Official Luthiers Forum!

I'm planning on making a 'lap friendly' and short scale derivation of a Martin Herringbone dreadnaught. I purchased a set of drawings from StewMac a while ago and just made a copy at 93% of the original size. Dimensions closely emulate those of a Martin Dreadnaught Jr.

What I don't know, is how to size the tonewoods. For example, the drawing says the back is .100". Nice round number. If I reduce it to 93% of its original size, I get another nice round number, .093", or 3/32" for those using fractional dimensions. But....the area of the pieces, and the volume of the box change much more than 7%.

I'd like some suggestions as to appropriate wood thicknesses of back/top for the guitar made from the shrunken drawings.

Thanks very much.

_________________
Peter Havriluk

Most plans have pretty hefty dimensions for back, sides, top, and braces, and if you build to these values you will likely be way over building. The plans don't take into account what materials you plan to use or what sound you are hoping to achieve. I'll leave it to those who know better than I, to advise you, based on your wood selection. Don't trust the plan diagrams to be to to scale. Good luck with your project, Peter!

Alex

_________________
"Indecision is the key to flexibility" .... Bumper sticker

Alex, thanks. I made no mention of side thickness, as those components answer to their own unique needs. I'm hoping for an overall perspective of how do we choose thicknesses for tops and backs of varying sizes. We'll see how the responses work out.

_________________
Peter Havriluk

Peter: Alex is right about most plans that are out there, some more so then others, but I think the Stew-Mac dread plans are quite well done and if one follows them the result should be a nice guitar. My experience with reducing size is that the bracing sizes are not proportional, most likely due to the cube root rule, but at 7% reduction I would not think much more would be required. After all that, carry on in the way you are going, I think you will be OK.
Tom

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

Thanks, folks. We're making some progress. I was thinking a bit, that the top of my shrunken dreadnaught is more-or-less the size of a '00' guitar. Anybody know what the general rules are for top thicknesses of various body sizes of guitars? I'd think a Jumbo would have a thicker top than a 00, for example, and that a cedar top wants to be thicker than a spruce top. But how much to initially plan for?

_________________
Peter Havriluk

A 7/8 scale dreadnought would be just a bit larger than a Martin grand concert (00) or the Gibson L-00. The same brace sizes used for those smaller guitars could work for a scaled dreadnought of the same general top width and length, yes? It seems to me that the scaling work for the bracing has already been done and tested on hundreds of thousands of guitars if that is the case.

_________________
A constellation only takes shape when one maps the whole.
- Beth Brower

For a 00 size, I would make the top around 0.105". Of course, stiffness of the individual top and the desired tone are variables.
The X-bracing should be around 1/4" wide and 1/2" tall.
The first several dreads I made were a 96% scale (15" lower bout), and had a 24 3/4" scale length.

_________________
John

John, thanks for the advice and comments. I'd guessed that I could use 1/4" wide bracing, didn't know a starting height. Now I have some parameters. Much obliged.

_________________
Peter Havriluk