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I use quartersawn spruce side reinforcements strips between my kerfing. The only function of these is to stop a crack from traveling, if a crack occurs. On my current build, the wood movement of that construction areas was bothering me.

If the sides expand, they do so, mostly, in the width. The side sticks will not expand at the same rate in that direction. Since the side strips are precisely fitted between the top and bottom kerfing, they will PREVENT the sides from expanding. Restricting contraction/ expansion is a classic furniture construction method that causes wood to crack. The way I learned to install side reinforcement strips could CAUSE cracks!

Today I have feathered all the ends of the side reinforcements to zero at the kerfing. Anyone have a different perspective? I expect a lot of you use cloth to reinforce the sides.

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Measure Twice,

Karl Borum

I usually use cloth unless the sides need more reinforcement then I use wood that spans the entire side. I understand your reasoning but so far I have not had a problem. I do them like this:

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Steve Smith
"Music is what feelings sound like"

I too use wood strips cross grained but I'm no expert. I have not had any side cracks but my sample size with these cross grain strips is small and none of them have ever been exposed to dangerously low RH. I tend to feel that the relatively narrow width of the sides is not enough to cause them to pull themselves apart unless they get really dry. I feel like an 15 inch wide back plate would be a different story. I could be wrong here. With that in mind, I'll say what I do, but leave it up to the reader to decide based on all the experienced replies we will likely see here.

I do worry about side reinforcements ending at the lining as all the stress would be concentrated there and a crack could end up running the whole length of the side between the reinforcements and the linings. With that in mind my reinforcements run under the linings. Feathering them out will reduce this stress as well but I suppose you still have that narrow line of unreinforced side all along the lining for a crack to follow.

I put my linings in first all the way across the width of the side. My strips are roughly as thick as the side material. Next, I glue in segments of lining strips (the same thickness as the reinforcements) that go from one reinforcement to the next (or the heel or tail block). Two additional thicknesses of linings get laminated over that going from block to block. When it is all said and done, the linings are "solid" (really a 3 piece lamination) that house the reinforcement strips.

I hope that makes sense.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Yup, either full length or feather to zero. I built this flamenco some 15 years ago with straight side braces and you can see where it is stressed right at the tip of the side brace and the lining. Learned the hard way.

I usually only use side reinforcements if I need to flatten ripple sides like ribbon sapele. I just don’t run them edge to edge but stop short a little way each end, although I’ve certainly run them full length before with no problems so far…

If you think about it, what's the difference between a full width side brace and a full width back brace? We don't worry about the back braces and I'm not real worried about the side braces.

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Steve Smith
"Music is what feelings sound like"

In my mind, the difference is that the back brace has some dome built into it. In order for the back to pull itself open, it first would need to shrink enough to flatten out the dome, them shrink some more. Sides are relatively flat
from plate to plate. I imagine that if the side wood for really wet, it could bulge and bend the reinforcement brace and if it got too dry, I could break the glue line to the reinforcement or crack. I just don't feel like the height of the side is enough room for cross grain movement to break the side.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

A good point although I was thinking of the different shrink rates of the two cross-grain pieces of wood which would be the same in either case. It's not a big deal for me since I only use wood side braces when the wood doesn't want to stay flat so I've only got 3 or 4 out there but have had no issues so far.

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Steve Smith
"Music is what feelings sound like"

I was told by one of the instrument conservators from the Met in NY that wood side strips must be inletted under the liners to avoid the problem that Bryan Bear pointed out of producing a stress riser that causes a crack in the hardest place to fix.

I always wondered about cross grain shrinkage of the sides causing cracks, and several years ago I go what seems to be the answer: they can. I had two imported guitars from the same maker come in one winter with side cracks in the flat part of the lower bout where they had used wood side fillets. These were deep boxes, made of a soft wood related to koa. The cracks were more or less in the center of the side, and ran across the reinforcing fillet.

I have found that cloth side strips work well in stopping cracks from running along the side. In measurements of sample pieces with various side tape materials and glues I found that the tapes increase the force needed to break the samples significantly, and I've seen instances where guitars I've used them on have taken hits; one sufficient to punch a hole in the side. The crack runs to the next tape and stops, and since it doesn't shift its an easy fix.

I’ve been doing this for side braces for a couple of decades. So far, no problems that I know of.

