Question About Sitka

[Eric Knapp]

Hello, all.

I have two boards of Sitka spruce. One I've had for close to 40 years and the other I got recently. I'm wondering which board would you pick first for guitar tops.

The old board has about 24 rings per inch.

The new board has close to 60 rings per inch.

The new board looks pretty nice. Here's a photo of the silk before I surfaced the board at all.

What say you, good sages? The new board was 16 feet long, a full 1" thick, and 9 1/4" wide.

Thanks,

-Eric

[Barry Daniels]

The grain in the second board is more even than the first one which shows some variability in growing conditions. Looks like there were a couple of periods of drought years in the first board. Have you bonked on the boards to see how resonant they are?

[Bob Gramann]

I would flex them across the grain. The stiffer one cross-grain I would use on a larger body. The floppier one on a smaller body. 60 rpi is pretty impressive, but how it works still depends o the individual board. Any board that’s floppy I save for when I’m making a narrow body guitar where the flexibility cross grain matters less.

[Eric Knapp]

The grain in the second board is more even than the first one which shows some variability in growing conditions. Looks like there were a couple of periods of drought years in the first board. Have you bonked on the boards to see how resonant they are?

The two guitars I'm working on now are from the first board. The tops seem quite resonant but I don't have a lot of experience tapping tops. We'll see how they turn out. The new board is 1" thick, can you get a sense of the resonance by bonking it?

-Eric

[Eric Knapp]

I would flex them across the grain. The stiffer one cross-grain I would use on a larger body. The floppier one on a smaller body. 60 rpi is pretty impressive, but how it works still depends o the individual board. Any board that’s floppy I save for when I’m making a narrow body guitar where the flexibility cross grain matters less.

I will have to resaw a sample and see. Spruce seems stiffer in general than the cedar and redwood I've used so far. The redwood in particular is really floppy.

-Eric

[Barry Daniels]

Yes you can bonk a 1" board but you need something larger to do the bonking, like a large rubber mallet. I read that the tonewood cutters in germany used to bonk standing spruce trees with a sledge hammer.

[Alan Carruth]

If the boards are rectangular and reasonably uniform in thickness you can test the material properties. You'll need to measure the size of the board, get the weight, find the pitches of the long-grain and cross grain fundamental modes. Both can be found using a spectrum analyzer, such as the one in the 'Luthier Lab' Android app. With that data you can calculate the Young's modulus along and across the grain, and the density. It might be hard to get the cross grain mode on a plank, but the long-grain stiffness is what's most important structurally. A heavy hammer might help, but if the boards aren't to big you should be able to pick up the sound with the mic on your 'phone or tablet. I can supply more details if you'd like.

[Dick Hutchings]

Where do you get boards like that?

[Alan Carruth]

They used to sell quartered spruce for staging planks.

[Eric Knapp]

Where do you get boards like that?

I am in Madison, WI, which is home to many boat and airplane makers. This place has been supplying those folks for a long time.

https://mccormicklumber.com/sitka-spruce

I was able to go through a large stack of boards, some much bigger than the one I picked. I liked the grain more on mine.

-Eric

[Dick Hutchings]

I think having the ability to look through the stack of boards is probably an important step.

[Clay Schaeffer]

You might want to check the runout on the boards before you mill them for guitar tops.