Side/rib reinforcements- when/where/how many?

[Charlie Schultz]

I got an e-mail from StewMac advertising their brace repair jack and the picture reminded me of a question I've always had- it shows an inside shot of a guitar that has several side braces and I wondered when and why they get used. I've seen one or two GAL plans that showed them.

[Bob Gramann]

I use side braces in the belief that they may prevent or stop the propagation of cracks in the side in the event of a blow. I use scraps from the top plate and make them about as small as I can handle. I attach with a pva glue so there will be a little flexibility in the glue joint. I place them roughly every 4 inches and (unlike the StewMac photo) let them into the linings so there isn't a convenient place for a crack to start. I have no empirical data to validate their necessity. So far, (around 100 guitars) I haven't a side crack with or without the side braces.

[Bryan Bear]

I'm certainly no expert on them but I'll share my thoughts and what I do anyway.

I use them to hopefully stop any cracks from propagating. I've not had any cracks so who knows if it is working <g>. Like Bob, I run them under the linings so cracks cant's spread from right under the linings. I don't really have a set position for them and am frankly not all that careful about where I put them. Since they run the full width of the side, I make sure they don't pass under any braces that will get tucked into the lining (upper x arms. . .). I also try to make sure I support the flatter curves more as it seems to me that the curved areas are naturally stronger because of the curve; that could be fallacy on my part. Often, the placement is not totally symmetrical since I am just placing them as I go based on feel and whim (once the top and back is on, no one notices ).

I use laminated linings with 3 strips of roughly the same thickness as my sides. My side reinforcements are made from one strip. the first layer of lining is place between the reinforcements, both surfaces are even because the thickness is the same. Then I laminate the other two layers of lining over the first and the tops/bottoms of the side reinforcements. Seems to work okay for me.

[Alan Carruth]

When I was taking my violin making lessons we used to get instruction from a woman who worked in the instrument restoration department at the Met in NY. She said that it's imperative to inlet side braces if you use them. If they're not inletted into the liners there is a stress riser at the juncture between the brace and the liner, and that's where the side will crack, just where it's hardest to fix.

One of the reasons I never took up using wood side fillets was the worry that they don't shrink in the same way the sides do with lower humidity. If the side tried to get narrower and the wood brace didn't get shorter it seemed to me that could cause a crack. A few years ago I actually saw a couple of guitars with just that problem. They were Australian imports, with some sort of soft local wood for the B&S, and a deep body. They had cracks in the sides in the area just below the waist which actually ran across the wood side braces.

I've been using cloth tapes for a long time to help stop cracks. I put them on before I glue on the liners, which go over the ends of the tapes. The tapes don't seem to interfere with the gluing of the liners at all. Aside from the fact that Strad used side tapes in his 'cellos, I've done some testing to validate them on my own. My experiments suggest that the tapes add appreciably to the force it takes to crack a side. The best combination of the ones I tested was cotton-polyester bias selvege tape, glued on with hot hide glue. I have also seen instances where a guitar with tapes got a crack in the side, and it stopped at the next tape.

Tapes are not as strong as wood fillets, of course, and won't protect against real abuse as well as wood braces would. The other main objection to them is that the glue tends to break down with age, allowing them to come loose. I've tried to cover that base by putting shellac over the tapes after the liners are on to keep the air away from them. I'll find out in 75 years or so whether that worked.

[Bryan Bear]

I'll find out in 75 years or so whether that worked.

Make sure you update this thread when you do


I have thought about the differential shrinkage you mention and sometimes worry about it. Obviously, it is a real concern and I suppose the side wood, how it is cut, depth and RH while building would all play a role. So far, I have not made any instruments with really deep sides. Probably less than 4.5" at the tail. I wonder just how much shrinkage a 4.5" wide quarter sawn board will see and how dry does it have to get be problematic. If the linings are put in at relatively low RH, I would think it would have to dry out quite a bit to pull itself apart. Woods that move more, are flat sawn and/or are more split prone would increase the concern (I would guess).

