Drop Angle

[Bill_Melater]

Recently I was asked why I like Khukuri, I couldn't give an answer other than "I've used them, I like them".

Given that Khukri are on the chopping end of blade design and they do remarkably well on this front but there are many good choppers out there without a drop angle, some even swept backwards. Even from the perspective of being able to better select a Khukuri for a desired task, I was wondering what if any effect, the drop angle actually has on how the khukuri will perform or if there is much more to it than that.

For example, contrast a Falo with an Ek Chirra if we stay in the Kailash family. Of if you prefer, take an Ek Chirra as is and a theoretical one completely the same but with a straight spine.

 

[Kailash Blades]

It's a complicated point that I would say doesn't have a consensus on yet. Some good discussion on edge angle in relation to axes here including the comments:
Some potential benefits:
-An outwardly curving blade profile has a tendency to convert a chop into a draw cut- sliding across the target as the cut moves through it's course. A inwardly curving blade profile (khukuri) has the opposite- a tendency to grab, snag and bite deeply.
-get the wrist into a more stable and stronger position while chopping (this can be done through handle cant alone though)
-Helps to ensure that in hard chopping the edge is coming into the material perpendicularly (some particularly sickle like khukuri curve so much as to go past perpendicular)
-fits in more edge length and weight of steel per inch of overall blade (can be said of outwardly curving blades eg sabres as well though)
-potential interactions with shields? Chopping into the edge, grabbing and pulling the edge towards you, cutting past the edge.
-striking at higher targets eg mans head, neck, shoulders as discussed in above video.

These potential benefits are outweighed by:
-poorer tip alignment for thrusts.
-heavier blade per inch in terms of reach.
-arguably less intuitive cut placement.

This analysis of potential benefits of a blade style is limited in how useful it is. We don't know how many if any of these characteristics were valued historically when developing the blade style. It could be that some of these characteristics were vestigial from prior forms of the blade (eg sickle or agricultural tool).
Take care,
Andrew and the team at Kailash

 

[scdub]

Excellent response. One note however - I believe you’re looking for a word like “counterbalanced” rather than “outweighed”.

These potential benefits are outweighed by:

 

[Kailash Blades]

Ah yeah sorry- was eating breakfast while typing. The benefits are exchanged for drawbacks i mean.

 

[Chandra]

Recently I was asked why I like Khukuri, I couldn't give an answer other than "I've used them, I like them".

Given that Khukri are on the chopping end of blade design and they do remarkably well on this front but there are many good choppers out there without a drop angle, some even swept backwards. Even from the perspective of being able to better select a Khukuri for a desired task, I was wondering what if any effect, the drop angle actually has on how the khukuri will perform or if there is much more to it than that.

For example, contrast a Falo with an Ek Chirra if we stay in the Kailash family. Of if you prefer, take an Ek Chirra as is and a theoretical one completely the same but with a straight spine.

IMO, your initial response of you liking Khukuri is enough. I don't see the need to defend/justify a personal preference. Regardless of what kind of tool it is, what makes a good chopper is a forward balanced blade.
Drop angle is not the only thing that affects how a blade performs. The overall weight, balance, edge geometry, sharpness, length, etc. all factor in.
Andrew has very nicely detailed the pros and cons of severe drop angles.
I just want to add that a severely curved blade affects it's utilitarian function. Think about chopping firewood while crouching/sitting down, or chopping a small tree at its base. In both scenarios, you will be forced to awkwardly adjust your own position, rather than you positioning the blade and working comfortably.

Also, take into account the handle curvature, as this too affects the overall curve of the Khukuri.
This is one of the reasons why shorter (10"-12") "Sirupate" style Khukuris are more popular in Nepal. A lot of work here (at least in the rural areas, people in cities don't EDC Khukuris) is done squatting down. Also, axes are used to fell trees, so the average villager does not usually carry a 15" large Budhuna or Salyani style Khukuris.

