To Popsicle Brace or Not To Popsicle Brace

[SColumbusSt]

Greetings,

I'm building a 14 fret 00 from a kit and trying to make it as accurate to a 1930's Martin as possible. I have a wonderful drawing of a 1938 00-18 and have emulated the top/back thickness and brace locations as carefully as I can. I'm done gluing on the bracing and about to start shaping the braces but am wondering if I should glue on a popsicle brace even though it is not period accurate.

From my limited experience building and tapping around the top the area near the neck is pretty acoustically inert. From my decades of experience as a guitar nerd I know fingerboard cracks are known to happen on 30's Martins and many repair people have added popsicle braces over the years to original guitars to shore up that area. I also know some repair people specialize in removing popsicle braces from guitars so clearly there is a line of thought that they impede the vibrations of the guitar.

The neck block on my guitar has a modern foot extension (which along with a truss rod are the two "modern" features of the guitar). Is that enough to strengthen the top in that area or should I also add a popsicle brace? Thanks for any and all opinions.

Keith

[Talldad]

Most acoustic guitars have a huge brace just north of the sound hole going left to right. It’s commonly thought that this brace prevents energy from dissipating away from the rest of the soundboard, it acts as a big node. If you strum a guitar and place your hand on that area above you should feel little or no vibrations on your hand.

The volume of air in that part of the guitar may affect its resonant qualities but the spruce board? Not really.

[Zigeuner]

The so-called Popsicle Brace does add strength to that area of a guitar. Some folks do remove them in an attempt to gain a better sound. The jury is still out on that.

[JonWint]

Most builders don't use the modern block with the foot (I cut them off the modern blocks). Instead of the upper plate brace (aka popsicle) use trapezoidal veneers to at least double the shear strength of the top at the outside edges of the block. That scheme gives better resistance against shear failure from block tilting. The extra veneer connects the neck block directly to the upper transverse brace.

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[John Arnold]

Another vote for the trapezoid brace, which I make the same width as the neck block on the upper edge, and 4" wide at the lower edge. Grain in the trapezoid brace should be parallel to the top grain, or slightly skewed. The angled edges prevent a stress riser, and bridge across the fingerboard edge to mitigate the stress there. Fitting it tightly between the neck block and the upper transverse brace will help keep the neck block from shifting, too.
The two-part trapezoid pictured is normally done to allow for truss rod adjustment.

[SColumbusSt]

Thanks to all. The trapezoidal brace looks like the way to go. About how thick is the brace?

Keith

[John Arnold]

I usually make them about 0.150" thick. Quartered red spruce, usually.

[redir]

I like the A-Bracing now and pretty much use it on all models. The A frame I make is 1/4in thick bracing.

[Rudy4]

The upper transverse brace (directly above the sound hole) often does little to prevent the dreaded "top block crack" that often appears directly along the top block on both sides. The true "popsicle brace" is much wider than the top block width and has angled or rounded ends to prevent stress riser fractures of the top.

There's very little contribution to sound from this area and I would not personally build an instrument without one. The trapazoid brace is a half attempt to address the problems from stress along the top block. It's not bad, but a true popsicle brace is better IMHO.

Wood guitars move. Attempting to make them into a more unified and "monolithic" structure may or may not work. There's a lot of years of practical data that demonstrates what works, not so much with flying buttress bracing and other "unique" marketing strategies.

[John Arnold]

I have seen guitars with popsicle braces fail. I have yet to see one fail with the trapezoid brace. The popsicle brace is installed cross-grain, and that joint has a tendency to creep, especially if overheated.

[Alan Carruth]

I've been using an A-brace, similar to redir's, for ~25 years. I have direct evidence that it can resist/prevent the neck shifting inward from drops that might have caused the top to crack along the sides of the fingerboard. I inlet the upper ends of the A-braces into the neck block. I also use a doubler around the sound hole and within the perimeter of the braces, about .1" thick and with it's grain slightly angled across that of the top (3-5 degrees). The lower ends of the 'A' are trimmed down to the height of the doubler thickness, and inlet into the upper arms of the X brace with triangular inlets, to help keep them from peeling up.

I have seen more failures of popsicle stick braces when yellow or white glue is used, due to creep in the glue line. I use hide glue for bracing these days, and see less evidence of creep.

[Rudy4]

Anyone concerned about cross grain installation of the popsicle brace probably should re-think the upper transverse brace as well as the bridge plate, which are both traditionally cross grain and don't generally cause any problem.

[redir]

Originally Posted by Alan Carruth

I've been using an A-brace, similar to redir's, for ~25 years. I have direct evidence that it can resist/prevent the neck shifting inward from drops that might have caused the top to crack along the sides of the fingerboard. I inlet the upper ends of the A-braces into the neck block. I also use a doubler around the sound hole and within the perimeter of the braces, about .1" thick and with it's grain slightly angled across that of the top (3-5 degrees). The lower ends of the 'A' are trimmed down to the height of the doubler thickness, and inlet into the upper arms of the X brace with triangular inlets, to help keep them from peeling up.

I have seen more failures of popsicle stick braces when yellow or white glue is used, due to creep in the glue line. I use hide glue for bracing these days, and see less evidence of creep.

I have been thinking about modifying my design to inlet the braces. I currently just butt them up. Do you have a jig for that or do you just kind of mark it out and chisel it away? And how far do you inlet?

[Alan Carruth]

I just mark and chisel. I don't inlet them far, less than 1/2": tight is more important then deep.