It makes sense that you saw these cracks in the waist. If a rim gets dryer than it was when it was made, the crossgrain strips would make the sides want to go concave. The tight curve of the waist would be the most difficult part of the rim to distort in that direction.

I'm wondering if I have just been lucky so far. Or maybe the fact that I tend to keep them near the flats where it is easiest for the side to cup has saved me.

On a related note, I hear about people using high quality plywood for tail blocks. I wonder if this same concern applies. The tail would be the widest part of the side and should see the most shrinkage. Perhaps the interruption of the end wedge or the thickness of the block saves them there.

[Arnt Rian]

I generally don't use them, other than to stiffen the ribs of some instruments. For example, sometimes I use them on the flattish section below the rib on dreads, to avoid cracks caused by a key-chain or similar in a player's pocket, or if the instrument has particularly flimsy sides. I don't like them mostly because I think its easier to make a good repair without them, if the sides should crack.

[Matt Cushman]

It may depend on the type wood the sides are made from. For Maple a full width side brace is a good idea to help prevent warping or cracking. I have used some Maple for sides that had to be braced. The only reason I used it for sides was because it was so nicely figured.

[Alan Carruth]

"It makes sense that you saw these cracks in the waist. "

Actually the side fillets were in the 'flat' are below the waist, and that's where the cracks were.

[Bryan Bear]

Shows what I know

[Todd Stock]

Fabric...bias cut cotton-poly tape that is applied before the ribs are profiled and linings go in. For guitar bodies with large, flat areas like dreadnoughts, I use spruce or mahogany side supports in that area only, although even fabric will prevent key cracks. FWIW, I use hot hide for the glue, then shellac once linings in.

[Trevor Gore]

They were Australian imports, with some sort of soft local wood for the B&S,...

I didn't think we did soft!

Most of the stuff around here you can't drive masonry nails into once it's dry!

[Alan Carruth]

Trevor Gore wrote:
"I didn't think we did soft!"

OK: the impression I was given was that it was 'local' wood, but perhaps it was not. It was soft, though, and not well quartered.

[Simon Magennis]

...
I've been using cloth tapes for a long time to help stop cracks. I put them on before I glue on the liners, which go over the ends of the tapes. ...

I took up this trick from Alan after reading about it here. I am not as precise about how I put them on and generally do it just before I close up the box as I simply forget to put them in before the liners. I usually put a few wooden ones in as well.

[Steven Smith]

I've tried using both wood side braces and cloth tape. I've gone to the cloth tape because its just a lot easier to install. I use the bias tape, HHG, and shellac method Alan discussed and install them at about 4 or 5 inch intervals. I don't have enough guitars and certainly none are old enough to have a clue if this will be a good thing. Perhaps my grand kids can let you guys know when they retire .

[Todd Stock]

The problem with side supports is that when installed incorrectly, they will do a good job of promoting cracked sides...supports need to ideally span the entire side, and as a minimum taper or pocket into the lining to avoid creating abrupt changes in cross-grain stiffness. Fabric is easier to apply, is a bit lighter, and may look a little more traditional than wood, but they do not add as much crossgrain stiffness. Wood requires some clever joinery, but adds enough crossgrain strength and stiffness to address things like key cracks on dreads. Best of both is cloth in 'curvy' areas and wood where the additional weight and complexity of installation is warranted, such as the flat areas of a dreadnought side.

Alan Carruth did some very good work examining fabrics a while back...IMS, he suggested cotton/poly bias-cut cloth as a good compromise with regard to contribution to stiffness, resistance to peel, and ease of use...please correct me, Alan, if I've misstated the work. When I do fabric side supports, I lay out and apply tape dams to work against...once saturated with hide, the tapes can be stretched or scrunched to line up on both edges, and then worked with a paper towel wetted with hot water to get rid of excess glue. A coat of shellac seals the hide against biological attack should the guitar remain in a damp environment for a prolonged period.

