Reflection on big blades geometry

[Singularity]

As a resultant on my tests on big blades here and chopping, here is some reflection:

This explains why a khuk or a golok is vastly superior to a straight blade when chopping.
This does not take in account the convex edge which makes it even better.
Of course an experienced user will know how to saber, even with a straight blade. But the golock does it by design.
But for a lazy blow, or when you are tired, this is what happens. You also see what I called "handle axis" and edge over handle axis or edge under handle axis.

You can notice: there is much less length of blade that is (very) efficient on a khuk than on the golok, Therefore the precision with a golok is not that important.

You also undertand why the blade on the infamous French Guillotine is actually angled a 45 degrees, while it only does a push-cut. Right the shearing effect! 45 degrees angle on a blade can bring as much as 40 % better performance. These at least are the numbers for the Guillotine.

Now, this is why a Khukuri or a hatchet as Jimbo pointed me by email, is MUCH more dangerous:

Drawing explains the torque in handle as seen from behind the handle. The center of rotation is the center of the handle.
1: Straight blow, blade aligned with blow, Great!
2: Blade not aligned with blow, handle will try to turn. Forces of the blow tend to make things worst. The worst it gets, the more it wants to turn.
3: A Golok, edge behing or over handle axis, blade not aligned with blow. Forces tend to make things back to normal, as you pull the edge and not push it.
You can use a Khuk safely (but less efficiently) if you align the tip of the blade like the blade of the machete of drawing one , and thus maintain the handle below the edge.

Axis are in pink, original forces in red, impact forces in green.


Any thoughts / comments?

 

[Cliff Stamp]

It is nice to see some dicussion of these aspects, the shearing effect is often overlooked and you do want to take advantage of it for maximum benefit, see old posts in the HI forum for some discussion. However it is critical to remember that it is only one aspect of chopping ability, and not really a major one. Felling axes have upturned edges at the endpoints for a similar reason, as do chisels, as otherwise you will get wood splintering at the edge of the cut, instead of getting sliced. However it does not take much of a change in angle, edge thickness, balance or mass to swamp out these shearing effects.

A cheap machete for example, can easily match the penetration of a *much* more blade heavy khukuri because the machete has a much thinner edge cross section. The machete of course will bind readily, not clear out the wood naturally, nor be able to work it out because of a lack of stiffness. You can with straight blades such as machetes, initiate a draw on the chop, which will have a similar effect as the inherent slicing action due to the set of the blades on the khukuris. Edge angled profiles like recurves, or bolo designs will do the same thing, even though the spine is straight.

In regards to glances, these are caused when you change the angle of the swing. You should follow the same angle from the start to the finish. When you try to come in at a different angle than you intend to enter the wood, it takes a tremendous amount of skill to maintain the same angle in the wood, as it is a very short distance. The other major problem is coming in too shallow . The blade then clears the entire chip out and continues across the surface of the wood. Higher cutting blades are also far less prone to glancing as they penetrate deeper with less effort.

In regards to the Golok being safer than a hatchet, I can't remember the last time I had a glance with a quality hatchet. Handle ergonomics plays a huge part in this as well, and axe handles are optimal for such work. You need a secure grip which fills the hand and allows a solid drive. Though the blade angle does influence it as well. When the edge sweeps up, the natural draw of the chop/cut follow the angle. When the edge sweeps down (khukuri), the edge gets pulled the opposite way from which you are drawing it, and this can cause your grip to be thrown off. Experience is very critical here.


-Cliff

 

[Singularity]

Hi Cliff,

I also like this kind of discussion.

I totally agree that this is only the discussion of one aspect of performance. Edge and blade grind, blade thickness, and edge angle are some others, amongst many more. This is the way I intended it, isolating some of the parameters. So try to consider or imagine knives of the same weight, grind, handles, just the geometry is different.

I do not agree totally in regard to glances, as the geometry is there much relevant. Doing a swing with the wrist works with a golok or a saber, for the reasons I explained, when it is dangerous with a khukh.
(in my experience)

So sure you can correct the problem with quality grips, right edges profiles, or as you said experience, but you are just correcting the problem, as opposed to NOT having the problem when the geometry is right !

Sure you should follow the same angle from start to finish, BUT,
experience works while you are fresh, when tired, you do stupid things (at least I DO !), with less accuracy, and that is where the instinctive blades come back. The experience needed for a saber-curved machete (or golok) is close to zero, when some time is needed to understand how a khukhuri works.
Does that mean that the khukuri or hatchet is more efficient? Of course not, just that it is less instinctive to use.