 

[bigeard09]

IMO, your initial response of you liking Khukuri is enough. I don't see the need to defend/justify a personal preference. Regardless of what kind of tool it is, what makes a good chopper is a forward balanced blade.
Drop angle is not the only thing that affects how a blade performs. The overall weight, balance, edge geometry, sharpness, length, etc. all factor in.
Andrew has very nicely detailed the pros and cons of severe drop angles.
I just want to add that a severely curved blade affects it's utilitarian function. Think about chopping firewood while crouching/sitting down, or chopping a small tree at its base. In both scenarios, you will be forced to awkwardly adjust your own position, rather than you positioning the blade and working comfortably.

Also, take into account the handle curvature, as this too affects the overall curve of the Khukuri.
This is one of the reasons why shorter (10"-12") "Sirupate" style Khukuris are more popular in Nepal. A lot of work here (at least in the rural areas, people in cities don't EDC Khukuris) is done squatting down. Also, axes are used to fell trees, so the average villager does not usually carry a 15" large Budhuna or Salyani style Khukuris.

Hi Chandra , would definitely agree regarding over or severely curved blades and the fact in some usage they can be a hinderance ! Also as you said the weight verses balance verses edge geometry verses overall ergonomics is all important in choosing the right khukuri for the right job and in my opinion this is where Andrews strength lies as he does seem to understand the whole process of what a khukuri is and its usage . I understand its horses for courses and many collectors / users prefer longer / larger style khukuri but I also see the advantages of using a smaller <13" blade for many of the camp / bushcraft / utility tasks .

 

[Bill_Melater]

Just to add a bit of closure to this, I did a bit more digging and much in line with Andrew's post, Matt Easton actually had a video on the topic:

Why do Forward Curved Blades Cut So Well?

TLDR: blades that curve back are good for pull pull cuts and getting away, forward curves do more of a push cut and bite in. Add the forward balance and you get a more powerful chop but interestingly enough, that weight also helps with having proper edge alignment.

Someone correct me if I'm wrong; but this seems to say that if heavier chopping is your goal, a model with a more drastic drop angle is your go to (without getting into the weeds of thickness, edge profile, and other still important factors). A straighter spine might maximize reach/tip speed and be more suited for brush clearing. All of this is being framed around the idea: "I want a khukuri, but I don't know what kind to get first" (because you can't just have one).

Disclaimor: I'm no expert bushcrafter, I'm just the curious sort who thinks too much about some things.

 

[Bill_Melater]

IMO, your initial response of you liking Khukuri is enough. I don't see the need to defend/justify a personal preference. Regardless of what kind of tool it is, what makes a good chopper is a forward balanced blade.
Drop angle is not the only thing that affects how a blade performs. The overall weight, balance, edge geometry, sharpness, length, etc. all factor in.
Andrew has very nicely detailed the pros and cons of severe drop angles.
I just want to add that a severely curved blade affects it's utilitarian function. Think about chopping firewood while crouching/sitting down, or chopping a small tree at its base. In both scenarios, you will be forced to awkwardly adjust your own position, rather than you positioning the blade and working comfortably.

Also, take into account the handle curvature, as this too affects the overall curve of the Khukuri.
This is one of the reasons why shorter (10"-12") "Sirupate" style Khukuris are more popular in Nepal. A lot of work here (at least in the rural areas, people in cities don't EDC Khukuris) is done squatting down. Also, axes are used to fell trees, so the average villager does not usually carry a 15" large Budhuna or Salyani style Khukuris.

Well, it wasn't so much that I needed a justification as it was that it bothered me that I didn't actually know how they worked.

Interesting that the 10"-12" are the most popular. As I use mine I'm starting to find that to be the sweet spot. I've got a 14" hopefully on the way soon (don't worry, I'm patient) and so we'll see if I find it too long or not. But I have a 10" model that is no slouch when it comes to chopping or being a good camp knife but it does suffer when dealing with lighter whippy things.

Obvously a Khukuri isn't a replacement for an axe so I am aware some of this discussion does get pedantic.

 

[Crusty_Otter]

I've always though of the forward canted blade, either curved or angled, as a force multiplier during the swing. The edge will make contact with the target earlier than it would with a straight, western style blade. Now add in the additional forward weight of the khukuri and, to me at least, it translates to a more efficient blade requiring less effort to get the same results.

