"Squiggle Wood" Coved Kerfing

Aloha,
Just thought I'd share the latest shop creation. The cove, in my eye, adds a bit of elegance to the kerfing.

That looks very nice Don. Good for some applications. Personally for me though I make my kerfings with a reverse cove (I don't know what that shape is called, it convex instead of concave.) All of my ukes are bound and all have some kind of purling on them, some, in the case of shell, are pretty wide. As I'm cutting those channels in I want to make sure I have enough kerfing for support. In the case of rope purling I'm cutting deep enough to expose the notches so I've got to be careful. Just one more thing to think about when designing these things. For simpler ukes though it is quite attractive.

Moore Bettah Ukuleles said:

. Personally for me though I make my kerfings with a reverse cove (I don't know what that shape is called, it convex instead of concave.)

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"quarter round"

Stagehand said:

"quarter round"

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Doh! Thank you.

Moore Bettah Ukuleles said:

That looks very nice Don. Good for some applications. Personally for me though I make my kerfings with a reverse cove (I don't know what that shape is called, it convex instead of concave.) All of my ukes are bound and all have some kind of purling on them, some, in the case of shell, are pretty wide. As I'm cutting those channels in I want to make sure I have enough kerfing for support. In the case of rope purling I'm cutting deep enough to expose the notches so I've got to be careful. Just one more thing to think about when designing these things. For simpler ukes though it is quite attractive.

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Thanks Chuck,
This is version 1.0 and will be improved upon. If kept "rectangular" there is more than enough meat on them to support the application you are talking about. Don't know if you can see the kerfs in the pictures, but the cuts are essentially the A4 kerfing except with a cove instead of a chamfer. I am playing with varying the width which would create more meat for binding/purfling applications.

Critical feedback is appreciated. I'm looking to improve on the design.

donovan

I like it! Both concave and convex could have their advantages depending on the build your doing.

And the advantages of he concave style would be.....?

Coving type linings do look quite nice.....But are they as strong as convex ones or standard triangle ?..answer No!:rulez: concave is more prone to splitting...
I went thro' all this stuff yonks ago when I was involved in construction and welding...I can remember a whole section of an oil rig platform being re-welded due to reject concave fillet welds...But that was Steel not wood ...But the same physics apply... they do look nicer tho'

Moore Bettah Ukuleles said:

And the advantages of he concave style would be.....?

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Background into the design philosophy (from my end). First off, I can never tell the difference between concave and convex so I will use my language of cove vs. quarter round. Not suggesting that one is better but instead that each has its particular application. I designed the cove to 1) maintain surface area for gluing surfaces 2) minimize weight 3) improve (in my eyes) aesthetic appeal. The soundboard face glueing surface is maximized. The side face glueing surface is maximized. Weight is reduced by removing material from the areas which are not attached to or used as glueing surfaces. The disadvatage/expense of the weight removal by using the cove, as opposed to the quarter round, has already been addressed in your previous post. So both the cove and quarter round are successful in 1) Maintaining surface area. 2) The cove has an advantage over quarter round in weight as it weighs less (assuming the design philosophy that lighter is better. 3) What looks better is subjective. I personally like smooth curves more than straight lines (triangle kerfing) and in my eyes the quarter round goes the "wrong way" with the natural shape of the instrument so I feel the cove is more aesthetically pleasing. Other's may disagree on this and that is okay. Also for those who believe that round surfaces help the sound more than straight/square surfaces both the cove and quarter round are successful in accomplishing that.

I see the cove design's biggest advantage if being used on an instrument back that has no purfling (binding okay with some minimal modifications to the thickness of the coved kerfing) because it is visible through the soundhole and no concerns about purfling in that scenario. If the cove design is used on an instrument back, it maximizes all of the advantages and none of the drawbacks (assuming no purfling is being installed on the back).

The picture I included in the original thread, looking through the soundhole, was strategically chosen because I felt that it showed the coved kerf design in it's optimal location, optimizing strengths and limiting weaknesses. With that said I'd use something besides the cove on the soundboard because it's less visible and no one will see it so the only advantage of the cove design in that scenario would be the weight savings but at the expense of function for binding/purfling install which for that tradeoff is not worth it.

