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So, you know that guy who sneaks into your shop when you're not looking to "help out"?
Well he stoped by when I was at lunch and sanded a Dread top to .105". It was clearly marked to be sanded to .115". Not the end of the world as I have plenty of stock to make a new one. I'd like to use this top for something. What size SS guitar will this work for?

Steve

It will probably be just fine for the guitar you were planning to make.
My spruce tops typically range from 0.083 to 0.105 depending on the body size and the specific piece.
I do use deflection testing.
My personal feeling is that most guitars are overbuilt, so that thinner top would more than likely be just fine

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Andy Z.
http://www.lazydogguitars.com

I'll second that. I go by mm so you're right at 2.6mm. That's well within the range of what I would use for a dread assuming its a nice stiff top. It will probably be better than it would have at .115" assuming its a pretty good top. Go for it.

BTW, I have dread I built about 4 years ago with a sitka spruce top that was thinned to 2.5mm in the middle and 2.3 around the edges of the lower bout and its still doing great, sounding great and pumping out some good music and has been played and played and played and played. Still good saddle height, action, etc.

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If you're not confident in your assessment of the stiffness of the top for the dreadnought than set is aside for use on a smaller bodied guitar.

Thickness of the wood can often become a benchmark when it shouldn't be. What is important is the relationship between the stiffness of the wood and the thickness (this is different for every piece of wood though, some minor and some major in difference) at which it is most stiff.

What your really want is to keep the plate stiff enough AND to get it as thin as you can (without compromising the stiffness though). There is no magic number, no hokus pokus to conjure up the perfect thickness, it just takes a lot of testing/flexing of a lot of tops in order to train your brain to know what is stiff and what is flimsy.

I agree with Andy, most guitars are well over built and I agree that most tops are thicker than they need to be too. One thing though that gets one to the place of understanding the stiffness of the the top in relation to the thickness is to be able to flex 100's of tops in order to be able to feel that difference. There is a local tonewood vendor near me that sells mostly cedar and I've been able to to just that. It really is amazing once you've flexed a lot of tops that you can feel the difference in the stiffness, even in rough sawn pieces at 0.150"+.

Having said this if you don't have the resources available to you to learn the differences between stiff wood and flimsy wood picking a base number is a good idea.

Generally speaking, most spruce tops are fine at 0.110-0.120"+ and Cedar is fine at 0.120-0.130"+.

My guess is that your top might be just fine to use for you guitar, but if you're worried at all about it, pick another one and use that one for an OM or smaller guitar.

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We go to that and thinner on occasion. Not to often and in fact the Scrap guitar currently doing down to about that. I still went with .250 bracing, I just went taller even more than norm. I am sure and will admit I am not one of the math or science guys here to determine bracing dimensions to stregnth all of that cube rule stuff as to when highth doesn't matter anymore to thickness. But we have gone really really thin, but not enough to get brace transfer from top and did fine. Is the rosette in? You may have to be really careful there and not go to deep as to go through, but enough when inlay it and rest of final sanding not mess that up.

I did type in Dread didn't I. This will be for an OM (just finished the mold and bending form yesterday).
The only deflection testing I've accomplished is my last three tops, one Cedar and two Sitka. Amazingly the 2 spruce tops were the same stiffness. Perhaps since I cut them from the same board. And the Cedar had more deflection at the same thickness. I bet you're in awe of my scientific prowess.
My main concern is that my finishing schedule usually includes four sessions of cursing and one or two sessions of stripping and resanding of things. For this guitar I think I'll take up Joe (JRE) on his offer to show me how to actually apply a finish.
Thanks for the advice. Time to forge ahead.

Steve

Oh it's an OM then. In that case pack it up and send it to me and select another top to use.....

It should be fine for an OM. Depending on the top it could have been fine for a dread too.

Steve, It's really, really hard to answer questions like this. It should be equally hard for you to trust the answers. Not that those answering don't know their stuff, no one has the wood in their hands except you. I've also built dreads that thin, even a little thinner, but it really depends on the wood. Also as a few have pointed out, you can compensate with you bracing style.
A quick check, does the top feel extra light compared to others in your stash? If it does I'd probably use it on a smaller guitar. If not, I'd use it as is and work with my bracing. The stiffness of the top tracks the density pretty well. Heavier generally denotes stiffer. Please note the word generally.

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Jim Watts
http://jameswattsguitars.com

Thanks for the opinions guys. I know it's kind of a general question and would yield general answers. The rosette is already installed so that won't cause any problems. The .105 was fresh out of the thickness sander and I lost another .003" getting the 100 grit scrathes out.
As far as the stiffness of this top, it is about the same as the two I got from Uncle Bob from his two tops for $15 special. Perhaps someone has experience with those tops and can tell me if that is stiff or not.
I am trying to lighten my guitars up but without being able to get my hands on a bunch of them as Rod suggests, it's a tad difficult to know where I'm at.

I would think it would depend a lot on the strength of your X braces. You may well be safe going that thin if your X is adequately strong. If you have doubts you could beef up your X braces and maybe even beef up your bridge plate to get some stiffness back into the center.

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And in case the top and bracing are a little on the flop side, does it help to use light strings instead of heavy or medium?

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