BTW I have got stitches from both hatchets and khuks in my life, and this tailored my quest for understanding.

I reckon axe handles are optimal for such work, the main difference being that an axe is held with both hands, thus minimising the danger of handle rotation. A proper axe has also it's edge much much further from your body than a big knife or hatchet, so it is less of a direct problem to you.

Now regarding hatchet handles, most nowadays are this Canadian S handle, which strangely enough lowers the hand at or below edge level, while providing control over two axis during the blow, as the hand is angled.

Sure as you explain, a kukhuri blow will try to pull the kukhuri from your hands, and a blow from a golok will try to push it in your hands (pulling while applying the blow is a proper saber movement) but most generaly, it is the material being cut that displaces itself (depend the size...).

BTW since you asked last time in the review, I have unburied my old machete, and will compare the goloks to it. From memory, it was not a performer at all.

I'd love to see a review from you on one of these goloks...

I am much happy to discuss this with you, even if we might have to agree to disagree in the end (unless you make me change my mind or reverse)


Cheers and thanks.

 

[Jimbo]

I don't have much time right now - but a comment on hatchets. I believe that experience has as much to do with lack of glances as anything. You've done a pile of cutting with them, Cliff.
As the saying goes, "there are bold fallers and old fallers - but no-one has ever seen an old bold faller".
My take on things is that you know now when not to chop at a certain angle, and avoid certain situations instinctively.

 

[Cliff Stamp]

Singularity :

Doing a swing with the wrist works with a golok or a saber, for the reasons I explained, when it is dangerous with a khukh.

I would not argue against your comments about blade sweep effecting stability, you present an interesting point which I never considered, and I thank you for bring it to light. To clarify my comments on the other aspects of stability, I agree you can discuss an aspect in detail, however you can't then simply generalise to broad blade categories (goloks vs khukuris). To make an overall judgement you need to consider all aspects. Note for example not even all goloks have the orientation you mention, the Martindale version for example is straight spined.

So sure you can correct the problem with quality grips, right edges profiles, or as you said experience, but you are just correcting the problem, as opposed to NOT having the problem when the geometry is right !

The upwards curve of the blade on goloks sacrifices power, a negative sweep locks more force downwards into the medium. Like all blade aspects, it isn't a matter of right or wrong, but tradeoffs of performance in one area to another. Consider also for example, the penetration ability of the tip on a chop, it is extreme for a khukuri and nonexistent for up swept blades.

There is yet another aspect of chopping ability that we are ignoring which is method. I don't tend to work with the blade tips very much for bucking or felling. I prefer almost right in front of the handle. A lot of the power for chopping with small blades I generate with heavy wrist torque. If I use the tip for the contact point, the leverage disadvantage causes the penetration to falls off.

I reckon axe handles are optimal for such work, the main difference being that an axe is held with both hands

To sidetrack a little, an axe swing is not really two handed in a simple sense. You stabilise with one hand, and guide with the other which moves freely along the handle. The power also does not come from your wrist or arms, it is from your body motion as a whole, which means the end better be comfortable and extremely secure.

Back to the issue at hand, the same handle is also on the pure one handed hatchets. That swing has of course no guiding hand (which is why hatchets are more dangerous than axes generally), and you have to supply the power with your arm as it is far too light for a body drive swing usually. However the bottom of the handle (which is what you hold on to), makes a wonderful heavy knife grip, which you would expect.

I look forward to your machete comments, it would be informative if you could rework the very edge to be similar to the golok. I will be looking at one of the Valient blades in awhile thanks to Jimbo. It is nice to see them getting discussed, as they seem to be solid working blades. If the one that I work with plays out, there are several I will pick up to look at.

I had been thinking recently that the Martindale knives (Golok, Jungle Knife, and Paratrooper), are the best buy performance wise for 10-12" blades for general outdoor use in areas of woody vegetation. However the prices for the Valients are close, and they have full convex grinds. Are there any details yet on the exact hardness and heat treating procedure (are they normalized, how many tempers) . What steel is used? Are they forged from bar stock cut to length, or shaped from a much smaller piece of steel.

Jimbo, yes, I learned chopping on a hatchet which is tradition here, probably not a good one though. My axe experience is in excess of my long blade use, which favours straight bowie orientations, again just tradition.

-Cliff

 

[Singularity]

Hi Cliff,

To clarify my comments on the other aspects of stability, I agree you can discuss an aspect in detail, however you can't then simply generalise to broad blade categories (goloks vs khukuris). To make an overall judgement you need to consider all aspects.

