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Hi All,

I have a chance to get a decent price on some resawn Honduran Mahogany. Since I don't own a drum sander and don't want to hand plane this wood, I was planning to have the vendor thickness the wood for me and I want to make sure I get a safe (but tonally satisfying) final thickness. NOTE: I don't have any technical data on the wood (density, etc).

Since I'm a little unsure whether thicknessing to a number will get me the tonal results I'm looking for, I started researching thickness sanding guitar plates. I came across the following video on thicknessing a top by Chris Paulick and he mentions that he thicknesses the top until it starts to get a sheet metal like sound when you hold it between your hands and flex the wood. At the end of the video you can hear the "sheet metal" sound he's talking about: http://www.youtube.com/watch?v=xDDJVAaD9n8.

Also, in a recent thread, Mr. Brondel mentioned that for backs he removes material until the wood takes on a "musical" quality.

Given the above, here are my questions:
1) What would be a good safe, nominal (but hopefully tonally satisfying) thickness for Honduran Mahogany backs and sides for a Dreadnought build?
2) Is the "sheet metal" sound the kind of "musical" quality I'm listening for when thicknessing back material too? What about the sides?
2a) If I'm not listening for a "sheet metal" sound when thicknessing backs and sides, what kind of "musical" sound am I listening for?
3) Does anyone have a video on thicknessing a back/sides similar to the Chris Paulick video, where I can hear the change in the wood?

Thanks,

Erik

Well you may get the sides to a specific thickness. Anywhere from .070-.095ish, depending on who you ask and how they build. I would say .090 would be a safe bet to leave you a little sanding room as you go. The back is a different story, because the halves are usually joined at around .125ish and then thicknessed to final dimensions. To join wood thicknessed to final dimensions would be tricky. But, .090 is probably a good safe back thickness as well.

I'm in no position to answer your question, but I will say that the sides are typically thicknessed based on how easily the wood bends (not by a musical quality) and the shape of the body (tight waist, cutaway, etc.).

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Formerly known as Adaboy.......

Personally, I don't believe in the "sheet metal sound". The sheet metal sound is pretty much an indication of stiffness across the grain only. IMHO the more important aspect, especially for structual concerns is the stiffness along the grain. What I'm looking for when thicknessing a back is the taptone/pitch. As you thin the joined plates the pitch gets higher, due to the reduction of mass. When you get to the magic point the pitch will stop rising, and then start to drop. This is due to the reduction in stiffness.

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

Interesting, Woody.
I'll try anything in that department.

Mahogany sides: between .080" and .085" before bending. Run out and wild grain will make bending mahogany a miserable experience. Don't wet it too much and bend hot and fast.
For a dread back I wouldn't go under .095", and probably not over .115". It depends on the particular piece density and stiffness. Like Woody, I would be more concerned about longitudinal stiffness. Cross-grain stiffness is almost irrelevant, especially since the back is (traditionally) ladder braced.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

When you say "have the vendor thickness the wood" - I'd be extremely particular about what you are looking for here. All the measurements quoted above are for the back and sides once planed or sanded, so the surface is very smooth.

So if the vendor interprets the thickness at .110, for example, with saw marks remaining, you'll be sunk. On my bandsaw I need to leave lots of buffer when resawing to enable smoothing with the drum sander.

All the '70s D-18 Martins I measured were .115" for the back (and incidentally for the sitka top as well), which means they were probably thicknessed between .118" and .120" before finish prep. That's how I interpret it anyway.
The sides are all over the place since kinks and dips seemed to have been smoothed out with aggressive sanding (I imagine on a 6 x 48 belt sander, 70s craftsmanship at Martin is on average not the best). Thus the last D-18 I restored had sides .050" thick in places, original finish and miraculously, no cracks.

Getting the vendor to thickness the back to final thickness strikes me as a very bad idea. It wrongly assumes you'll be able to perfectly join the plates (without need of levelling between the two halves), and you have no idea of the density of the specific mahogany you'll get. Plain mahogany is not the worst wood to hand plane BTW, and maybe the easiest with Spanish cedar, and it sands very easily with an orbital sander to clean plane marks.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Double post.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I had that same situation not long ago. The supplier was a guitar guy and I asked him to do it according to the wood. It worked well at about .80 and .100. It wasn't honduran, though.
I hear that sheet metal sound all the way through Chris's video. That's a good technique, but I think you have to be there.

For me .080-.090 for the sides and ~.090 for the back.

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John Mayes
http://www.mayesluthier.com

Thanks for all the replies guys.

I think I've got this worked out. Just waiting for confirmation from the vendor.

I'll get everything delivered at about .140 thick rough sanded to remove saw marks. I'll have to join and thickness sand these myself. I may have to pay LMII to do it, unless I find someone local.

Anyone know someone who can do thickness sanding in the Northern California Bay Area?

I'd prefer to work on it myself (with someone experienced to guide me), so I can get some experience with the wood and how it changes as I bring it down to final thickness.....same for the tops I have coming (Carpathian Spruce).

Well, thanks again.

Erik