Official Luthiers Forum!

Hi!

More and more, I see suppliers offering Douglas Fir as top wood.
My girlfriend is begining in guitar making and she's interested by the idea of using douglas fir for her first classical.
Did some of you experienced this wood? I checked and saw that it's as dense as sitka or adi. Can some of you confirm that or speak about the tone of it?

Thanks a lot!
Francis

By the way... It's a wonderful thing to have a girlfriend that is building ukes and guitars in your basement.

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Francis Richer, Montréal
Les Guitares F&M Guitars

Whilst someone will undoubtedly jump in and say the have used it, heard it or heard of it,
for a classical the high density is not what the vast majority look for.
For classicals you are generally using the lower density spruces such as engleman, or western red cedar.
The nylon strings do not have enough energy to drive a dense soundboard.

I'd agree. I consider most sitka too dense for classicals and doug fir is definitely denser than sitka. I've heard of some pretty good results using it for steel string instruments but for nylon i'd stick to euro, engelmann, wrc, or maybe some lutz.

That's what I was thiking, but I also have to question in head...
Maybe it's stupid, but anyways... What about using a denser top (sitka, adi, or fir), and bring them thinner? What's the difference between a light wood top, thicker, and a dense wood, thinner ?

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Francis Richer, Montréal
Les Guitares F&M Guitars

I'm guessing that it wouldn't be stiff enough if it was thinned such that it had comparable mass. If you thin it enough so that it has similar mass as an engelmann, etc. top and, in its thinner state, it remains equally as stiff as the engelmann top then I don't really know. But I doubt this would be the case.

Yes that' the way it works, the crossectional stiffness is proportional to the square of the thickness.
Whilst the Douglas fir does have a slightly greater modulus of elasticity, by the time you thinned to an equivalent mass it would be too floppy.

Yhea Logic.

Thanks to you guys! I'll probably go for WRC and keep the Doug Fir idea for a SS.

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Francis Richer, Montréal
Les Guitares F&M Guitars

I built one with a rather heavy Euro top (435Kg/m3) and more important, of rather low stiffness. It tapped nice however. I made it thin enough to fix the weight issue, used the finest stiffness to weight braces I had and left them a bit taller, used stiffer and wider lining, a light bridge, my guitar shape is already on the small end, also well domed, and it turned out just about as good a guitar as my others built from lighter and stiffer (at the same time) spruce.

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Build log

I have used doug fir on tenor and baritone uke tops. Like the others I would hesitate on a classical though. Currently building an Om steel string with a vy well aged 4 pce doug fir top. I have thinned it to abt 2.2mm. Bon chance, and yes I would wait to assemble that top till sept . The humidity in MTL is way too high for guitar building in july/aug, Unless you have a room that is sealed to 50 % humidity dans votre bsmt.

Stiffness is proportional to the cube of the thickness, and inversely proportional to the square of the length.
Here is a hypothetical:
Assume Doug fir is 10% stiffer, and 10% denser than the normal spruce top. If you make the Doug fir top the same weight as spruce, it is only 80% as stiff. If you make it the same stiffness, then it will weigh 6.6% more than the spruce top.
One thing to consider is that Doug fir is quite variable in its properties, depending on where it grew. The fine-grained variety grown in the mountains tends to be less dense and stiff than coastal Doug fir. This is primarily due to the thinner latewood, when figured as a percentage of the total width of the growth rings.

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John

Yes you are right John, I plead mental impairment due to man flu/