[Todd Stock]

Tape or wood color/texture can create some visual interest as well...for ported guitars where the owner will gaze lovingly on interior appointments for hours on end...

[Alan Carruth]

The experiments I did compared two kinds of tape and two adhesives. Somebody had sent me some nylon twill tape, and I wanted to compare it with the cotton/poly stuff I had been using. The nylon is certainly stronger material, and would look neater, but I wasn't sure how it would glue. I also decided to see whether Titebond or hot hide glue was better.

I cut slips of wood the same size from failed sides, of several different kinds of wood. I made several samples with each combination of tape and glue from each kind of wood, and also kept out a couple of samples of each wood with no tape for control. The tapes were applied as I would on a guitar, but with no liners. They were glued on, and , when the glue dried, I gave them a few seal coats of shellac. I made up a simple lever rig that would load the samples, using a can of marbles that I could slide along the lever until the sample broke. the distance out from the pivot, and the tare of the lever, gave a reading of the load imposed. The wood samples were supported tape side down on two dowels an inch apart, with the dowels running along the grain. A dowel on top, parallel to those and in the center of the span, transmitted the load from the lever.

What I found was that the tapes increased the force it took to break the samples by about 50%, more or less. The bias tapes tended to break when the wood did, while the nylon tapes were more likely to peel off without breaking. The bias tapes withstood a bit more of a load than the nylon ones did. Hide glue was a bit stronger than Titebond in this application,which is nice since it's easier to put the tapes on with hide glue.

I've had a couple of guitars with the tapes that have taken knocks that caused cracks. The cracks tend to run up to the next tape and stop. This makes for a MUCH easier repair than the worst case, where the crack runs from one end of the side to the other. Even a more 'normal' crack, say five or six inches long in the lower bout, tends to get out of line a bit, and can be tough to do a good repair on, so anything that keeps the crack short is a good thing in my book.

[Randolph Rhett]

Just so I understand, by "tape" you mean just strips of cloth you cut and that you saturate with hide glue? Or are we talking some kind of manufactured store bought product? If the later, could you provide a link to the product you are referring to?

[Todd Stock]

Wright cotton/poly bias tape in Seal Brown or Mocha Brown is what I use...a couple bucks at Walmart or a fabric/sewing supplies store...I iron the stuff to flatten it ou, trim to 5" lengths, then use a rotary cutter to cut to final width (about 5/8" - 11/16"). Martin tried a PSA-type tape to save labor and it did not turn out well.

I trimmed a couple shots from the photo essay...here in the opening shot...the tape dams are applied, the dry tapes are laid in a bed of fresh, hot glue, then patted/screed with paper towel soaked with hot water...pat the tape down after the excess glue is dry, pull blue tape off, and carefully clean any residual glue off the adjacent wood surfaces.

Once the dried/now hardened tape is dry, lightly sand edges with 320 and glue in linings over the tape. When all is dry and profiled, apply a coat of 1 lb cut shellac to protect the surface of the tape...if you get a little sloppy, just use a razor blade scraper to clean up any errant shellac. The single shot of the completed rim shows typical look of Seal brown tapes on lighter side woods...also an option to use whatever color works...black or tan would be decent options. Look inside vintage Martins and some other quality brands and you'll see essentially the same approach, although usually a cotton sateen, silk, or similar material used. All this takes far less time to do than talk about.

Also...once I have a tape layout done for a particular body, I take a 1" wide strip of maple veneer and transfer the locations with any notes...tape the ends with blue tape and punch a hanging hole...usually put the full side layout (including sound port location, which gets wider tapes over the mahogany transition ramps to the side doublers) on one side and the cut side layout on the other (if they vary...they usually do).

[Randolph Rhett]

Never heard of the stuff before. Thanks!