Official Luthiers Forum!

I was gifted a really old, super stiff redwood top by a retired luthier friend last year and thought I'd give it a try. I had low expectations as my mentor in Spain often speaks of his distaste for the material but this top has an incredible tap tone and is stiffer cross grain than nearly every spruce soundboard I've used. I was curious how others have handled the material when building classical guitars, I've left it a bit thicker than spruce like I would with cedar (2.1 under the bridge) but it's still incredibly stiff. I'm not sure if I feel comfortable going thinner and was curious of other's experiences. The material is beautiful with exceptionally tight grain, rich medullary rays, and a "buckskin" like figure so it should make for a lovely looking guitar

I don't have any classical experience yet, but I did an archtop with curly redwood. Very low cross grain stiffness, the curl must have cut down the with grain stiffness,. I thought it was flimsy, but it looked cool, and that was what I had. It worked great. It is thinner than the dimensions in the Benedetto book, and 16" instead of 17." But it is entirely acoustic. That was the plan, it had to be thinner. The arching is more like a cello than an archtop. Parallel braced. It did rise some when strung up, then has pretty much stayed there.

Wood is pretty variable. If you think it is stiff, it probably is. But too stiff? What would you rather adjust; the bracing or the plate stiffness? Is there a different sound quality between a stiff belly with lighter bracing, and a weaker back with stiffer bracing. A perfect match would be best, but what one is the lesser evil?

The inlay is beautiful.

_________________
Why be normal?

With all of the softwoods I've measured the stiffness along the grain at a given thickness tracks the density pretty closely, and all of them follow the same rule. One of the things that changes this is curly figure, as Ken points out. So if you can find the density you can work the redwood top to the same thickness as a spruce top with the same density, and be pretty confident. Of course, there is some variation, and there's no substitute for actually measuring.

All of the redwood I've tested has been on the denser side; more like Sitka or Red ('Adirondack') spruce than Engelmann, but, again, all woods vary.

One thing that most of the redwood samples share is a low damping factor. In that respect it's like WRC, and sometimes even better. That's what produces the long, musical tap tone. It pairs well with a back material, such as Walnut, that has higher damping.

I'll note that, as with WRC, redwood has low peel strength. It tends to split easily, and you have to be very careful gluing on the bridge: make sure to do a light scrape on the top and the bridge bottom just before applying the glue to raise the 'surface energy'. I like to make the bridge wider on cedar and redwood tops: deeper along the line of string pull. This reduces the maximum stress along the back edge of the glue joint. I like to use walnut bridges for these, as it allows for the bigger footprint without adding weight. Also, if you finish the top before gluing on the bridge be very careful not to cut into the wood as you scribe the finish, especially along the back edge of the bridge.

Hard to tell from the pic but the latewood seems to be a high percentage of the wood as a whole. A specific gravity measurement while still in rectangular format would be very helpful in determining final thickness. If the redwood measured .43 or higher I feel you'll have a hard time balancing thickness vs weight.

_________________
Stay with the happy people.
--Reynolds Large