I have definitely seen back braces pop off bindings before. Still do it the usual way mind you…

The first several guitars I built had the side braces butted to the linings. Then I learned on this forum that that approach is not optimal. All of those guitars are fine to this day, but since then, I've done side braces that are tapered down to nothing at the linings or side braces that run almost the full width of the sides under the linings. More recently, I've only used side braces to flatten a side if needed and for those the side braces extended under the linings.

Last year, I ran across some examples of builders, including Linda Manzer, who extend the side brace ends over the kerfed linings. It seems that this approach avoids a stress riser from having a side brace just stop at the linings or having a weak spot with tapered-to-nothing side brace ends. The installation is also simpler than letting in the side braces under the lining. I put in side braces this way on the instrument I'm building now just to try it out. The brace ends were fitted to the shape of the kerfed lining and the brace ends are glued onto the linings as well as the braces being glued to the sides.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

I think that whack the guitar took that left a dent in the binding played a role here...

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Peter Havriluk

Crap, I forgot about this as was building my second body. Too late to do anything other than butt joint them. I used cloth on my first and just glued the linings over them. What's the best fix without cutting all of the spots where they go. That would be a real pain.

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Hutch

Get the heck off the couch and go build a guitar!!!!

Gerard Gilet does this, or did it anyhow. He gave me a spare jig that was once used in his shop to shape the brace ends to fit over reverse kerfing. I do side braces differently these days but with a decent jig the over-kerfing approach is quick and a sound design to boot.


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To my eye, that just looks like a butt joint which is not what you described.

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Hutch

Get the heck off the couch and go build a guitar!!!!

I used tapes, cloth Karl like Martin has for over 100 years and good on you for anticipating what each of the components are going to do with RH changes. Nice to see someone thinking about how their work will survive and I agree with your conclusions from your analysis.

Tapes are time tested for well over 100 years and they work very well. Their only function is to stop a crack from traveling beyond the tape and they do that very well. If side stiffening is needed there is no reason why a hybrid approach could not be utilized and someone could use both. But you have to allow for expansion and contraction as Peter found out. Hat's off to Peter for helping us all learn and being honest about his learning curve, that's very nice to see again on the OLF.

I attached mine with watered down Titebond Original but others use HHG and that's more traditional as well.

Nice to see people getting the basics down before trying to reinvent the wheel when there is very little that someone else has not tired and often failed at in Lutherie.

This is our experience too and as the eyes of what doesn't work in the repair business we have commonly seen side supports become loose and/or fall off especially after an impact or from drying out. We have never seen a side tape come off.

When I ran the strength tests I used two different types of tape: cotton/polyester bias tapes, and some nylon twill tape that was sent to me to try out. The wood samples were supported on a couple of dowels with the tape side down and loaded by sliding a can full of marbles along a lever until the sample failed, which allowed for calculating the load it took. One interesting thing was that the cotton/poly tapes tended to break when the wood did, while the nylon tapes peeled loose, so they were no longer supporting the wood, which then broke. Both failed at about the same pressure, which tended to be around 40%-50% higher than bare wood samples. I have seen old Martins with side cracks through the linen tapes, and some folks cite this as evidence that the tapes don't work. However, there's no way to know how much force it took to break them.

I use hide glue to apply my tapes. Partly this is because it's easier than using Titebond, but also, in my trials, the hide glue seemed to be a bit stronger. This could cause a problem in the long term, since hide glue breaks down over time when its exposed to air. You will often see old mandolins with reinforcement glued to the inside of the bowl where the cloth or paper is flapping loose because the glue broke down. To guard against that I put several coats of shellac on my side tapes; enough to give a glossy surface. We'll find out in fifty or seventy-five years whether it worked...

I've done side reinforcements a number of different ways but have settled on wood veneer run under the linings. I think it is important to glue them in under the the right relative humidity with the wood fully acclimatized to it. Similar to cross grain bracing, I think this gives it the best shot to survive humidity swings.

Could be, I'll never know.

I only use side strips on guitars with very thin sides now, which I rarely make, so I pretty much don't bother with them any more.

Trevor Gore's book notes that he puts a bow in the sides (the middle bows outward) as he likes the look of it better. I have also considered that, like the top and pack, it gives it some room to move. However, most people take the dome out of the top and flatten the upper bout (for neck setting) and heavily brace it, thereby restricting its movement.

Kwa?

Could you leave a reference page for that? There’s still lots in those books for me to absorb…

It’s in the build volume, 10-13 and 10-14 shows the clamping caul used to impart the outward bow. I do mine like this. The amount of outward bow is very small and I think more of a hedge against future concavity of the sides.


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Thanks!