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a couple of questions????

I have two AAA sitka tops I am building and thought I would try to try to get some consistency ...

the first one is thicknessed to .115 , the board is spaced on two rails 18 inches apart lengthwise and with 5lbs , two pcv tubes filled with pennies and taped together it deflects .160...I have Kent Everett's video on voicing a steel string guitar, the board has a very loud warble and seems to be fairly stiff...
I remember watching Chris Paulicks video and he suggests thinning until the deflection is .250??
should I go thinner staying above .105 to get to .250 deflection????
also this is before installing rosettes..

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MK5acoustics.com

the second board is thicknessed to .120 has no warble and deflects to .170

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MK5acoustics.com

Everyone is entitled to their opinion, which also means they're entitled to dis agree with mine.

Personally I think the "warble" sound is BS. If I'm understanding it correctly it would only be an indication of stiffness across the grain. Stiffness along the grain (end to end) is more important for the structual stability (and tone IME) of a guitar than stiffness across the grain.

I don't believe there's a magic formula. Use whatever method you're comfortable, and learn from your results.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

its along the grain

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MK5acoustics.com

Wes: For what it's worth.....I do deflections similar to you. I aim for a deflection in .200-.210 range and don't worry much about thickness. I think the good thing about deflection testing is that you can develop consistency in your top stiffness. This gives you a baseline from which to work that flexing by hand does not allow especially in my case dues to low output of guitars. Even someone making 12 guitars a year does not get much experience flexing and thining tops.I tend to agree with Woody in regard to the warble sound,it happens but as you have seen, to varying degrees and is something you have to gage by it's feel and sound compared to a dial indicator for deflection testing. Good luck in your search for the correct info. I think a lot of it is good, you just have to figure out what works for you. Lots more coming I'm sure.Take care.
Tom

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A person who has never made a mistake has never made anything!!!

I think Woody is referring to warble as being an indication of cross grain stiffness.

From your numbers, and reading around quite a bit on my own, I would say you could go a bit thinner. .200 seems to pop up quite a bit as a good point of reference. But of course it all depends how you brace it etc. etc. as the variables pile up. I note that your first board is much stiffer than the second. The only way to find out for sure is to build one and see what your impressions are, adjust, build again etc.
In my opinion, based on how I build, which I would expect to be about average, .250 is a bit too thin. I used the same Paulick vid as a reference and built with a top at .92" (.250 deflection, 5lb @ 18") and I don't really like the guitar. I speculate that .250 came secondhand through Somogyi students. But Somogyi says he uses 3/4" tall bracing, which is a good bit taller than most folk round here I'd say.
But again, I speculate.
I would say though that it is better to have your top a bit too thick than too thin.

I'm getting ready to do my first deflection measurements tomorrow. Thanks for bringing this up. It will at least help me to get in the ballpark.

Can someone confirm for me when you're throwing around these numbers that you're talking about a joined plate, not half a top?

Mike

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Mike Lindstrom

Joined plate.
I do mine with rosette in but soundhole not cut out.

Is there a tutorial out there on this deflection thing ??
I've been doing the warble test at around .110-.120
I'd love to see some pics and specs.
Gregg

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Gregg

The warble sound?

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Rian Gitar og Mandolin

Arnt: Kent Everett has a DVD on" Voicing The Steel String Guitar" in which he describes how he determines when his tops are thinned to his desired thickness. Similar to holding a piece of sheet metal between your both hands and shaking it to make a warble sound.Not my cup of tea but seems to work for him.
Tom

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A person who has never made a mistake has never made anything!!!

Robbie Obrien has a video as well. Interesting though is the second set which deflects a little more but is a little thicker has almost no warble.. FYI sets came from different places , maybe someone can chime in on cross grain thoughts.

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MK5acoustics.com

Wes - based on my very limited experience I think the weight of the top would come into play too. For instance....it would be great to have a top that only deflects to .200 and is .100 thick....but what if it weighs a lot more than a top with comparable deflection data? In my view the top with the lower weight would be the go to top in this scenario.

A very good learning exercise would be to dimension every single top in your inventory to the same dimensions (length, width, and thickness). Deflection test and weigh every single one and compare that data. For me that would be a couple days worth of work but it is my suspicion that I would learn quite a bit. Not just about the variance that we know exists in wood, but about the way the tops feel and sound in your hands. I know for a fact that I have tops in my inventory that feel better than others but I have no idea how that translates to usable numerical data....hence the two days worth of work.

One last thing...I've paid for and watched the Everett DVD's and while I think some good information can be learned from them, like Somogyi, I don't think he gives you magic answers. If I were Somogyi, Everett, Ryan, etc....I would be careful to protect certain secrets I've discovered if I had paid for it with so many years of trial and error.

Chris

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There is no difference between the man that thinks he can....and the man that thinks he cannot.

Robbie Obrien has a video as well. Interesting though is the second set which deflects a little more but is a little thicker has almost no warble.. FYI sets came from different places , maybe someone can chime in on cross grain thoughts.

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MK5acoustics.com

Oops double post from my Iphone

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MK5acoustics.com

An 'ideal' deflection probably depends on a lot of things... the body size, the bracing pattern and heights, the tone you're looking for, etc. I've not tested it, but I think it also depends on how 'interlocked' the bracing pattern is. E.g., do braces butt-up to each other so the end of one is glued to the side of another, or are they tapered to zero at the end? For my student's simplified dread and GA bodies (with no interlocking braces except the X), I found 0.18" deflection (5 lb @ 18") gave a bass-balanced sound that lacked treble. 0.14" deflection gave a better balanced sound (for our Sitka tops, that corresponded to an _average_ thickness of 0.110").

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David Malicky

I've done deflection from .200" to .470". When you get below .200" I think you need to change your bracing scheme to provide more support. At .470 the top has a tap tone similar to limp cardboard. It does come alive once strung up.
Balance of bass and treble for my builds are more about bracing and voicing than top thickness. An over-braced thin top will not have much bass response. A thicker top that is braced to move well can have pretty nice bass.

I've done thickness down to .075". Try it if you are man enough.

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

I use 5 lb 4.4 oz. Yes, those numbers came from a students top. Use it as you will.

The thing is, no matter what numbers you get from where, you still have to go through the building process entirely and then judge whether or not you like the results. Then, whatever numbers you use, you will have a reference to go by. As well as determine whether the tops elasticity alone is what makes you like/dislike that guitar. So, even deflection data is only a starting point.

True, no arguement here.