All of these comments are based on me spending the last 5 hours in the shop working on different designs and trying to improve on the design based on Chuck's and other's comments and my own thinking by experimenting with kerf heights, widths, etc. No pictures yet, but lots of sawdust and kerfing on the table.

Open to further critique and constructive criticism Thanks for asking Chuck. This helped to make things in the design explicit. As I was writing I realized some of those things might not be obvious. I sometime forget that other people can't see inside my brain

We have not discussed the issue of lining/kerfing stiffness but that conversation has a lot of assumptions that would need to be laid out first.

donovan

Timbuck said:

Coving type linings do look quite nice.....But are they as strong as convex ones or standard triangle ?..answer No!:rulez: concave is more prone to splitting...
I went thro' all this stuff yonks ago when I was involved in construction and welding...I can remember a whole section of an oil rig platform being re-welded due to reject concave fillet welds...But that was Steel not wood ...And the same physics apply...But! they do look nicer.

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Thanks Timbuck for adding to the conversation. Would you say that the analysis/physics of an oil rig platform, which has a structural function (it supports the weight of the entire rig), holds in the context of the function of lining/kerfing on an instrument? Sincere question. In my current thinking, it seems that the analogy is different. Not doubting the physics on the oil rig but instead wondering if the analogy is applicable to a musical instrument. Oil rig platforms don't have kerfs? Would the kerfs help to reduce the surface tension described in your diagram? Also this particular design is kerfed on opposite faces. Would such a design not further relieve the surface tension? In my mind, linings/kerfings are more of a glueing surface rather than a structural support for the top. If they were primarily structural support I would think we would all be using thick and solid laminated linings? But I do agree that they look nicer.

Draw a straight line connecting the two ends of the concave weld and we get "triangular" shaped kerfing. I wonder if those hundredths of an inch material difference between cove and triangular kerfing make that much of a difference in structural terms? Not denying the theoretical difference on paper but in an actual instrument is a top going to fail and implode because of a cove kerf vs. a triangle kerf. I realize the quarter round shape is stronger than both because it has more mass at the (expense of weight). We shave our braces/tone bars to "optimize" strength/weight ratios.
***Added
Timbuck I was writing response #9 to Chuck's question and then saw and read your reply. We must have been typing at the same time.

Moore Bettah Ukuleles said:

And the advantages of he concave style would be.....?

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Howzit Chuck,

Decreased mass in the center of the kerf but with same gluing area (as convex) for top and back support when clamped up. I believe the one I made at Don's shop was an asymmetric concave with a taper blending into the side.

Mahalo,
Kālewa

Kōāpa‘a;1475038 said:

Thanks Timbuck for adding to the conversation. Would you say that the analysis/physics of an oil rig platform, which has a structural function (it supports the weight of the entire rig), holds in the context of the function of lining/kerfing on an instrument? Sincere question. In my current thinking, it seems that the analogy is different. Not doubting the physics on the oil rig but instead wondering if the analogy is applicable to a musical instrument. Oil rig platforms don't have kerfs? Would the kerfs help to reduce the surface tension described in your diagram? Also this particular design is kerfed on opposite faces. Would such a design not further relieve the surface tension? In my mind, linings/kerfings are more of a glueing surface rather than a structural support for the top. If they were primarily structural support I would think we would all be using thick and solid laminated linings? But I do agree that they look nicer.

***Added
Timbuck I was writing response #9 to Chuck's question and then saw and read your reply. We must have been typing at the same time.

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It's not the weight thats the problem.. it's the expansion and contraction.

I any of these cases you've both pointed out I think you would be better of with solid linings. Why the need to confuse things to this extent? Things will get complicated enough when you actually start building. Build a few ukes using different styles of linings like most of us have and see if you can tell the difference. My bet is that you can't.

Moore Bettah Ukuleles said:

I any of these cases you've both pointed out I think you would be better of with solid linings. Why the need to confuse things to this extent? Things will get complicated enough when you actually start building. Build a few ukes using different styles of linings like most of us have and see if you can tell the difference. My bet is that you can't.

