Wood Stiffness and Hardness

[JCKelly]

Well, this is mostly incomprehensible engineering stuff, but you might want to look over:

http://nanovea.com/wp-content/themes/wp-nanovea/Application%20Notes/wood-hardness.pdf?utm_source=streamsend&utm_medium=email&utm_content=25414195&utm_campaign=High%20Temp%20Morphology,%20Nanoindentation%20&%20Scratch%20Hardness

The upshot of it you probably already know (I never thought of it).
Regarding the three woods, maple, walnut and cherry -
Walnut is the stiffest and hardest, followed by Cherry with Maple clearly in last place.

The metric units of stiffness I'll not convert, but they are good for comparison.
Walnut ~2.25 GPa    Cherry 1.7 and Maple 0.8

This means that if you used a wooden board as a springy thing, and hung a weight on it: However much a walnut board would sag,  a Maple board would sag nearly three times as much (2.8 times)

Maybe that's why the Army, who weren't so concerned about pretty grain, used walnut whilst JP Beck chose maple.

So, is it a sin to look at mechanical properties of wood much as this P.I.T.A. metallurgist would steel?

Heh, heh.

[smallpatch]

There are many types of maple, from silver to sugar.
Not sure about stiffness, but guaranteed sugar maple is harder than any cherry, and most walnut.
Walnut tends to be more pithy, and will chip out easily.
Cherry is very stable, and in the past, was used for levels for that reason.
Each obviously has its own merits.

So is walnut stiffer in compression, or tension?  Maybe better for bows?

[JCurtiss]

I'm surprised at how flexible cherry appears to be, given its hardness. For comparison, aluminum has an elastic modulus of   69GPa and mild steel is 200GPa!

[KNeilson]

I have good experience with metals but much less with wood. When I read the paper I saw a advert for a measuring tool, claiming that if you were to use it you`d be able to put a number to what an experienced person is capable of with just their body. That is he puts a dent in it and looks at a dial for distance and pressure....I see the thumbnail test mentioned round here for the same thing. I gotta admit I adopt it for making a selection sometimes. Also Flexed a  piece before too to test for "Youngs modulus"..Hefted for weight/density.   I think it still boils down to knowing what you need, which experience teaches,  Then you can go hunting for material that will suit them. If you have a need to record,anylize,compare and then communicate information with others a device like this becomes more important.
alloys of metal   vs  boards of different trees

[rich pierce]

http://www.wood-database.com/
There are many other sources online. Remember they present averages. You and I know there's a lot of variability from stick to stick.

[smart dog]

Hi Jim,
I beg to differ. The chart in the following link is much more in line with my experience using many of those woods.

http://workshopcompanion.com/KnowHow/Design/Nature_of_Wood/3_Wood_Strength/3_Wood_Strength.htm

dave

[Boompa]

Maybe it's just me but maple has always seemed harder than walnut on any stock I've worked with. Generally, black walnut in is softer. English walnut is better with it's more dense grain.  At any rate, I want a good hard piece of lumber for a stock, the softer stuff is too unpredictable.

[Mike Brooks]

I guess I've been wrong all these years. I thought red and sugar maple were harder than walnut and cherry....who would have guessed that?

[rich pierce]

From http://www.wood-database.com/


Common Name(s): Hard Maple, Sugar Maple, Rock Maple
Scientific Name: Acer saccharum
Average Dried Weight: 44 lbs/ft3 (705 kg/m3)
Specific Gravity (Basic, 12% MC): .56, .71
Janka Hardness: 1,450 lbf (6,450 N)
Modulus of Rupture: 15,800 lbf/in2 (109.0 MPa)
Elastic Modulus:  1,830,000 lbf/in2 (12.62 GPa)
Crushing Strength: 7,830 lbf/in2 (54.0 MPa)

Common Name(s): Red Maple
Scientific Name: Acer rubrum
Average Dried Weight: 38lbs/ft3 (610 kg/m3)
Specific Gravity (Basic, 12% MC): .49, .61
Janka Hardness: 950 lbf (4,230 N)
Modulus of Rupture: 13,400 lbf/in2 (92.4 MPa)
Elastic Modulus:  1,640,000 lbf/in2 (11.31 GPa)
Crushing Strength: 6,540 lbf/in2 (45.1 MPa)


