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Hello All,

I purchased some WRC Cedar locally and sliced it up this past weekend. I also ran it through my thickness sander and at ~.155 it feels flexible... This may be because I don't have very much experience (one parlor size guitar and a handful of tenor ukuleles) and come to you for advice.

They range from 18- 26 lines per inch and flex about 3/32" over a 6" span, under what I feel as moderate pressure (right before it feels like I will be stressing it too much and pushing my luck). I will be using these on a pair of Weisenborn style guitars with over size bridge plates. What thickness would you build a Cedar top Weiss? .125"? More than .125"? And how thick would you make the maple bridge plate?

Team

Left

Right


I hope to use be able to use them...

Thanks in advance.

_Mike

_________________
_Mike Tracz
MCT Guitars
https://www.instagram.com/mustcreatethings/
https://www.youtube.com/mustcreatethings

Mike-
Good question!
It sounds like you have digital calipers. If you can get your hands on a cheap dial gauge, you could get some numbers on the deflection of your wood- both lengthwise and across the grain.

Basically you just need to support the wood near the ends or edges and find the deflection with a known weight, over a measured span. That number, combined with info on the thickness of the sample (.155" ?) will allow for some calculations of Modulus of Elasticity aka 'stiffness'. Density info on the sample is also helpful.

Then it would be easier to compare your wood with other samples.

If you are interested in this, search on 'deflection testing' here at OLF or other sites online.

Cheers
John

Maybe I missed it, but I didn't see you mention how quartersawn it is. It may feel floppy because it's not cut really quartered. Also possibly the run out is severe. As long as it's quartered well, and the run out isn't horrid I don't see why you couldn't use it.

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John Mayes
http://www.mayesluthier.com

All softwoods share much the same microscopic structure, so there's a surprisingly good correspondance between density and Young's modulus along the grain. Cross grain stiffness relates most closely to the angle of the annual rings. Density is pretty easy to measure, although, of course, the thinner the piece is the less precise your thickness measurment will be. It's also possible to find the density (well, actually, specific gravity) directly: float a piece end-up in water, and mark how far up the water line is. If the piece is rectangular, and the mark is, say, 35% of the way up from the bottom, the specific gravity is .35, and the density is 350 kg/cubic meter or about 29#/cubic foot. That's low, but not uncommon for cedar.

At that density, I'd expect it to have a Young's modulus along the grain of about 8000 MegaPascals (metric units). If I read the conversion table correctly, that's about 1,160,000 psi.

Since the relatinoship between density and Young's modulus is linear, knowing where the other end of the line is allows you to figure out any point in between. For softwoods Red spruce and sitka tend to hold down the other end, with densities around 500 kg/m^3 and young's modulus along the grain of about 16,000 MPa., or 2,320,000 psi.

Cedar usually has to be thicker than spruce, due to the lower density and Young's modulus. Since stiffness is the limiting factor, and stiffness goes as the cube of thickness, you'd need to make a cedar top from the low end of the density scale about 26% thicker than spruce from the high density end: 1.26^3= 2.00. In between stuff will be in between..

How are you going to use 5" wide pieces to make a Weissenborn top?

I would not use cedar for a Weissenborn at all. Denser wood give them their characteristic sound.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Thank you all for the replies.

I plan on gluing up and adding wings for the lower bout and for the upper bout if necessary. Essential a 4 piece top. It is pretty well quartered and I'll post some pictures to verify. If I compare to a spruce top I purchased it is actually more vertical.

So I'm still on the fence about using it and will look into getting some deflection numbers to compare. I may be over thinking these bits. Maybe I should just go for it.

Thanks again. I'll post the end grain tomorrow.

_Mike

_________________
_Mike Tracz
MCT Guitars
https://www.instagram.com/mustcreatethings/
https://www.youtube.com/mustcreatethings

Building an instrument is a lot of work.

I would recommend that you use the highest quality materials you can afford

Here is a photo of the end grain...


I also did a gut check deflection with two sticks 18" apart and a 5lb weight. I placed to sections next to each other (~12" wide) and put the weight on their loose seam. At .155" thick they deflected .1875". Knowing that I still need to go wider and have thickness to play with I think they will be usable if the target deflection is somewhere around .2"-.25".

I feel good about them now.

Thanks all!

Best,
_Mike

_________________
_Mike Tracz
MCT Guitars
https://www.instagram.com/mustcreatethings/
https://www.youtube.com/mustcreatethings

i would say yes!
perfectly quartered stuff there.
of the 3 that i've made (weiss-style),
the best sounding is a bearclaw spruce top, not tight grained, and almost quartered, maple b&s.
the mahog top/back/side one is more focused, but quieter,
the aaa spruce top/koa b&s is more metallic for now, but is breaking in.
i'm still fine tuning bracing/arcing/etc for now and want to get some default design.
if you have a cutoff of some spruce from a top, and cut one from the cedar,
you could try bending them and see how they compare, and use your judgement.
probably make a nice sounding git.
good luck, and if it's your first weiss,and yer building from plans, the x-brace needs to be taller and thinner, imo.
also, the back brace at the break in the back should be heavier,
because when you bend the back, it wants to dish down there.
p.s...i still don't know what i'm doing, but i use intuition...

Hello Alan,

Could you explain what you mean by the brace where the back breaks? And what size do you recommend for the x-braces? I don't have plans. Just kinda winging it from all the info I've gathered...

_Mike

_________________
_Mike Tracz
MCT Guitars
https://www.instagram.com/mustcreatethings/
https://www.youtube.com/mustcreatethings

"Hello Alan,

Could you explain what you mean by the brace where the back breaks? And what size do you recommend for the x-braces? "

I'm the only Alan I see in this thread, and I didn't say anything about either of those that I can see. I'm not a Weiss man, so I can't give you much direct advice.

We all think you are pretty Weiss, Alan.

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Waddy

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