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#1
04-14-2016, 09:24 AM
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guitar thicknesses
What would be the optimal thicknesses for an OM size guitar? I'm thinking .100 for the top, .090 for the back and .080 for the sides. Does this sound about right. It's been a good while since I built one of these. Thanks, Danny Gray
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#2
04-14-2016, 09:28 AM
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I think that sounds about right, but...what kind of top wood, what kind of sides and back? I know nothing, but it probably has to be balenced with the size of the bracing as well
__________________
disclaimer I don't know anything, everything I say is a guess, estimate, hearsay, or opinion. For your safety, don't assume anything I say is a fact. Research
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#3
04-14-2016, 09:50 AM
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I don't have much experience building acoustic guitars, but as a repairman, I'd say .080" for the sides would be maybe just slightly on the thin side. You'll be sanding and scraping, so you might want to leave a little more margin. I've seen sides as thin as .060 or less, but when they're that thin, they're much more likely to crack. If you end up with .080" after sanding, then you're probably in the safe zone, for rosewood or mahogany. FWIW I see more cracks in mahogany sides than rosewood, but of course there's a lot more mahogany guitars out there. Mahogany does seem a bit more prone to cracking though IMHO.
I've seen lots of cracked sides, so from a structural standpoint, thicker is obviously better. As far as sound goes, thinner is arguably better. I guess it's a matter of finding the right balance. It'll be interesting to see what the builders here have to say on the subject. Last edited by Hot Vibrato; 04-14-2016 at 10:52 AM.
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#4
04-14-2016, 09:58 AM
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#5
04-14-2016, 10:26 AM
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__________________
disclaimer I don't know anything, everything I say is a guess, estimate, hearsay, or opinion. For your safety, don't assume anything I say is a fact. Research
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#7
04-14-2016, 11:14 AM
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Those sound like the numbers I'm looking at for my build with rosewood and sitka. I'm trying to build as light as I dare. As to the sides, I would be inclined not to go thicker in search of strength, but rather to reinforce the inside during assembly with muslin and perhaps side braces.
I'm planning to do both on my build with a muslin tape underneath a light side brace with a triangular cross section. The muslin should extend from underneath the top kerfing to underneath the back kerfing because otherwise it will leave a small unprotected area where the force of a side impact will concentrate, just before the seam with the side binding, and that can be where a crack appears. It's the weak link, so to speak. So it's important that whatever reinforcement is used does not stop before encountering the kerfing - but tapers under it or in some way becomes one with it.
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Taylor 815C '59 Gibson LG2 Washburn J4 jazz box, ebony tailpiece Gold Tone open back banjo Anon. mountain dulcimer Creaky old Framus 5/1 50 About 1/2 of Guitar One completed; currently intimidating me on account of the neck geometry. Stacks of mahogany, spruce, maritime rosewood, western red cedar Expensive sawdust
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#8
04-14-2016, 11:25 AM
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I went .095 mahogany before bending with my sides, for an archtop. Harder to bend, but there is so much going on with thick laminated sides these days that I didn't want to go thinner. The idea seems to be very stable sides force the top and back to do all the vibrating, like the skins of a snare drum.
Brian
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Brian Evans Around 15 archtops, electrics, resonators, a lap steel, a uke, a mandolin, some I made, some I bought, some kinda showed up and wouldn't leave. Tatamagouche Nova Scotia.
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#10
04-14-2016, 03:50 PM
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I do not build to numbers, but I have measured quite a few of my results, especially the visual outliers. Tops range from low .080's (classical) to as much as .135" (Engelmann jumbo). Sides from .050 to .090, and backs from .058 to .085. That's all recent history, perhaps the last 20 years.
Perhaps I should add that I do not take abusive handling into too much account, instead I build to performance standards and include enough structure to survive the long haul as far as internal stresses are concerned. I do expect my customers to have a certain level of care and respect, and do not think of my guitars as particularly fragile in day to day use. If I had my druthers, no one would build to numbers more than once or twice, just to get their bearings. The magic is released when building to structure, and the differences of a thou or two can be extraordinary, and whether should be less or more cannot be calculated until you're standing at the precipice. If I could influence the building community in just one way it would be this issue, for this is the path to mastery. IMO, of course!
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#11
04-14-2016, 04:20 PM
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While Bruce is right as usual, after building off and on as a hobby basis since the 70's, I have not totally dropped the yoke of measuring. While I'm more in the structure mood then measuring........the calipers come into play most of the times. This is mainly for feedback and a strange sense of assurance. One thing that has become apparent is that one develops a reasonably good ability to gauge sizes by eye. Another apparent thing is that wood varies enough that basic working to a certain size (especially for tops and backs) is out the window. Especially if one wants to have consistent output from guitar to guitar. The only regret I have in terms of how I have progressed is that I did not log the measurement results and outputs of various guitars in a journal.
Tom
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A person who has never made a mistake has never made anything
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#12
04-14-2016, 04:50 PM
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__________________
disclaimer I don't know anything, everything I say is a guess, estimate, hearsay, or opinion. For your safety, don't assume anything I say is a fact. Research
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#13
04-14-2016, 04:53 PM
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__________________
Taylor 815C '59 Gibson LG2 Washburn J4 jazz box, ebony tailpiece Gold Tone open back banjo Anon. mountain dulcimer Creaky old Framus 5/1 50 About 1/2 of Guitar One completed; currently intimidating me on account of the neck geometry. Stacks of mahogany, spruce, maritime rosewood, western red cedar Expensive sawdust
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#14
04-14-2016, 08:46 PM
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Wood varies widely in it's properties, such as the Young's modulus along and across the grain, which is pretty much what determines the bending stiffness at a given thickness. You can look up average values for this stuff, but any given piece of wood can be as much as twenty percent higher or lower than that for the long grain modulus, and 'way more in the cross grain. Factories work to dimension because it's about all they can do; it would simply cost too much to actually measure every piece. Most good makers measure somehow, either by feeling or tapping, or with some more objective system such as deflection or vibration testing. However they do the measurement they let that determine the thickness. This is particularly important on the top.
Also: the 'correct' thickness for any given top will depend on the system the particular maker uses. Things like the brace layout and profiling, whether the top is tapered in thickness or uniform, the size and shape of the guitar, desired sound, the phase of the moon and the price of coffee; in short, all the usual variables come into play. Well, maybe not the moon, but coffee.... 
Last edited by Alan Carruth; 04-14-2016 at 08:54 PM.
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#15
04-14-2016, 09:23 PM
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