side stiffners

[Clay Schaeffer]

In another topic on the forum I read - "Lately I have been using side braces full height on the sides and quite thick, in theory that will make the sides stiffer".
Although I can see some benefits from this I am wondering if anyone has encountered any problems with it. Sides are relatively narrow, but under extremely low humidity conditions could the sides being restrained by thick side braces cause them to crack? Has anyone experienced this?

[Bryan Bear]

That's a good question and I'd like to hear peoples thoughts and real world experience (there might not be a lot of data points out there though). I wondered the same thing. I use cross grain strips full height about the same thickness of the sides. About 5 years ago I thought using thicker reinforcements tapered down to fit under the second layer of my laminated linings would be better. I made two instruments like this before I decided to stop. My thought process was similar to yours. I worried that the added stiffness of the reinforcements might be too much resistance to movement (when extremely dry) for the sides to handle causing them to split along the grain.

In reality, this is likely a concern with solid reinforcements in general but I feel like the thinner stock will be more able to bend with the side causing the side to go a little concave when dry. I don't know if that is how it would really work though given the rigidity that comes from the curves in the sides.

At any rate, I have two instruments out there with thicker side reinforcements. Neither have cracked in the 5 years they have existed. But. . . that's not a ton of evidence that it is okay. One of them is a mandolinetto so the sides are only about 2.5 inches deep. That greatly reduces the amount of shrinkage that would occur across the width of the side. I will say that it had been exposed to some pretty dry conditions for a couple months. The other is an L-00. This one is not in my possession but I see it from time to time. It doesn't see a lot of humidity control. The sides are black walnut so they may be less prone to movement than other side woods.

[Trevor Gore]

I've seen guitars move so much under humidity changes that back braces have been blown off and, in one extreme case of over humidification, where the back bindings had blown off at the butt end because the back panel had grown nearly 2mm along its length. That same guitar had evidence of gross under humidification, too. That's Australia for you. However the sides, with wooden splints, had survived, without cracks or detachments. I can think of two reasons for that, but can't prove either. The first is that the sides get severely heat treated when being bent and this "extreme seasoning" reduces the propensity to move. Greater stability is one of the objectives of heat treating wood (like the current trend we see in torrefication) and the phenomenon is well known. The second is that sides are a lot narrower than backs, so the distance moved is much smaller. I can't remember ever seeing a guitar with side damage that wasn't obviously some sort of direct or secondary impact damage.

So I think there are many other potential problems to worry about first.

[Arnt Rian]

sides are a lot narrower than backs, so the distance moved is much smaller.

This, I think, is the main reason sides usually don't crack from dehydration, even if the back does.

I sometimes use thicker side reinforcement braces to stiffen squirrely sides, but I make sure they terminate below the top surface of the side, the idea being that even if the sides shrink excessively, the side braces won't start pushing against the top and back. At least I like to extend them further up into the linings, to avoid a weak point between the two, which can lead to a crack.

I remember getting an old basket case guitar to fix up once, it had all sorts of cracks and problems all over. I do remember the side braces and end blocks, with the grain oriented opposite of the sides, were at least a couple of mm longer than the side's width, causing the plates to separate from the side. The glue had also partially slipped from the braces and blocks. I'm sure extreme dehydration and poor material / design choice were the main causes, but it was also a reminder avoid, if possible, structures that resist the wood's movement. That's why I sometimes skip side reinforcements, if the wood seems sturdy, the sides are narrow, and the instrument's outline is nice and curvy (no 'dreadnought style' flat areas).

[Christ Kacoyannakis]

Interesting topic. There are lots of different ways of doing this that I have heard about. Some makers use full side thickness braces, under the theory that if they stop them at the linings, there will be a stress point at the juncture. Others just use a brace that goes from lining to lining. A third group inlets the side brace into the lining (Tom Bills), but he is also using very stiff linings that are solid laminations (very cool!). Some don't even use side braces. I have also heard of makers who laminate the sides out of several layers of wood to make them stiffer. So, what I am gathering is that stiff sides are good, and that making them overly stiff does not hurt tone. Is this correct?

[Alan Carruth]

I have seen two guitars with side cracks that I thought could be attributed to side braces. Both were imports, with deep sides made of some sort of soft wood (one or another acacia?). They had cracks along the side that ran across the side braces, which had been put in on the straight part below the waist. The cracks showed up in late winter, which is the usual time of year for low humidity issues here in New England.