Wood Destruction testing and results!

I work with tons of Rosewood (about 500# of various species currently in my collection) and numerous other exotics. Tubi is particularly impressive. Grows only in one spot on the Solomon islands, polishes like plastic, sinks like a stone in water, and is damn near as hard as lignum vitae. It's more like aluminum than most woods.

Anyways, I've never had a piece of Rosewood, Macassar ebony, tubi, katalox, canary wood, ect blow up on the table saw. And I've only seen Nigerian ebony do it once, and that was a cracked piece.
I've had several chunks of stabilized burl blow to bits on the tablesaw. Using a fine tooth crosscut blade instead of a rip blade helps, but isn't perfect.
 
Geoff Flato said:
I work with tons of Rosewood (about 500# of various species currently in my collection) and numerous other exotics. Tubi is particularly impressive. Grows only in one spot on the Solomon islands, polishes like plastic, sinks like a stone in water, and is damn near as hard as lignum vitae. It's more like aluminum than most woods.

Anyways, I've never had a piece of Rosewood, Macassar ebony, tubi, katalox, canary wood, ect blow up on the table saw. And I've only seen Nigerian ebony do it once, and that was a cracked piece.
I've had several chunks of stabilized burl blow to bits on the tablesaw. Using a fine tooth crosscut blade instead of a rip blade helps, but isn't perfect.
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Worst i ever saw was when i was working at a high end wood shop. We had a new guy who didnt know one of the rules. Never put cracked wood through the jointer. Guy came in with an ANCIENT piece of wenge, right through with cracks and pin holes. Newbie takes it to the massive 8hp jointer "Actually original to the shop! 1947! We wore through the cast iron fence. Wore right through it!" and all i hear is BANG. Like a gunshot went off. The blade caught in a split and hurled the thing backwards at break neck speed where it then EXPLODED and shot those damn wenge needles everywhere. Not a fun day to sweep up.
 
That sounds quite unpleasant.... I've had the jointer blow up a few pieces as well. Usually something where it's my fault for it being too heavily figured or not paying attention to the grain and running it through the wrong way. I've mostly stopped using the jointer for exotics, the tablesaw and disc sander will handle most of it for knife sized stuff. Still gets used a ton for other projects though.

Would that jointer have happened to be an Oliver? Sounds like pattern shop equipment to me. I'm a bit of a vintage tool and machinery collector, apart from the grinders, mill, and lathe, everything in my shop ranges from the 1890s to the 1960s
 
Remember that improper drying may introduce very high stresses !! This can happen if you put a 4" piece of wood in a kiln set for a 2" schedule ,for example.
Another illustration of wood stresses is a rifle with a very powerful cartridge .Rifle stocks are usually walnut but the fanciest figured woods are avoided for the most powerful
cartridges because those woods may crack easier !
Another example is damage done to ebony for musical instruments .Finding this wood was shattering when machined was found to come from areas where brush was removed around the trees by burning ! I assume this was from micro-cracks from the heat of the fires !
 
mete said:
Remember that improper drying may introduce very high stresses !! This can happen if you put a 4" piece of wood in a kiln set for a 2" schedule ,for example.
Another illustration of wood stresses is a rifle with a very powerful cartridge .Rifle stocks are usually walnut but the fanciest figured woods are avoided for the most powerful
cartridges because those woods may crack easier !
Another example is damage done to ebony for musical instruments .Finding this wood was shattering when machined was found to come from areas where brush was removed around the trees by burning ! I assume this was from micro-cracks from the heat of the fires !
Click to expand...

Luckily even improperly dried wood will equalize if it hasn't introduced major cracking

And in the case of the ebony, that's an interesting idea. In my experience at least ebony is up there with snakewood and green desert ironwood as one of the most difficult woods to dry. Ebony is just DYING to crack on you.
 
How about twisting strenght?
I mean a hidden tang epoxied in a block of wood and after curing turn the handle (belly to spine)
 
Interesting results anyway. I think all 4 make great handles. Even unstabilized black walnut makes a good handle.

Really, the only wood I see in common use, and use myself, that I'm unimpressed with as far as durability, is quilted redwood. Not the burl-veiny-eye redwood, that all seems rather dense and hard, but the stuff that looks like quilted maple or compression koa. That stuff is like pine or spruce it seems. Even stabilized it's very easy to cut and work.
 
Surely when people talk about "only using stabilised wood" what they are really talking about is comparing stabilised wood X with unstabilised wood X. A better test would have been between stabilised maple and unstabilised maple. I have heard walnut doesn't take stabilising well, not sure if that is true, but the bits I have had that were sold as stabilised aren't really all that dense, not compared to maple, ash, birch or redwood. For an even clearer test, compare stabilised box elder burl with unstabilised box elder burl.

Also, isn't the main interest isn't how well a knife holds up if thrown off a building, but how it holds up if dropped on a rock from chest high? I was showing my neighbour's dad a nearly finished knife with a oil finished curly walnut handle and he dropped it butt first on the rough concrete path and managed to chew up the edges of the flare. Don't know if the added compression strength gained from stabilising would have helped (esp since this was walnut again) but it might have.

The variability of how the blocks hit the ground might play quite a part in how the wood held up. Landing on corners first will have been a lot harder than landing on a flat and bouncing onto corners.

