Chopping Damage

M

me2

Joined
Oct 11, 2003
Messages
5,102
In a recent video of some damage while chopping, a participant referenced something called Unsupported Chopping Phenomenon. They mentioned some more information might be available from the Beckerheads. I'm curious about this phenomenon, and was wondering if anyone here has heard of it or experienced it when using their large choppers? I have not had the characteristic half moon fractures happen on any large blades I use, so cannot comment on it first hand. If anyone has had it happen, can you suggest a method for perhaps replicating it, just to give my large blades a test before taking them out of the back yard? The worst damage I've seen is some edge deformation from pin knots and an occasional accidental impact with a rock while cutting close to the ground. The kind of damage described is much more severe, extending well into the primary grind.
 
I think that "Unsupported chopping" means chopping without stabilizing the cant of the edge as it strikes. Basically not gripping the handle tightly enough to keep edge straight as it chops. This allows the edge to twist while in the media, which can cause a torsion break in the edge it self from lateral stress on a narrow portion of the blade. I could be totally wrong though. It wouldn't be the first time and wont be the last.
 
I had it happen on a Golok a few years back. I was chopping a fairly small branch on a dead Hemlock tree(very hard wood) i came away with just what you describe a halfmoon chunk missing out of the edge.

I'm told it comes from holding the knife too loosely in the hand. Allowing it to twist on impact.

That being said I have been chopping stuff with big knives since I was a kid and this is the only time it happened to me. Once in forty-five years in extremely hard dead Hemlock.

I do not know what if any influence edge geometry and hardness has on the phenomenon.
 
Yeah,

What Silverthorne said! I missed his post,

Not sure about the Jock-Strap part.

But it couldn't hurt, maybe out of Kevlar in case of a bad swing.
 
it can happen if you're chopping into twisted grain -- like a knot or a fork -- when the thing you are chopping into moves as you're cutting, which can make the knife twist in the cut as you're pulling it back out (on the off chance you didn't cut all the way through)
 
As it was described, I dont think a hand can hold a large knife steady enough. Also, as it was described, any knife can suffer from this phenomenon, regardless of geometry or wood type.

What type of golok was it? Were you able to get a locally made leaf spring version? I've always liked those, though I've never been anywhere to get one.
 
Correct me if I am wrong but if the blade shears like its got a bite out of it, is this not a heat treat issue? IE if the blade drifts in the wood then it should bend, not break. Ideally it should spring back after the bend.

Have had an issue with machetes bending because of drifting with the wood grain. Basically the edge follows the wood grain and combined with the force of the chop it bends out the edge. Also have had just bad swings that deflected causing the edge/blade to bend all together.

The half moon issues has to do with torsional rigidity. Either its bending at the edge, basically meaning the buried edge is the source of the torsion, or its from the spine/handle.

Either way I dont think you could feasibly replicate this to satisfaction without damaging the blade or yourself.... You could try to weak hand chop with a loose grip, or chop then pry the edge to the left or right, but I dont know if you will actually accomplish anything.

You can test your blades in the backyard but nothing can account for the unknown, and even at that, how are we even sure that the "testing" or "proving" is not the actual cause of some failures later in blade life. Micro cracks, fractures and all that forming because of some testing methodology applied to the blade. If it was me, I would just use the blade and go for it. If it can cut, slice, carve, and possibly split, then its going to do just fine for reasonable expectations.

Good luck out there! ;)
 
actually, no -- I recently tore a chunk out of the edge on a chopper more than 1/4" deep, sent it back to the factory and the response from their metallurgist was "no flaw, no problem with heat treat, no sign of abuse -- sometimes stuff happens and your replacement is on the way"
at the time it happened, i was cutting down a honey locust and there was a hidden scar inside the tree i couldn't see until it dropped - so twisty grain, varying stresses, the target moving sode to side and front to back, and with all that going on I sincerely doubt I pulled the knife straight up and out of the cut channel.
roughly 3" tree - you can see the grain weirdness despite the lack of focus.
chip.jpg
 
There are a lot of good explanations as to the causes..I would just attribute it to Murphy's law. To combat Murphy's law buy a BK9 and tell Murphy to take a hike.
 
Without naming names, can you give more details on the chopper that lost a piece on the locust? Stuff like steel, hardness, edge angle, thickness, etc. That was a live locust when you started I assume from the pictures?
 
unsupported shopping phenomenon is also called Impulse Buying Syndrome, when you start buying knives based on looks without doing research










:D
 
there's also a thought that the half moon chips are similar to what happens to obsidian and the like...

locally induced fracture that radiates out to a certain distance and then POP

i wonder if there's a "speed of sound"* local issue, where if the metal's condition causes such impulses to be reinforced in the given medium

(remember, speed of sound, shockwaves, varies by medium)... certainly the impulse of the force has a speed, and the radius does suggest a shockwave damage effect.

just a thought i've had, as metal does have semi-crystalline properties on occasion :D
 
Bladite said:
there's also a thought that the half moon chips are similar to what happens to obsidian and the like...

locally induced fracture that radiates out to a certain distance and then POP

i wonder if there's a "speed of sound"* local issue, where if the metal's condition causes such impulses to be reinforced in the given medium

(remember, speed of sound, shockwaves, varies by medium)... certainly the impulse of the force has a speed, and the radius does suggest a shockwave damage effect.

just a thought i've had, as metal does have semi-crystalline properties on occasion :D
Click to expand...

Great, I feel more stupid now.....
 
Please! Numbers i can understand, they are constant.

Im not sure if your previous post is talking about knives or space travel :confused:
 
worldwood said:
Please! Numbers i can understand, they are constant.

Im not sure if your previous post is talking about knives or space travel :confused:
Click to expand...

no numbers today. too hot to think...

must super-cool first... i goto "the office" because they have a/c :>

and yes, it is. all things are kung fu when reduced to their basics :D
 
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