Totally agreed. I gave names as examples, sorry but by control over english language sometimes forces me going to the essential, rather than getting more lost in words, that is why you got a drawing. Surely, Kukhuri, machete, or goloks are just examples, and as you said are very wide categories. The drawing shows what forms I am talking about.

The upwards curve of the blade on goloks sacrifices power, a negative sweep locks more force downwards into the medium. Like all blade aspects, it isn't a matter of right or wrong, but tradeoffs of performance in one area to another.

Again agreed, as you attack the material with an angle, it will come toward you with a khukuri and away with a saber/golok that is the drawback, specially felt on hard but flexible material.

Consider also for example, the penetration ability of the tip on a chop, it is extreme for a khukuri and nonexistent for up swept blades.

Point taken. Ah, I rarely use the tip to penetrate, but when I need to with a swept blade, I use the classical stabing saber movement, tip down, edge up.
Off course also, everything that is not provided by the geometry of the blade, can be with just a bit more difficulties with the geometry of the body... This is whay the geometry is just a parameter. But le'ts discuss this aspect, we will surely come to the other aspects in time.


I'll pass on your comments on axes and hatchets, as I can only agree.

I look forward to your machete comments, it would be informative if you could rework the very edge to be similar to the golok. I will be looking at one of the Valient blades in awhile thanks to Jimbo. It is nice to see them getting discussed, as they seem to be solid working blades. If the one that I work with plays out, there are several I will pick up to look at.

Right, I'll try to reprofile (already did !), but I doubt I'll ever get a so fine working edge with a so shallow angle on a machete...
I'll keep you updated with the few next items (parang, baiwan sword, dams golok...) I should have here before the end of the week. I look forward to read your tests.

I had been thinking recently that the Martindale knives (Golok, Jungle Knife, and Paratrooper), are the best buy performance wise for 10-12" blades for general outdoor use in areas of woody vegetation. However the prices for the Valients are close, and they have full convex grinds. Are there any details yet on the exact hardness and heat treating procedure (are they normalized, how many tempers) . What steel is used? Are they forged from bar stock cut to length, or shaped from a much smaller piece of steel.

The convex grind may give an advantage, we'll see.
The exact hardness is unknown. Jimbo and I cannot agree he places on the low 50 , I place at the upper 50is, though he reckons edge-holding seems better than 50. The blades are diffentially tempered using a clay and coal mixture, and the edge tempering runs for 1 to 1.5 cm on the edge. So we are talking Japaneese like differential tempering! The steel is spring steel, and I'll ask Mr Suwandi about provenance. I think they are forged shaped from smaller pieces of steel Mr Suwandi told me that many craftmen are involved: blacksmith (for the damas) blade smith (shape), hardener (only tempers and harden) handle maker, scabbard maker, etc... The fact the hardener is a specialized person seems a good point to me.


Also there is chopping and chopping:

There is chopping where the blade stops in the material, because of thickness, absorbtion... There you are interested in the ratio of "force applied" vs penetration, and also blade sticking in the material. (not to mention vibrations...)

Then there is chopping/swinging where the blade passes through the material, there you are interested into being able to brake the swing.
(and vibrations ;-)...)

I'd like to see figures for this, but I'd bet that for a given force, the curve is half-parabolic for penetration versus material surface.

Also impact surface is a parameter, chopping 2x4 by the 2 side is not the same than by the 4 side.

Jimbo and Cliff:
Agreed on the shallowness of angles, but I think this is another story which has rather to do with the way the wood fibers are orientated, the way they absorb or deflect the original impact, and what is the most effective way of cutting the most of them with the same amount of energy.
You surely do not hit a tree branch at 90 degrees because the branch deflects under the blow. So you use some 30 to 70 degrees, which place part of the original impact along the fibers themselves in a direction into which compression, extension or deflection is impossible. Hitting at 90 degrees also compresses wood fibers under the edge, thus making it locally harder under the blow.

Try different materials and you'll surely get different results.

OK, yes I have been playing a lot with fiberglass materials, and fibers orientations in the past. (one of my projects is still, one day to make THE fiberglass sheath).

Now what I say is that (one of) the reasons for glances (or handles rotation) on some geometries, is not when you use angle in the blow, but when the blade is at angle with the blow (which might itself of course already be angled). This is what I mean by "angle of attack", it is the angle at which the blade is from the direction it is being driven, not from the material. Am I clear now?

