unscientific strip tests

matthew · Post by **matthew** » Thu Apr 03, 2008 11:28 pm

I cut six strips of wood I have in my workshop, keeping the grain orientation similar with each.

Each strip is exactly 10" long, 1" wide and 5mm thick (yeah I'm mixing up the standards a bit)

I have strips of WRCedar, Spruce (DB bracewood, no idea what variety), Celerytop, Silky Oak, Tas Oak and Crapiata. And one other strip of celerytop, cut crossgrain.

I soaked the strips overnight in water.

The strip that has expanded the most was the celerytop crossgrain strip, as you'd expect. It grew by about 6mm!

The other strips hardly changed longways. Interestingly, the strip that changed the MOST was the spruce! It grew about 1mm. The others barely noticeably, the silky oak about 0.5mm.

The only thing I can infer from this that the spruce strip is the most reactive to moisture of the woods tested.

I dried the strips out in the sun for two days and they all returned to 10" long.

I flexed the strips, unscientifically, and tried to grade them bendiest to stiffest. I got

Silky Oak
Tas Oak
WRCedar
Crapiata
Spruce
Celerytop

I flexed and tapped them all without looking. Most I could identify fairly easily. The two "oaks" are bendy but slower to spring back. The cedar is noticeably lighter but just as springy. The crapiata feels like the spruce, but a bit more flexible.

However I consistently mixed up the celerytop and the spruce. Every other time I thought I had a positive ID, turns out I was wrong. They feel very similar in spring and weight. The celerytop appears to have a lower tap tone than the spruce. This is the only way I can tell them apart by feel.

I was considering trying celerytop for back and sides but maybe I'd be better of trying it on a top?

I don't know if all this is interesting or just a waste of time.

Maybe someone could devise a series of useful more scientific tests and then twist the arm of someone with a good range of wood samples to test and share the results.

ap404 · Post by **ap404** » Fri Apr 04, 2008 12:08 am

I don't know if all this is interesting or just a waste of time.

It's interesting so far, and it's 100% empirically gained knowledge that you will always have on 'hand'.

Is it scientific ?

'Feel' is a science, otherwise how the hell would anyone figure out how to play a double bass and interact with the science of music ?

The 'invisible jukebox' blind testing sounds like fun too & you're storing away more information in your hands for your next table carve.

Cheers, A.P.

jeffhigh · Post by **jeffhigh** » Fri Apr 04, 2008 6:25 am

Surprised at the results for silky oak and tassie oak
The published results for MOE (modulus of elasticity) are higher than the other species you have tried.
But then timber is a variable item, you may have some low density samples.

matthew · Post by **matthew** » Fri Apr 04, 2008 7:12 am

what does the MOE measure exactly? Springiness or bendiness?

jeffhigh · Post by **jeffhigh** » Fri Apr 04, 2008 8:26 am

MOE is stiffness Higher is better
Ratio of Force required to produce a deflection
A good table here
http://www.worldwideflood.com/ark/wood/timber_list.htm
Jeff

Dave White · Post by **Dave White** » Fri Apr 04, 2008 8:44 pm

Matthew,

I had my shades ready based on the title of this thread but not a naked body in sight

You might find this OLF thread an interesting read with different set ups for deflection teasting discussed. Calculating Youngs modulus gives a measure of strength to weight which is an important measure.

jeffhigh · Post by **jeffhigh** » Sat Apr 05, 2008 11:54 am

Dave White said "Calculating Youngs modulus gives a measure of strength to weight which is an important measure"

I'm going to be a little pedantic here Dave, ex structural engineer here,
Youngs modulus has NOTHING to do with either strength or weight.
Think of it this way, laymans terms.

Strength is how much force it takes to break or permanantly deform a material

Youngs modulus measures Stiffness or how much a Force deflects or compresses or stretches a material.
So whilst rubber or wood might carry the same load, the rubber will probable move more and hence have a lower youngs modulus.

Once you have a MOE you also have to look at the density of the material to determine if the stiffness to density ratio is acceptable.

Dave White · Post by **Dave White** » Sat Apr 05, 2008 8:05 pm

Jeff,

Good point - but which Young's modulus are you referring to? I was meaning the one developed in 1884 by Zaccharia Young - who at the time was the worlds strongest, but not heaviest dwarf who wanted to demonstrate that weight wasn't everything and came up with his modulus to show this.

I say this as an ex-comedian

jeffhigh · Post by **jeffhigh** » Sat Apr 05, 2008 9:22 pm

AHH... ok Dave, I was only referring to the engineering Youngs Modulus not the Dwarf strongman Youngs modulus.

We had the difference between strength and stiffness drummed ito us at University...........a loooong time ago.
Jeff

Dave White · Post by **Dave White** » Sat Apr 05, 2008 10:49 pm

jeffhigh wrote: We had the difference between strength and stiffness drummed ito us at University...........a loooong time ago.
Jeff

According to the viagra SPAM e-mails I keep getting they are the same

I wonder who is going to be the first builder to finish their guitar tops with viagra

jeffhigh · Post by **jeffhigh** » Sun Apr 06, 2008 6:41 am

but Dave why bother, you already got wood

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