Rick Turner]

On guitars I now laminate a strip of CF that's .021" thick by .250" wide on top of reverse kerfing. On the last one I built, I then bound the top with three layers of the CF. If you want a nice stiff rim for the top, that's one way to do it...

[nkforster]

That's a great idea Rick, what is it like scraping that stuff down though? What about the dust getting into the Spruce. Mmmm got me thinking that has...

http://www.nkforsterguitars.com

[sunburst]

Rick, you might not even need cases for those guitars!

[Lefty Luthier]

Originally Posted by Rick Turner

On guitars I now laminate a strip of CF that's .021" thick by .250" wide on top of reverse kerfing. On the last one I built, I then bound the top with three layers of the CF. If you want a nice stiff rim for the top, that's one way to do it...

That sounds like a great way to go. Think I will try that on my next instrument.

[Richard Sanabia]

Wow, my sixteenth notes MUST be getting caught in the kerfing because my smarty pants fiddle playing wife will occasionally holler at me that the notes I am playing aren't sixteenth notes, but something else, and I need to get the metronome and practice AGAIN! yada..yada...yada...

[grandcanyonminstrel]

I use a solid, unkerfed linings for all of my instruments- from the mandolin up to the double bass. It is usually made from one of the aromatic cedars. I already have a nice heat blanket bending sytem for bending the sides and wooden binding. It only takes a few minutes more to bend my linings in the same machine. For more complex bend- like the inside curves on a hollow scroll (no F5 style giant block), I bend solid linings and then micro-kerf them with .015" razor saw to get the fit even more snug.

The best I've been able to bend a softwood is just a hair under 1/4" thick; at that range, you get a few compression bends if the radius is too sharp. You've got endless options for laminating them. Structurally, a solid lining is very rigid compared to a kerfed one. I've also seen a lot of classical guitars built with an adaptation of Richard Scneider's Kasha system guitars where the back plates are glued directly to the ribs and then an epoxy ramped dam is spread at the 90 junction, similar to caulking a window or bathtub with silicon.

Kerfed linings are pretty easy to make in large numbers in a production setting and they go on so fast that they made up one of the many things that allowed me to build two mandolins every day, before lunch, when I worked at "the mandolin factory"...

j.
www.condino.com

[StevenS]

Thank you for the detailed responses. My 16th notes are so slow-moving about half of them seem to get stuck somewhere before they get out of the f-holes. Now I can blame the Kerfs. . .

Makes me want to try solid linings.

Steve

[fishtownmike]

I see one advantage of kerfing is that the glue will grip into the kerf cut for better adhesion then a solid lining. Now this is just my thoughts as i never did a experiment to prove this.

[Hans]

I use kerfed linings for two reasons. One, after bending a set of ribs and gluing them up to the blocks on the mould, I'm sick of bending, and two, it doesn't make a dang bit of difference once you glue on the top and remove the assembly from the mould.

[Dave Cohen]

"...the glue will grip into the kerf cut for better adhesion than a solid lining."

I don't think that blobs of glue which are not between two surfaces will have much, if anything, to do with either the shear or tensile strength of a bond between the two surfaces. The only exception to that is the gluing of Nomex to wood surfaces. Because of the very small surface area of the Nomex honeycombs on end, the glue has to climb up into the honeycomb cavities by capillary action in order to increase the surface area being glued. Not a good analogy to reverse kerfed lining being glued to a rib surface. That, and the blobs of glue add unecessary mass.

"....and two, it doesn't make a dang bit of difference once you glue on the top and remove the assembly from the mould."

Not quite true. A stiffer lining/rib assembly will be stiffer with respect to the whole-body barlike bending motions, or "corpus modes", and consequently those corpus mode frequencies will be higher. Now, "how much higher?", and "how much difference does it make to things like sound radiation?" -- I don't know. But I am getting ready to do some experiments to attempt to find out.

http://www.Cohenmando.com

[Mario Proulx]

I use solid linings; for no other reason than I'm too cheap to buy pre-made kerfed linings, and too lazy to kerf my own

Actually, I like the look, and I enjoy bending wood. No more, no less. In the end, it does cost me less(I just use the off cuts from the ribs or small pieces leftover from some other job, as linings) and indeed takes less time. And like John, I go back over them with my smallest finger plane and round them over some. If there's an structural advantage or not, I won't even guess.