I'm definitely new to khukuri use but, being a smaller framed guy (5'-9", roughly 150 lbs), and feeling my age (57) and old injuries more these days, a more efficient blade means I don't have to wear myself out as much to get the same results.
Jack

 

[Kailash Blades]

I've seen this Matt Easton video and agree with his comments in general. (your link sends back to this thread here is an adjusted version.)
However I don't agree with the assertion that having the edge forwards of the handle axis helps with cut alignment due to gravity. He says that this part "hangs" down so helping to align the blade for vertical strikes, chops etc. The problem with this is that correct edge alignment even with axes is rarely vertical and also that this "hanging' force is quite low compared to the accelerations involved in swinging a khukuri or axe.

I do think that it helps with edge alignment though, just by a different mechanism:

-For the sake of this point we can simplify a longsword down to a broom handle. There is even weight on all sides of the handle axis so it doesn't want to hang from gravity or twist when accelerated by the arm.

-Let's take that same pole and stick a 50cmx50cm "flag" of thick steel sticking downwards to simulate the forwards weight of a khukuri/axe head. Under gravity this hangs downwards. Let's say we hold the broom handle straight out in front of us and then swing it horizontally to the left as hard and quick as we can. In this situation the "flag" will tilt to the right, with the handle leading the way. This is because the centre of mass is now not in line with the handle axis. When we move the weapon it wants to trail behind, like we're dragging it through the air. This force actually works to fight edge alignment and reverse the blade. However this force does provide crucial feedback to the user. The tilting force will be at its lowest when the blade is aligned in the direction of the swing. The centre of mass is traling "back into" the spine of the blade itself. If it was held at 90 degrees to the direction of swing here the tilting force would be at its maximum. It has the most torque to spin the handle and none of the force vector is going back into the blade. This helps a user to tell if the blade is aligned or not and is a force which is absent form symmetrical blades like longswords. These often rely on oval shaped handles instead for feedback, where non symmetrical blades can often use round handles and cope just fine.

-We've discussed a blade with the centre of mass forward of the handle axis but what about behind it? Reversing our flag now represents sabres, shamshir, dusack, katana, dha etc. Here the centre of mass is behind the handle axis which is where it wants to be. In this instance the trailing effect is self stabilising and actually does align the edge. When the edge is unaligned the hand also feels a turning torque which is useful feedback. Note that they all feature edge profiles that curve outwards, biasing them more to slashing and draw cuts.
Can anyone think of a blade style which has both this trailing centre of mass for alignment AND an inwards curving edge to accentuate chopping performance?

I've always though of the forward canted blade, either curved or angled, as a force multiplier during the swing. The edge will make contact with the target earlier than it would with a straight, western style blade.

I've heard this said a few times, but have never really understood it. How does earlier edge contact amplify force or increase strike power? Maybe you can help me understand the viewpoint.

 

[meboz]

Can anyone think of a blade style which has both this trailing centre of mass for alignment AND an inwards curving edge to accentuate chopping performance?

Wouldn't normal sickles / hand scythes and swords styled like that fit that description?
I feel like I've seen some swords with a distinct normal/agricultural sickle shape, but I don't recall if they were just "fantasy" swords or actual historical styles.

 

[Crusty_Otter]

I've heard this said a few times, but have never really understood it. How does earlier edge contact amplify force or increase strike power? Maybe you can help me understand the viewpoint.

Maybe it's just me, and it's possible that it's just a matter of getting used to the characteristics of a khukuri being more weight forward in balance, as well as the point of contact being lower in relationship to the handle, compared to similarly sized straight western blades and their neutral balance. Khukuri seem to have an advantage in momentum during a swing. As far as earlier edge contact being a multiplier, I guess the best way I can describe what I mean is in terms of a bat swing: you can swing AT the ball, targeting the surface and get a hit, or swing through the ball and get better results. The point of contact being earlier when swinging a khukuri "feels" like it's still got more momentum behind it, helping carry the blade further into the target.

