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Cedar Siding for a Top?

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Cedar Siding for a Top?

Postby Eric Knapp » Sat Apr 08, 2017 2:06 pm

Hello, I'm going through my wood stack looking for practice wood and potential instrument quality wood. I uncovered a piece of cedar siding I kept from a project on an old house. It is 12 feet long and 9 1/2" wide. It is perfectly quarter-sawn and very clear. One end had a crack for a bit so I cut a hunk off and planed it up to see what it looked like. It's quite nice. It is tapered on one edge so I couldn't book match, I'd have to use consecutive pieces.

I am planning on using this to make a practice top. Is it possible this might be usable in a guitar? Or maybe even a practice guitar that I would complete?

Thanks,

-Eric
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Re: Cedar Siding for a Top?

Postby Barry Daniels » Sat Apr 08, 2017 2:53 pm

Is it possible? Most likely. I used some cedar siding for a dulcimer once and it worked fine. How many grain lines per inch is it?
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Re: Cedar Siding for a Top?

Postby Eric Knapp » Sat Apr 08, 2017 3:50 pm

Barry Daniels wrote:Is it possible? Most likely. I used some cedar siding for a dulcimer once and it worked fine. How many grain lines per inch is it?

It looks like it's around 44 lines per inch?

cedartop1.jpg
Over 40 lines per inch?


I gave it a quick thin shellac wash to see the grain better.

cedartop2.jpg
A little shellac wash to show the grain.


How does it look? It cut beautifully on the bandsaw. I surfaced it with a smoothing plane and that was, well, smooth.

-Eric
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Re: Cedar Siding for a Top?

Postby Barry Daniels » Sat Apr 08, 2017 4:11 pm

Looks pretty decent to me. Does it have a tap tone?
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Re: Cedar Siding for a Top?

Postby Eric Knapp » Sat Apr 08, 2017 5:35 pm

Barry Daniels wrote:Looks pretty decent to me. Does it have a tap tone?

I'm not experienced enough to judge the quality of a tap tone. I thinned a small piece down to 0.1" and it rings with a nice sustaining tone when I tap it. I held it at various spots and all the tones were pleasant to my untrained ear. I suspect it takes a while to know what a good tone is.

Thanks,

-Eric
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Re: Cedar Siding for a Top?

Postby Clay Schaeffer » Sat Apr 08, 2017 5:44 pm

With tight straight grain like you have, flipping consecutive pieces can give you close to a book matched effect. Could make a very nice top.
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Re: Cedar Siding for a Top?

Postby Alan Carruth » Sat Apr 08, 2017 6:03 pm

Note that cedar often is less dense than most of the spruces. In softwoods the Young's modulus along the grain pretty well tracks density, so you may want to leave it a bit thicker than you would a spruce top to keep the stiffness up. Since the relationship between density and Young's modulus is linear, while the stiffness goes as the cube of thickness, making a low density piece of wood thick enough to get the stiffness up usually results in a lighter top than a thinner, denser piece.
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Re: Cedar Siding for a Top?

Postby Eric Knapp » Sat Apr 08, 2017 11:48 pm

Clay Schaeffer wrote:With tight straight grain like you have, flipping consecutive pieces can give you close to a book matched effect. Could make a very nice top.

Thanks, Clay. I was hoping that might be the case. I have just cut two hunks off and I'm going to try it. The wood works really easily.

-Eric
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Re: Cedar Siding for a Top?

Postby Eric Knapp » Sat Apr 08, 2017 11:54 pm

Alan Carruth wrote:Note that cedar often is less dense than most of the spruces. In softwoods the Young's modulus along the grain pretty well tracks density, so you may want to leave it a bit thicker than you would a spruce top to keep the stiffness up. Since the relationship between density and Young's modulus is linear, while the stiffness goes as the cube of thickness, making a low density piece of wood thick enough to get the stiffness up usually results in a lighter top than a thinner, denser piece.

Thank you, Alan. That is fascinating. Knowing the density of spruce and cedar, could I scale the thickness up from 0.1" for spruce to a good thickness for cedar?

-Eric
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Re: Cedar Siding for a Top?

Postby Jason Rodgers » Sun Apr 09, 2017 11:20 am

"Tonewood" is what you make it. Build something beautiful, and be sure the first thing you tell people after "Look at this guitar I built," is "... and the top came from a piece of siding."
-Ruining perfectly good wood, one day at a time.
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Re: Cedar Siding for a Top?