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Amen!
How did you make the cuts? Jointmaker Pro? I have lust in my heart for one of those to paraphrase Jimmy Carter.:drool:

Tarhead said:

Amen!
How did you make the cuts? Jointmaker Pro? I have lust in my heart for one of those to paraphrase Jimmy Carter.:drool:

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Yes cuts were made on the Jointmaker Pro. As soon as I saw the squiggle wood video the first thing I thought of was kerfing. Then I looked at one of their hand planes with the cove and I thought coved kerfing. They got me!!! Love the saw, not so much the price but I don't mind paying for quality and innovative ideas. Also plan on making rosettes, rosette logs, etc. The cove on the kerfing was cut using a router bit. I wish I had the hand plane. Next on the list

**Added**
But these cuts can be made on a bandsaw or tablesaw with the extra effort of flipping the piece 180 degrees. That could be done one by one for each kerf. That's how I do it on the Jointmaker. Or you could do one face using some kind of indexing pin and jig and then flip and reorient and do the kerfs on the other side. This style of kerfing is not limited to a particular tool. It could be made on many. It might be worth the experiment for those debating what kind of kerfing to build out of.

I don't use kerfed linings anymore because the way I build, solid linings work better and make the sides stiffer allowing the top plate to move more freely. After hundreds of ukes, I can tell the difference in the way they sound. It may not work for everybody and kerfed lingis are easier to install and take less time to make, but solid linings are my preference. I can really tell the difference on guitars, especially after the instrument is a few years old.

Thanks BlackBear. Do you laminate your linings to get additional thickness/stiffness? Is your design philosophy stiff side and stiff back? Or just trying to supplement and get a little additional stiffness with the solid linings? Just wondering how this little part fits into the whole system/philosophy. I've got solid linings on the soundboard of my current build and just installed the coved kerfings on the back. Thanks for sharing your experience.

Not trying to change your mind, I used solid linings too, just sharing my experience with this batch of kerfing, these squiggle wood kerfings (thin kerf and kerfs on opposing faces) seems like a win-win (compromise) for stiffness and ease of install. I'm talking about when they are 1/4" x 1/4" squares before any shape is carved into them. Because of the kerfs on opposing faces, they can be compressed together to the point where there is essentially no gap and almost look like a solid kerfing. This is not possible with traditional kerfings (kerfs on one face only). Not saying they are as stiff as solid linings just that they are probably the stiffest kerfed lining one could make. Maybe someone who has used the A4 kerfing (same design) can chime in on how stiff they get when glued to the sides. Food for thought. Thanks again Blackbear.

In effect, traditional kerfings are a combination of solid linings and individual tentalones. The best of both worlds IMO?

Moore Bettah Ukuleles said:

In effect, traditional kerfings are a combination of solid linings and individual tentalones. The best of both worlds IMO?

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Yes but the Squiggle Wood and A4 design is different. By traditional I was referring to how the kerfs are on only one face. The squiggle wood and A4 design have kerfs on opposite faces. Since Kevin Ryan got a patent on the A4 design I used "traditional" to refer to the kerfs on one face only. Chuck you're confusing me more...lol...with tentalones. Apologies if I was using common language for terms that had long standing definitions. But there is a design distinction between what I termed "traditional" (kerf on one face), whether it be rectangular, triangular, reverse kerfed or any other shape. If these linings are cut to a particular length they cannot be shortened or elongated by pulling on them. The A4 and squiggle wood can be elongated by pulling on both ends. They can also be compressed. The tentalones on a traditional kerfed lining, kerf on one face, cannot be pushed together because they are attached, by design, to the solid lining. So if the traditional linings are the best of both worlds, I think Kevin Ryan would say the A4 design is the best of 4 worlds

Not trying to say one is better but just point out the differences in design which allow for different capabilities. You gotta play with the stuff. It's hard to see what it can do just by looking at the pictures. It will blow your mind...just like the saw.

Real traditional corner bracing is done by gluing small individual blocks of wood, called "tentalones", to the joint. You don't see this much anymore as most modern builders favor the speed and ease of installing strip kerning (or "kerfed Linings"), which in effect is simply individual tentalones attached to a solid lining.