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So far I've worked only with Spruces - Sitka, Adirondack, and Lutz from multiple sources. First time using Cedar or Doug Fir.

Some interesting observations:

Thicknessed them both this morning and stopped at the same point (.113) just to take some notes.

Cedar - stiffness is almost dead even in both directions. In fact, just going by feel, it appears to be just slightly stiffer ACROSS the grain. Huh? That's a first!

Also on the cedar - MAN this stuff is brittle! Ridiculously so. While flexing the top during thickinessing (and not getting crazy with it) the top snapped in half midway of one of the plates. I reglued it, but the top has cracked twice since then from the end with normal handling - just by picking up the top from the end of plate. Man, I've gotta handle this stuff with kid gloves!

Doug Fir - extremely stiff along the grain and quite flexible across the grain. In fact, the cedar at this point is considerably stiffer across the grain and much looser with the grain. I still feel like I need to reduce the long grain stiffness of this piece a good bit, which may make it pretty floppy across the grain. Will need to modify my bracing accordingly.

Partly I just wanted to share these observation, but they left me with a couple of questions, too:

1) How typical are these results?

2) How would you approach the bracing and top thickness based on these results?

The Cedar is for a Koa OM I'm working on and the Doug Fir is for a Mahogany dread. I'm looking for a good all-around players' OM out of the Cedar and hoping for some good bluegrass punch out of the dread. The dread will likely be forward shifted and scalloped, but I may reconsider the bracing based on how floppy it winds up across the grain. I know the typical advice given on Cedar is to add about 10% thickness over Spruce.

The cedar is so ridiculously crack prone, I'm even considering my first lattice for the lower bout. That's a lot of new variables for me on one guitar.

I haven't yet set up a deflection rig for testing stiffness and strictly work by feel, but this has me seriously thinking about it!

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Wes McMillian
Santo, TX
http://www.wesmcmillian.com

Hmmm.....kinda surprised to get nothing at all here. Oh, well, I'll keep plugging along and learning the old fashioned way like I usually do. Already made up a lower bout lattice for the cedar. I'll thin the Doug Fir until the long grain stiffness gets where I want it, then try to brace up the cross grain. We'll see what happens.

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Wes McMillian
Santo, TX
http://www.wesmcmillian.com

I've seen some postings (from Alan Carruth, I believe) which I seem to remember, provided a correlation between stiffness and density of the tonewood, regardless of species. Alan, forgive me if I'm getting this wrong.

What this tells me is that you should do some measurements on density - really easy to do if you haven't before. Weigh them with an accurate kitchen scale, then take the width, thickness and length, then do the math to get grams per volume (I use grams per cubic inch, which works for me - others have, understandably laughed about the apples and oranges of that measurement.)

Then do some deflection tests on the tops. At which point of thickness do they "deflect" under a fixed weight? You can go by what you "feel" is appropriate stiffness for each, then take the measurements. $10 says the cedar will be thicker than the Doug Fir at a given constant deflection (assuming equal width for the backs).

For what it's worth, I haven't worked with Doug Fir before - although I have some nicely quartered planks that I'm saving for a rainy day project. The samples I have are far denser than the other tops I have. Yeah, I know, every piece of wood is different (even from the same tree). nevertheless, here is some data that I have....your results may vary

Sitka Spruce - from 6.6 to 7.9 g/cu inch
Lutz Spruce - from Shane Neifer - 6.0 - 6.6 g/cu inch
Sinker Redwood - 6.9
Adirondack - 6.8 - 8.0
Euro - 6.4 - 7.1
Englemann - 6.0 - 6.1
Cedar - 5.0 - 6.3
Doug fir - 8.0 grams per cubic inch

And, as one might expect, the cedar I worked with, which is far less dense than Doug Fir, (and the least dense of all these samples) was VERY fragile. I had fewer challenges with the cracking that you're describing, but it dents extremely easily. I'd expect the Doug Fir to be on the other end of the spectrum.

So, at the end of the day, unless your samples are extreme examples of their species, for same guitar size and style, and aiming for a target of responsiveness of the top, you'd expect the cedar to be a thicker top than spruce, and the Doug Fir to be a thinner top than most spruces.

I would say FIR and similar HEMLOCK has great structure depending on quarter cut. Most fir growth rings are thick compared to other bracewood. So..The tighter the growth ring the better. FIR is Definitely heavier and quite stiff. Bracing can be thinned to achieve the same structure as other softer bracewood. However....because of the stiffness....it is not as elastic and is brittle and gets even more brittle in time. I can see the lack of elasticity as being a possible issue with cracks in back due to lack of expansion /contraction fights between bracing and back and bracing failure down the road. I would say...More suitable for smaller body guitars.

Just my opinion here.

Kent

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