Postby Eric Knapp » Sun Apr 09, 2017 1:19 pm

Jason Rodgers wrote:"Tonewood" is what you make it. Build something beautiful, and be sure the first thing you tell people after "Look at this guitar I built," is "... and the top came from a piece of siding."

Ha! Cool, I will say that. Now I have to decide what to build with it and what wood to use for rims and back.

-Eric
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Re: Cedar Siding for a Top?

Postby Randolph Rhett » Sun Apr 09, 2017 1:39 pm

Some of my nicest guitars have come from urban trees or reclaimed lumber. I made an archtop from redwood reclaimed from a water tower. The wood had to have come from a thousand year old tree felled in the 19th century. (I did not do it justice, to my deep regret.)

"Tonewood" is a marketing label. It is a great and valuable service that there are lumber yards milling rough lumber into 1/8" blanks for luthiers. If I could actually connect with a reliable customer base it would make good economic sense to use their services. But they are milling Spruce and Cedar, not "Tonewood".
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Re: Cedar Siding for a Top?

Postby Peter Wilcox » Sun Apr 09, 2017 2:02 pm

The first guitar I made was from cabinet shop cutoffs, field fencing and a copy machine. Another one from a toilet seat, plastic kitchenware, drywall screws, formica, piano tuning pins, and HO tracks. Cedar siding is an exponentially better material. :D
Maybe I can't fix it, but I can fix it so no one can fix it
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Re: Cedar Siding for a Top?

Postby Aaron Helt » Sun Apr 09, 2017 2:33 pm

Was that mother of toilet seat or just plain seat?
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Re: Cedar Siding for a Top?

Postby Alan Carruth » Sun Apr 09, 2017 6:37 pm

To really know the best thickness you would want to get some test data on the stiffness of the piece in hand. Wood is a natural material, and varies. In general, the stiffness of softwoods tracks the density pretty well; about 60% of the samples I test are within 10% plus or minus of the Young's modulus you'd predict on the basis of the density. Some, however, are 'way out. Wood with a lot of run out will have low long grain stiffness, 'reaction wood' or 'compression grain' will be denser than it 'should' be for the measured stiffness, and you can see those things. Still, there are some pieces that are less stiff than you expect, or stiffer. On the whole, though, if there's no run out to speak of and the latewood lines are not really heavy it's probably within the range.

If that's the case (and I can't guarantee it!) you could find the likely Young's modulus graphically. Determine the specific gravity of the piece; it's density in relation to water. Most of the wood we deal with for tops falls between .30 and .50 in SpG: between 18.75 and 31.25 pounds per cubic foot (or 300 to 500 kg/m^3). At the low end you'd expect a Young's modulus of about 6000 megaPascals (metric measurement), and the high end would tend to be around 16,000. Graph out that straight line, find the point on it that corresponds to the density, and go over to the Young's modulus side to find that. I use a simple 'index number' system to find the correct thickness for the top from there.

The 'correct' thickness is predicated on the notion that you need to make the top stiff enough to resist long term static bridge torque, and that's mostly a function of the stiffness of the top along the grain (and the bracing, of course), as well as the string tension and string height off the top. Since the top stiffness is a function of the Young's modulus and the cube of the thickness, when you know two of them you can find the other. In this case, what I've done is to multiply the Young's modulus times the cube of the thickness (in millimeters) of some tops that I've made that worked to get an 'index number'. On my guitars I find that it's around 250,000 for steel strings, and 150,000 for Classicals. Again, this is a number that works for me, given the way I work: it might not work as well for you. Still, it's a place to start.

So, suppose your cedar has a SpG of .35. That implies that the lengthwise Young's modulus is around 8300 mPa. Dividing 250,000 by 8300 gives 30.12. The cube rot of that, which is the suggested top thickness in mm, is (drum roll) 3.11, or about .125". Given the way the numbers usually work out, that's got a better than even chance of being pretty close to the 'correct' thickness, and only about a 20% chance of being too thin (and probably not by too much if it is), assuming you use a brace pattern that's similar to mine and so on.

I hope that makes some sense. Gore gives a much more complete treatment of this in his books: my method is pretty simplified, but has worked fairly well for me and my students.
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Re: Cedar Siding for a Top?