Common Name(s): Black Walnut
Average Dried Weight: 38 lbs/ft3 (610 kg/m3)
Specific Gravity (Basic, 12% MC): .51, .61
Janka Hardness: 1,010 lbf (4,490 N)
Modulus of Rupture: 14,600 lbf/in2 (100.7 MPa)
Elastic Modulus:  1,680,000 lbf/in2 (11.59 GPa)
Crushing Strength: 7,580 lbf/in2 (52.3 MPa)
Shrinkage: Radial: 5.5%, Tangential: 7.8%, Volumetric: 12.8%, T/R Ratio: 1.4

Common Name(s): Black Cherry, Cherry, American Cherry
Scientific Name: Prunus serotina
Average Dried Weight:  35 lbs/ft3 (560 kg/m3)
Specific Gravity (Basic, 12% MC): .47, .56
Janka Hardness: 950 lbf (4,230 N)
Modulus of Rupture: 12,300 lbf/in2 (84.8 MPa)
Elastic Modulus:  1,490,000 lbf/in2 (10.30 GPa)
Crushing Strength: 7,110 lbf/in2 (49.0 MPa)

[Acer Saccharum]

I let my chisels tell me what's harder. 

Thanks, Rich, for the science.


I've had walnut that's as dense and hard as sugar maple, but it's not the norm. I've also had walnut that is not as good as poplar.

[PPatch]

I am in the last stages of finishing a walnut stocked rifle whose name is "Trouble" because of how that walnut fought me all the way. In the butt area it is as dense and tough as ebony yet it splinters and chips out if you look at it sideways. Chisels and gauges just skate off of it no matter how sharp, rasping it is murder and just dug out hunks so I had to give that up. I should have burnt that sucker. This is one of those projects that went to $#*! and stayed there, everything having to be done twice or three times.

I got sucked in because of the beautiful figure in the butt area:



At about this point I knew there was no chiseling happening


So I get clever with a jap style saw


And that caused no end of grief


But she is near completion


Besides Trouble, I call her my kinda sorta Southern Mountain rifle.

[WadePatton]

Thanks for the reminder of how difficult Pretty can be. 

[JCKelly]

Thanks, Rich, for the Real information.

I erred in posting essentially an ad for a test machine.

Did get a lot of good response, though.

Guess I should stick to metal.

[Carl Young]

Might find useful information in this book (https://archive.org/details/woodaircraftinsp00fore), I last read it ~30 years ago while repairing a Bellanca Viking, so I don't remember the specifics...

[jerrywh]

 I don't think it is that simple. There are a lot of different kinds of Walnut and maple. But I agree than the best walnut is much better than the best maple.

[Dphariss]

I have had my hands on a lot of walnut hundreds at least. The only ones I ever worked that I thought were as hard as good hard maple or close, were two Bastogne walnut blanks I got from Don King years ago.
They were nicely curly as well.

Dan

[James]

I don't think it is that simple. There are a lot of different kinds of Walnut and maple. But I agree than the best walnut is much better than the best maple.

Yes. and wood is not steel.  The hardness, strength etc... of steel is repeatable.  Wood on the other hand is technically one of a kind.  Each tree being shaped by where it stands makes any lab measurements nothing more than broad generalizations.

[Mike Brooks]

I have used alot of walnut like that over the years. It will put up a good fight!

[jerrywh]

 How many different kinds of walnut are there. I know I can't work with black walnut because of an allergy I have to it.  I can work with English walnut. I have had red Maple that was very soft and light. I couldn't even make a stock out of it. again I had some red maple that was almost as hard as Eastern maple. Same goes for some walnut.  Spec can be very misleading.
 For example you could say that the murder rate has gone up 100% while at the same time there were only 2 murders in the town of 50,000.  Twice as hard doesn't mean it is very hard wood. ETC.  I just judge each piece of wood as an individual. My favorite wood is still English walnut but you can't just say send me a piece of English walnut. If there is any wood that you will do best at by ordering sight unseen it is Eastern maple in my opinion. But it is more brittle for carving.
  I have learned that the art of picking out good wood is something that is not easy to learn.
 I wished I was as good at it as Ron Scott. That guy is a master at judging wood for gunstocks. You can't do master grade carving on bad wood. 

[Acer Saccharum]

I, too, find myself allergic to Black Walnut, especially dust. No problem with English. I took Jerry's recommendation for English for carving, and find it carves just incredibly well. Sugar maple takes excellent detail, but one needs to pay attention to the road so you don't accidentally pop a chip in the wrong place.