If I was doing a test like this, I think I would probably make up a hinged arm with the option of adding weights, and an "anvil" that I could put different things in for the wood to hit. Could then alter the angle the wood hit the anvil, all samples would hit the same thing in the same way at the same speed. Samples could be smaller since the weight of the sample wouldn't matter like it does when dropped off a great height....wouldn't get anyone fit like climbing stairs though! :D

Thanks!

Chris
 
I appreciate the work you did for your test, but there is a huge factor. The impact itself. That is the one thing you can't control in a drop test.

I recently helped my 1st grade daughter do a science experiment on meteorite impact. We put out a bucket of sand and basically dropped rocks, and chunks of steel from various heights. Each result was different. Some were much deeper, others more shallow. The rock face that made the impact was the critical factor. The sharper ends helped the rock go deeper.

I am only telling you this, because drop testing in terms of a scientific experiment is flawed. If the piece happens to land flat, the impact will be absorbed very different then an edge, or corner impact. I would be interested if you could simulate the same experiment with a controlled impact, like hitting the same spot on the wood with equal pressures.

Stabilized does make the wood harder, as as well all know here, hardness = more brittle. Kind of turns the wood into plastic which is brittle.
 
I've found a few woods to move some shrinkage wise if they haven't been seasoned long enough. I've got the biggest hardwood supplier in western Canada about 5 minutes from my shop, so I'm there every couple weeks picking through the new arrivals. My usual rule is that apart from the Nigerian ebony and Pao Ferro (aka Bolivian Rosewood even though it isn't a true Rosewood, one of my favorites) which have always been well seasoned and very stable from them (a lot of the ebony has been in stock for 10 years or more, and Pao Ferro won't move no matter what you do). Anyways, I'll let new arrivals sit in my shop for at least 2-3 years before I'll start using them. I've found this greatly cuts down on movement, and has completely eliminated a handle shrinking after installation and requiring a slight reshape on the belt grinder to make everything flush again.

The problem with this is that you need a huge pile of wood in stock, and still have to buy as fast as you use it. But I love looking through hardwoods, and probably have close to a ton of various species currently piled up around the shop.
 
C_Claycomb said:
The variability of how the blocks hit the ground might play quite a part in how the wood held up. Landing on corners first will have been a lot harder than landing on a flat and bouncing onto corners.

Thanks!

Chris
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Damn, you beat me too it.
I like your idea. A swinging arm with a weight on it, with the piece firmly attached. Keep the controls the same, and that will give you more accurate results.
 
nateman_doo said:
I appreciate the work you did for your test, but there is a huge factor. The impact itself. That is the one thing you can't control in a drop test.

Stabilized does make the wood harder, as as well all know here, hardness = more brittle. Kind of turns the wood into plastic which is brittle.
Click to expand...

I did consider the impact angle of course. I tossed the blocks with a high spin, and the lack of any scuffing, marks or damage on the flat faces tells me that few to none of the impacts occurred on the faces, which makes sense when you consider there are many more ways t hit on a corner and only a single way to land perfectly on a face. This experiment was not designed to be a perfectly scientific test of wood strength under dynamic load. It was to test the rough durability of wood in a very extreme test, and to see if there is a real gap between the strength of exotic wood and stabilized wood. For a purely scientific test i would have to use perfectly straight grained blocks of wood, but would that be of any use to knife makers? How many of you use straight grained maple or walnut for your knives?

And stabilized woods are actually harder and tougher. The acrylic monomer that is used in impregnation helps increase the toughness in several ways, the most important being to strengthen the bonds between fibers. Wood is transversely isotropic, meaning two planes are functionally identical with a 3rd differing plane "Face grain and edge grain to end grain" and by strengthening the bond between the fibers, normally the job of ligand, the woods shear strength is greatly increased. Look at the results. None of the blocks suffered major fiber damage, IE splitting as though from a cross cut. They had pieces break out the long way, along the bond of the grain.

Woods like cocobolo and rosewood have a LOT of ligand, one of the main reasons they are so strong. The stabilizing processes acts like additional ligands, bonding the fibers together and making them more resistant to separation.
 
I don't have wood stabilized for durability or strength. I have it done for stability and ease of finishing. Some woods ( DI, Cocobolo, AB) don't need stabilization because they are inherently stable and easy to finish.
Early on in my knife making journey, I made several paring knives out of ATS-34 and several different natural hardwoods including Cocobolo, DI, AB, Osage/Bois D' Arc, Bocote, etc.. I glued em up with Acraglass and used straight pins (no head) and intentionally ran them through the dishwasher repeatedly for 5+ years. They don't look very nice but they are all still functionally sound.
 
Darrin Sanders said:
I don't have wood stabilized for durability or strength. I have it done for stability and ease of finishing. Some woods ( DI, Cocobolo, AB) don't need stabilization because they are inherently stable and easy to finish.
Early on in my knife making journey, I made several paring knives out of ATS-34 and several different natural hardwoods including Cocobolo, DI, AB, Osage/Bois D' Arc, Bocote, etc.. I glued em up with Acraglass and used straight pins (no head) and intentionally ran them through the dishwasher repeatedly for 5+ years. They don't look very nice but they are all still functionally sound.
Click to expand...
That sounds similar to my experience. I did a chefs knife for a family member a few years ago. Aeb-L stainless, straight pins, handle glued on with hysol e120hp. Last time I was out there I noticed it had been ran through the dishwasher for the last few year's. Doesn't look very good, but it's still in one piece
 
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