Postby Randolph Rhett » Mon Apr 10, 2017 2:12 am

Alan's way is definitely the simplest and easiest to understand. A far more complex way that some luthiers have used is to mill it a little thick, join it, and flex it long and cross with your hands. Compare it to other tops you've done. If it feels a little stiff, maybe thin it a little. But don't let me over complicate it for you.

;-)
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Re: Cedar Siding for a Top?

Postby Eric Knapp » Mon Apr 10, 2017 8:51 am

Randolph Rhett wrote:Alan's way is definitely the simplest and easiest to understand. A far more complex way that some luthiers have used is to mill it a little thick, join it, and flex it long and cross with your hands. Compare it to other tops you've done. If it feels a little stiff, maybe thin it a little. But don't let me over complicate it for you.

;-)

Ha! Well, a bit of a confession. I'm a faculty member at a college where I teach computer programming. I like the way Alan talks and can even understand it mostly. What I don't understand today I'll understand tomorrow as it will make me curious. A curious geek is a fast learner. :arrow: :geek:

And thank you for your simplified approach. I have to start somewhere and since I haven't made any tops yet I have no way to compare them. This is my start and I'll have to go with a measurement this time. I'll flex it to get the feel of it for future comparisons. I think that's one of the advantages of doing an apprenticeship with an experienced maker. There are samples laying around to try. I'm old and doing this on my own. If I make a great or even pretty good guitar someday it will be an accident.

-Eric
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Re: Cedar Siding for a Top?

Postby Eric Knapp » Mon Apr 10, 2017 9:03 am

Alan Carruth wrote:So, suppose your cedar has a SpG of .35. That implies that the lengthwise Young's modulus is around 8300 mPa. Dividing 250,000 by 8300 gives 30.12. The cube rot of that, which is the suggested top thickness in mm, is (drum roll) 3.11, or about .125". Given the way the numbers usually work out, that's got a better than even chance of being pretty close to the 'correct' thickness, and only about a 20% chance of being too thin (and probably not by too much if it is), assuming you use a brace pattern that's similar to mine and so on.

I hope that makes some sense. Gore gives a much more complete treatment of this in his books: my method is pretty simplified, but has worked fairly well for me and my students.

This does make perfect sense to me. Based on general data I had estimated my wood to have a SpG of 0.35 and was close to the 3.11mm thickness. I was going to start with 3.5 or 3.4 as I don't know how much is taken off with final surface preparations. Gore's book is not in the budget at this point. I need other tools and supplies first. I do want it someday.

Thanks for the detailed reply, Alan. I always read your answers carefully and have learned a ton. In a different life I would have been one of your students. Now I learn from a distance and I'm grateful for the internet and its reach.

-Eric
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Re: Cedar Siding for a Top?

Postby Alan Carruth » Mon Apr 10, 2017 2:32 pm

Several years ago one of the folks in Karl Roy's violin making summer class tested him out to see just how accurate he could be in flexing samples of wood. The student made up a shoe box full of wood slips of different stiffness, and had Karl sort them out in order several times during the week. He found that Karl could reliably feel a difference of only 3%, which is probably close to the experimental error in the measurements I do. OTOH, subsequent similar trials at a violin maker's meeting disclosed that most folks are not nearly as good at it as they think they are.... ;) I agree that my method is more complex than just tapping and feeling, but it's pretty reliable, and I can teach it to a beginner on line. Roy had about 60 years experience behind him, and that method is notoriously hard to teach. Using both methods is better than either alone, of course.
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Re: Cedar Siding for a Top?

Postby Brian Evans » Tue Apr 11, 2017 8:42 am

FWIW I made a quite nice archtop top from cedar deck planking that I got at Home Depot. WRT to the idea of comparative stiffness testing, I think it's fair to say that testing a number of coupons by feel, all at the same time and one after the other, has a far greater likelihood of success than testing the same coupons say two weeks apart, one at a time. As part of my next build project (I always try to do builds that have new things in them, that haven't been widely tried to my knowledge, or that are new to me) I am going to build a deflection tester to track the stiffness of an arch top as I carve it. I figure a bridge, a dial indicator, a digital scale and apply incremental downward load with my bridgeport quill should work and be extremely repeatable. It will be interesting to say the least. What it will guide me towards I have no idea. Anyone know what the ideal archtop top deflection under a typical string down-load of 35 lbs is? :)
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