Official Luthiers Forum!

One of my current builds is for a friend. By the time I got all the imperfections out of this redwood I was at .095-.10 in thickness. That seems really thin for an OM even if I brace it heavily, right? Could it be safely put to use on a future parlor sized guitar? I hate to discard it because it's such a nice piece but will do so if that's the right thing.


Sent from my iPhone using Tapatalk

I wish is could flex it. Redwood can be just as stiff as spruce. The redwood top on my current guitar is .085. If you don't sand it until it's time to prep for finish, my hunch is that it's OK.


Sent from my iPhone using Tapatalk

I think it depends on how stiff it still is along the grain. How does its stiffness compare to the stiffness of other tops you've made that you were happy with?

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Maybe a 00?

I'd use it -- provided its not floppy length-wise, most of the redwood I've worked is very stiff in both directions.

_________________
Ken Cierp

http://www.kennethmichaelguitars.com/

Certainly can be made to survive with proper bracing. The only question is whether you'll like how it sounds.

As others have said, there's no way to know the stiffness just from the thickness. Especially with redwood. And you can't really do deflection testing when it's guitar shaped. So flex it with your hands and make your choice.

There's some redwood that's like cedar. Some redwood like spruce.
Which is it?

Next - just making a normal bracing scheme beefier to compensate for a thin top doesn't usually work out like you would think. The whole thing is a system.

Think of it like your floor. If you use 2x12 oak planks for your floor - you can use huge oak beams about every 4 feet apart for floor joists. If you use 1/2" plywood - you better have joists every 12". If you consider this to be a soft, floppy top - consider a double X or some sort of lattice bracing.

All that said - the current thickness is not outside the realm of "acceptable"... But the result is probably going to be a warmer sounding guitar.

Is there a rosette face down in that photo?

_________________
George :-)

Have you any idea about the density? Usually with softwoods the Young's modulus along the grain is proportional to the density. Some redwood, such as the 'LS' stick, is right up there in density and stiffness with Sitka and Red spruce. I can't thinl of when I've seen redwood that had density as low as most WRC.

You should be able to test offcuts from that top, as well. It's not as good as testing the whole top, but better than nothing. Make rectangular strips and suspend them like xylophone bars from rubber bands or threads .21 of the length in from the ends of the strips. Tap in the middle, and record the sound. From there you can use various methods to find the pitch. With that, and the dimensions and mass of the strip you can calculate the Young's modulus, and use THAT to find the 'correct' thickness. The hardest part with those small strips is getting accurate thickness and mass readings.

Use it.
Just make your X braces (if that's what you using ) thin(6mm)wide & 14mm tall at the the joint.
Taper them to the sides-NO thick brace at the side to top joint.

Flex the top & determine the direction you want to go in from there.

mike

_________________
Mike Collins

Thanks for all the responses! I'd try what Alan said but I already cut the scraps for soundhole reinforcement. I'm pretty sure I'll go ahead and build with it. I'm building it for a good friend. If it turns out to be a stinker, I'll build him another next year.



Mike, I'm not sure I'm following you. Are you saying that I should used tapered instead of scalloped X braces? I typically don't inlet the long legs of the x-braces to the sides. Should I consider doing inletting them for added stiffness/structural integrity?

Yes taper the braces to the sides.
From a high @the center joint to
2mm height to be inlet to the linings.
This 2mm height should be started at least 30mm from the linings.

This will help keep the center of the top strong & stiff but the edges flexible.
Sound & tone will be alive & well balanced .

And as already said reinforce the rosette area on the inside of the top.

Mike

_________________
Mike Collins

Thanks Mike! If nothing else this will be a learning experience. I'm building two other OMs in parallel - one red spruce and one Sitka.


Sent from my iPhone using Tapatalk