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I'm planning a OO size steel string guitar. I've built 20 spruce topped guitars to date, but never one with a cedar top. What thickness would you recommend for this top, and do you brace cedar tops with spruce bracing?

Hi Ken,

The general recommendations are to make your cedar tops 20% thicker than a spruce top. Spruce is the best brace wood to use no matter what species top you are using. Cedar dents very easily so keeping your work area clean is extra important. When you are ready to install your bridge, be careful not to cut any fibers of the top when you do your masking or finish removal. The fibers will peel off and you'll be regluing your bridge.

Steve

Steven pretty well covered it. Cedar bracing would be lighter weight than spruce, but would creep faster due to the low strength, and split more easily from accidental impacts. Spruce is pretty much the perfect balance of stiffness, density, strength and toughness for bracing.

Adding carbon fiber like Trevor Gore's falcate style makes it even more creep resistant. Laminating higher strength wood in the center like purpleheart probably would as well, though that has a weight penalty. But solid spruce is already very good.

I/ve used 1/4 sawn WRC for bracing stock . depending on your top it needs to be at least 10% taller in height.Being from BC WRC varies a lot in density, 25 lines per inch would make a vy light an stiff brace adding CF would make it stiffer/ tighter .I/m experimenting making falcate braces using WRC

Cedar and spruce both track basically along the same line of Young's modulus vs density. That means if you can track thicknesses and densities of spruce which worked well for you - you can thickness the cedar proportionally. You could also deflection test and thickness to get it about right. As with spruce - there's huge variation within cedar. Test and adjust accordingly.

I have some spruce that is incredibly light and I have some that's about like hard maple. same for cedar. Same for redwood. I have some cedar the same density as spruce - I will thickness it the same.

Thanks
John

As John says, Young's modulus along the grain pretty well tracks density in all softwoods in the same way. I the tests that I've done, about 2/3 of the samples will fall within 10% of the expected Young's modulus based on density. The outliers tend to be pieces with a lot of what is sometimes called 'compression grain': heavy latewood lines that add more density than stiffness. These will be less stiff than they 'ought' to be for their density. I have not seen much of that in cedar, but it's common in redwood.