Forward angle and chopping

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killa_concept

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May 19, 2009
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So my question is pretty much to what degree (pun intended) the angle of the forward sweep of a kukri affects it's chopping ability. I know there are many other factors that come into play, but please consider this factor independently. I'd imagine that a more forward curvature aids in chopping, but I'm guessing it's a matter of diminishing returns: there has to be a point where you can have so much curvature that it begins to detract from the balance and simply begins to detract.

The most forward curved kukri I can think of is the boomerang, so I'm kind of wondering how well that chops. The reason btw, is because I'm been sketching up a personal design that I eventually want to special order at some point in the distant future :o
 
I originaly chose my M-43 kukri because of it's forward angle, which was enhanced even more by the downcurved handle.

I wsn't dissapointed either it chops FAR out of it's weight range.

I can't say how the Bommerangs perform for I have never handled one.
 
Killa,

I'm been sketching up a personal design that I eventually want to special order at some point in the distant future
Click to expand...

I'm in the midst of doing the same as well.
The 18th Century model and the forward curving khuk were the pairs that had that effect.
The bites they inflict are somewhat thickening up my ideas.

Having tested the Bonecutter and ASTK side by side, i was amazed just how well a curvy profile (BC) ease up so much on the chopping.
(Well, the weight on ASTK was another issue)

Hence i started to look at design of M-43, Ganga Ram, Samsher...etc that all shared that profile.

Any rendition already? Mine will come in a trench look. :D
 
The human wrist, holding a straight object like a dowel or a straight blade, presents the edge of a knife at an angle to the surface being cut.

With a khuk or bent blade, the knife, held normally, presents the edge at much closer to a 90 degree, straight on angle, allowing the edge to bite more directly on impact.

The heavy weight of the khuk drives the edge deep into the object being cut. A lighter, slashing blade might rely on thin edge geometry and a drawing cut, allowing more of the sharp edge to do the cutting.

For sheer chopping, weight and blade angle allows a khuk to chop better than most any other design, IMO. As you have observed, there are diminishing returns to too much angle, just as there is to too little.

Andy
 
Andrew Colglazier said:
As you have observed, there are diminishing returns to too much angle, just as there is to too little.

Andy
Click to expand...

Yes - this is precisely my point. I'm trying to figure out at what point the forward curvature ceases to be helpful and becomes detrimental. We see most kukris with a 30-35 degree forward angle from the spine. The more forward curved kukris (like the m43) might go up to about 45ish degrees. Now the extreme ones, like the boomerang, teardrop sirupati, and m43/hanshee hybrid are even more forward curved than that. I'm just curious if that level of forward curvature diminishes chopping power or somehow helps it
 
Andrew Colglazier said:
The human wrist, holding a straight object like a dowel or a straight blade, presents the edge of a knife at an angle to the surface being cut.

With a khuk or bent blade, the knife, held normally, presents the edge at much closer to a 90 degree, straight on angle, allowing the edge to bite more directly on impact.

The heavy weight of the khuk drives the edge deep into the object being cut. A lighter, slashing blade might rely on thin edge geometry and a drawing cut, allowing more of the sharp edge to do the cutting.

For sheer chopping, weight and blade angle allows a khuk to chop better than most any other design, IMO. As you have observed, there are diminishing returns to too much angle, just as there is to too little.

Andy
Click to expand...

So, if one wanted to increase the chopping power of a lighter bladed khuk like a Gelbu Special or Siru would increasing the curve help or hurt?
 
Like was said too much curve and it reduces the chopping.

I had a Boomerang and it chopped fine but wasn't nearly as easy on my hand as the ones with less angle.

Also I think a khuk that the main curve is closer to the handle is a better chopper.
 
Killa, on chopping differences. The top knife is my new 20" AK your are familiar with the middle blade,it your old M43 and the bottom one is my 12" CAK.
The AK has ~4ounces and about and inch of length on the M43 and is more weight forward with a more obtuse angle. Here's the difference chopping wise, not much! You need a little more force to get there with the M43 but you get to the same place that the 20" AK is going with just a little bit of guidance & gravity. Handling wise they are 2 totally different animals the AK is sluggish but the M43 is livelier.
 

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Here's an approximation that allows for the variable physiology of users:

If you take a straight bladed chopper like, for example, the Martindale No. 2 golok, and extend the blade in front of you as if you were chopping, and such that your forearm is parallel to the ground, the blade will be elevated at an angle, theta, above horizontal. That angle, theta, should be close to the optimal drop angle for a khukri in your hands (because the edge will be descending horizontally and in alignment with your forearm). Also, the angle theta + 90 deg will be the drop angle at which a blade fails to make any impulsive contact at all with a target material (because at theta + 90 the edge is descending vertically).

For me theta is about 40 deg and I find the drop angle of the M43 most comfortable. Of course this ain't rocket science, just a crude approximation. :D
 
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Thanks for all the help guys - really great stuff that I'll definitely be factoring into my idea.

@hollowdweller thank you for the personal experience - that's exactly what I was wanting to find out. I'm guessing that too much curvature and you're arriving at the target at too much of an angle and too soon into your swing. The overly forward weigh would probably throw off the balance and feel as well.

@Andrew Your explanation makes pretty good sense. At extremes of curvature, you're probably starting to get to where the "sheering effect" caused by the angle turns more into a slicing one (as with a scythe or something)

@ oldschool and Cpl. I find it kind of amusing that you two have completely opposite opinions on the two designs. Chalk it up to different kamis/styles as well as personal preference I guess :)

@Bill I took some advanced physics and I'd much prefer crude estimations to that any day. Looking over my own blades and the kukri dynamics FAQ, I'd have to agree that past 40 degrees is probably where you start seeing diminishing returns
 
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Cpl Punishment said:
See, now, that's interesting.

My M43 feels like a brick, and my CAK feels livelier.
Click to expand...

Wow, "brick" is not usually a word that is associated with the M43, especially when it is being compared to village farm tool!!! It might be time to get the design back to the original size, where it is almost universally considered one of the best all around kukris ever designed.

Bill
Virginia
 
Don't get me wrong, it performs great. It just feels like dead weight in the hand.

Whereas my CAK -- which is longer and heavier -- feels "lively". Guess the M43 didn't choose me, eh? Must be something to that.
 
Maybe. ;)

Despite what it sounds like, I really do like it, though.

The only kukri I had that I really didn't get along with was the WWII, so it went to a new home. Hopefully the new owner likes it.
 
Cpl, I think my AK not being a chiruwa makes it more weight forward and less lively that if it had its weight distributed an inch or further back towards the handle.
My M43 isn't as nimble as my beloved machete's but its far from dead.
On a slightly different note. I slashed some water bottles last night. The M43 didn't hardly get me wet and the 20oz bottle was clean in half. The 20" AK did something weird. I probably didn't hit square or I hit with the tip and drug it. Think Spiral cut ham. That is 1 cut as fast as I can control it I couldn't do that with my pocket knife if I tried.
 

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