#16
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That's what I'm saying. Thin a Sitka top to .110, measure the deflection with your rig, build a dread (likely the most referenced acoustic guitar sound), bam, you have your first reference point. Adjudicate and adjust.
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#17
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Okie dokie.
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Solo acoustic guitar videos: This Boy is Damaged - Little Watercolor Pictures of Locomotives - Ragamuffin |
#18
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#19
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For the first hundred guitars or so, we would deflect each brace with a given weight and record the number. Then we would cut the height down to 11/16" and re-deflect. We would use the two numbers to see if the braces were becoming floppier with material removed. Short answer is yes some braces do occasionally become much less stiff the thinner they get, but most of our bracing stock generally loosens proportionally to height. So now we only do one deflection test on braces. |
#20
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Rog,
I am no expert but have seen that a good deflection starting point on just the top without braces is, top blocked at 18" apart and a 5 pound 5 oz. weight in the middle you want 1/4" of top deflection. The video I saw was with the top pieces joined but the shape of the guitar not cut out. When doing this a lot of the Sitka tops I have checked start to end up around .110" - .115" give or take with 1/4" of deflection. So set up two 3/4" tick boards 18" apart and get one 1/2" thick and put it in the middle. Keep taking a little off the top and keep checking until it touches the center board with the weight in the middle of the top. Of coarse you can make a much more elaborate set up with a dial indicator but you can get it done this way. That is at least a starting point. If you do it this way at least you have some sort of consistency. |
#21
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It's funny because I went through the same thing that frog did a couple years ago and was frustrated but this (Halcyon says below) is exactly what you have to do.
I don't even know what the brick I use weighs actually, I jsut know that it is the brick that I will use till the day I build my last guitar. Quote:
Last edited by redir; 05-04-2017 at 06:57 PM. |
#22
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#23
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Solo acoustic guitar videos: This Boy is Damaged - Little Watercolor Pictures of Locomotives - Ragamuffin |
#24
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One advantage of getting numbers on things like the mass of the brick and the spacing of the supports is that you can convert your idiosyncratic deflection numbers into standard units, such as Young's modulus. Then you can trade information with other folks who have done the same, even if they use different methods to find the numbers.
Another advantage is that you don't actually have to keep checking until you get the 'correct' thickness; you can crank the numbers into formulae (which can be pretty simple) and find the proper thickness after one measurement. There are several sources that can tell you how to do this. One is David Hurd's book and the Gore/Gilet books are another. If you want to dig around a bit there are older articles in places like the 'Journal' of the Catgut Acoustical Society and the old 'Journal of Guitar Acoustics' that get into this as well. Material testing is a pretty standard discipline in mechanical engineering, and there's lots of information out there. |
#25
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Solo acoustic guitar videos: This Boy is Damaged - Little Watercolor Pictures of Locomotives - Ragamuffin |
#26
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Thanks everyone for the info!
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Solo acoustic guitar videos: This Boy is Damaged - Little Watercolor Pictures of Locomotives - Ragamuffin Last edited by rogthefrog; 05-06-2017 at 05:12 PM. |
#27
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#28
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The deflection is a hair under 0.315, so about 5/16.
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Solo acoustic guitar videos: This Boy is Damaged - Little Watercolor Pictures of Locomotives - Ragamuffin |
#29
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Well there you go. Now write that down and begin the very slow process of changing things up and recording everything you do and the changes they make. Then in 10 or 15 years you should have a pretty good idea what works best.
Pretty simple huh? This is all in good fun... Have fun with your build. |
#30
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Solo acoustic guitar videos: This Boy is Damaged - Little Watercolor Pictures of Locomotives - Ragamuffin |