It may just be a matter of experience: a straight blade will make contact at roughly the same point in a swing every time, relative to the hand position in the arc of that swing. With lifetime of that experience, swinging a khukuri with it's earlier point of contact means hitting the target when you'd usually still be applying force to the swing of a straight blade, so it's more like swinging "through" the target than "at" it.

As far as edge alignment and accurately placing hits, with my limited use I've noticed I'm impacting exactly where I intend to with my Ek Chirra, both on the target and on the belly of the blade. It actually seems like I'm more accurate with my khukuri than I am with my heavy western chopper, a SwampRat Battle Rat (OAL: 14", blade length: 9.5", thickness: .25" with Ø distal taper, a saber grind and weight of 482 grams). My 11" Ek Chirra weighs 610 grams with the full tang, micarta handle and steel hardware but, somehow, it feels lighter in hand. I'm not even going to try to figure that one out.
Jack

 

[Crusty_Otter]

Wouldn't normal sickles / hand scythes and swords styled like that fit that description?
I feel like I've seen some swords with a distinct normal/agricultural sickle shape, but I don't recall if they were just "fantasy" swords or actual historical styles.

Sickle swords, like the kopesh, did exist at one time but I believe they were sharpened along the outer, convex side of the curve.
There are/were polearms that used an inwardly curved edge, like the halberds carried by Vatican Swiss Guards, but I have no idea how they're balanced as far as center of mass. They definitely look like they could hook, grab and pull but as far as chopping characteristics, that sounds like a question for Matt Easton.

 

[Bill_Melater]

Maybe it's just me, and it's possible that it's just a matter of getting used to the characteristics of a khukuri being more weight forward in balance, as well as the point of contact being lower in relationship to the handle, compared to similarly sized straight western blades and their neutral balance. Khukuri seem to have an advantage in momentum during a swing. As far as earlier edge contact being a multiplier, I guess the best way I can describe what I mean is in terms of a bat swing: you can swing AT the ball, targeting the surface and get a hit, or swing through the ball and get better results. The point of contact being earlier when swinging a khukuri "feels" like it's still got more momentum behind it, helping carry the blade further into the target.

It may just be a matter of experience: a straight blade will make contact at roughly the same point in a swing every time, relative to the hand position in the arc of that swing. With lifetime of that experience, swinging a khukuri with it's earlier point of contact means hitting the target when you'd usually still be applying force to the swing of a straight blade, so it's more like swinging "through" the target than "at" it.

As far as edge alignment and accurately placing hits, with my limited use I've noticed I'm impacting exactly where I intend to with my Ek Chirra, both on the target and on the belly of the blade. It actually seems like I'm more accurate with my khukuri than I am with my heavy western chopper, a SwampRat Battle Rat (OAL: 14", blade length: 9.5", thickness: .25" with Ø distal taper, a saber grind and weight of 482 grams). My 11" Ek Chirra weighs 610 grams with the full tang, micarta handle and steel hardware but, somehow, it feels lighter in hand. I'm not even going to try to figure that one out.
Jack

Your theory on follow through (if I can call it that) does make some of sense. But I also wonder if the downward curve also creates a hooking action that may more or less keep the target object pulled into the strike. Much like in Matt's video where he talks about creating a push cut into the target instead of a pull cut away. Withe better follow through this could be that "force multiplier" effect.

 

[Bill_Melater]

[Removed. Accidental post]

 

[Kailash Blades]

Wouldn't normal sickles / hand scythes and swords styled like that fit that description?
I feel like I've seen some swords with a distinct normal/agricultural sickle shape, but I don't recall if they were just "fantasy" swords or actual historical styles.

The khopesh has the right shape but I've also heard that they were sharp on the outward edge only. I've certainly seen them depicted with sharp inner edges in media though. Some examples I can think of are the Shotel, some Kondo and more recently the Woodsman's Pal (and similar billhooks). The general concept seems more common in african weapons.

Maybe it's just me, and it's possible that it's just a matter of getting used to the characteristics of a khukuri being more weight forward in balance, as well as the point of contact being lower in relationship to the handle, compared to similarly sized straight western blades and their neutral balance. Khukuri seem to have an advantage in momentum during a swing. As far as earlier edge contact being a multiplier, I guess the best way I can describe what I mean is in terms of a bat swing: you can swing AT the ball, targeting the surface and get a hit, or swing through the ball and get better results. The point of contact being earlier when swinging a khukuri "feels" like it's still got more momentum behind it, helping carry the blade further into the target.

It may just be a matter of experience: a straight blade will make contact at roughly the same point in a swing every time, relative to the hand position in the arc of that swing. With lifetime of that experience, swinging a khukuri with it's earlier point of contact means hitting the target when you'd usually still be applying force to the swing of a straight blade, so it's more like swinging "through" the target than "at" it.

As far as edge alignment and accurately placing hits, with my limited use I've noticed I'm impacting exactly where I intend to with my Ek Chirra, both on the target and on the belly of the blade. It actually seems like I'm more accurate with my khukuri than I am with my heavy western chopper, a SwampRat Battle Rat (OAL: 14", blade length: 9.5", thickness: .25" with Ø distal taper, a saber grind and weight of 482 grams). My 11" Ek Chirra weighs 610 grams with the full tang, micarta handle and steel hardware but, somehow, it feels lighter in hand. I'm not even going to try to figure that one out.
Jack

It's tricky stuff isn't it? I am still trying to figure it out from some good resources online but it seems you have to have a good formal, fundamental understanding of physics in order to parse a lot of it. I have a good scientific mind but struggle a bit with these texts. Length, overall mass, mass distribution, and speed are all important for the momentum advantage being described. Sometimes blades can "feel lighter" in the hand. This to me is usually a sign that the POB is closer to the hand, so the weight is resting more in the hand rather than levering on it. It can also sometimes "feel lighter" in motion or when accelerating. This I feel usually described a blade with low rotational inertia. It can have the same POB, but the tip and back of handle are lighter weight (often due to rat tail tang or distal taper) meaning that it's easier to get the blade rotating or stop it from rotating in your hand.

I understand what you're saying about the earlier impact point. I think that maybe it's better described less as a force multiplier and more of a biomechanical advantage in the way that the blade interfaces with the human body. I'm not sure about it though- it sort of assumes that we don't have enough distance to follow through in the first place which is easily avoided. Likewise this follow through distance is being borrowed from the distance it takes to accelrate the swing up to speed which is more critical. I think that it allows you to make contact at a better, more stable and powerful feeling wrist angle which is a closely connected concept though. Whether or not the edge contacting earlier actually does make it easier to follow through on a target, if it makes you feel like you can follow through more easily then that's a big kinesthetic positive. It could be that I use so many khukuris that I don't really feel it but for people coming over from swinging baseball bats or straight knives it could be a widely helpful thing.

Your theory on follow through (if I can call it that) does make some of sense. But I also wonder if the downward curve also creates a hooking action that may more or less keep the target object pulled into the strike. Much like in Matt's video where he talks about creating a push cut into the target instead of a pull cut away. Withe better follow through this could be that "force multiplier" effect.

"-An outwardly curving blade profile has a tendency to convert a chop into a draw cut- sliding across the target as the cut moves through it's course. A inwardly curving blade profile (khukuri) has the opposite- a tendency to grab, snag and bite deeply." I covered this in my first point in different words. Perhaps not clearly.
I think this is a big benefit for hacking deeply into things and is great for chopping wood. I think this does have a limit to the utility in martial situations though as you eventually want the follow through of the blade to draw free of the target and follow up with another chop or even a thrust. A blade with extreme inwards curvature (kora, billhook style halberd, reverse edged falchion) is at risk of snagging in these instances. I think it's worth noting that the kora has no thrusting capability and the other to examples have more of a "swap from thrust mode then to chop mode" use style rather than a chop/slash into thrust more integrated style like the khukuri or yataghan.

Take care,
Andrew and the team at Kailash