Surely also sone other parameters are of influence, such as blade grind...

Please notice that so far our discussion has been mentioning angles with material in the 3 dimensions.

Cheers,

 

[Jimbo]

In regards to glances, these are caused when you change the angle of the swing. You should follow the same angle from the start to the finish. When you try to come in at a different angle than you intend to enter the wood, it takes a tremendous amount of skill to maintain the same angle in the wood, as it is a very short distance. The other major problem is coming in too shallow . The blade then clears the entire chip out and continues across the surface of the wood. Higher cutting blades are also far less prone to glancing as they penetrate deeper with less effort.

Good points! An old trick for splitting with narrow bevelled falling axe is to deflect the blade slightly just after it hits the wood. the deflection of the axe blade will pry large chunks of wood apart. The point in mentioning this is that the forces are remarkably large.

Along the same lines as the discussion of knife blades is bringing in carving hatchets and axes. A typical hewing hatchet will have a long absolutely straight edge. Most often though the hatchet is used with the blade at somewhere around 45 degrees to the line of the intended cut. This places the hand just at the point of the cut or in front of it. Gransfors have taken this one step further with an upswept curved edge. The Gransfors appears to have higher efficiency, but takes more skill to control the cut. The reason for throwing this in is that the GB carving axe was designed by Willie Sundqvist. I haven't been able to get his book yet and why he designed the axe that way might throw some light on the matter of edge curvature.

One thing is for sure - this is one complex topic once you get into it.
Optimal curvatures of axe edges for chopping rather than carving have varied greatly, and much of the reasoning behind the designs has been lost. Bernie Weisgerbers "An Axe to Grind" - available online - shows the proper angle of an axe head so that if the back of the handle is placed on a table, the axe edge will touch 1/3 of the way from the heel of the blade. I've always heard it as being necessary to have the centre of the axe edge touch. Curvature and shearing come in here too.

I believe singularity has really started something here which will be discussed for a while....

 

[Singularity]

Cliff:
Sure you stated the glance mechanics differently, but we understood each other.

Ok, I've been giving more thinking about it.

The "handle axis" as I described it may not be the relevant axis, (it does not work for hatchet handles. one count imagine a knife with a pushdagger type of handle, chop with it and still experience glances) it may well be more complex:

A chop is a swing created arround 3 main centers of rotation : shoulder, elbow and wrist (pelvis too). Whatever is the point of rotation (or combination) used at the moment of impact, if you draw a line from this point to the center of gravity of the blade, if the edge is lower, you are in a glance-prone chop, if the edge is in-line or over, you'll be cleared.
The whole mechanic is wether the blow obeys to stable equilibrium dynamics (where oscillations bring back to equilibrium), or unstable equilibrium dynamics (where ocsillations bring away from equilibrium).

Jimbo, Sure, curvature would have it's own shearing effect. also a hatchet is mainly designed for the first type of chopping I described, so, it must be working on penetration and sticking.

 

[Cliff Stamp]

Singularity :

I'd bet that for a given force, the curve is half-parabolic for penetration versus material surface.

What exactly do you mean by "material surface"?

Also impact surface is a parameter, chopping 2x4 by the 2 side is not the same than by the 4 side.

Penetration will be inversely proportional to the impact length as pressure is linear with the length of the impact area. There are some complications but they are small effects (for example deeper cuts are smoother by the very nature of taking longer which acts to actually increase the penetration further).

[angle used in the cut/chop]

... which has rather to do with the way the wood fibers are orientated

This is a factor, as is the force distribution. When you chop at an angle, the force is split into one component which drives the blade straight down into the wood, and one which brings it across it. At the same time the grain has to be considered. Chopping at 90 into the wood puts the maximum amount of force into the downward drive, however it is at the worst grain orientation and thus penetration will be low. Chopping at a very low angle puts little force down into the wood, and a lot of force across. At the same time you are cutting very close to through the grain and thus will induce a high splitting action along the grains and thus the blade will glance very easily and at high speeds.

... (one of) the reasons for glances (or handles rotation) on some geometries, is not when you use angle in the blow, but when the blade is at angle with the blow (which might itself of course already be angled).

Yes, for optimal penetration and stability, the force should be applied consistently along the direction of the cut, this is why you should come in at the angle you intend to go through the wood. Variations from this are dangerous as noted for increasing glancing, they are also very hard on the blade as they induce lateral loads which the blade can't resist nearly as well as it can direct compaction.

Jimbo :

Gransfors have taken this one step further with an upswept curved edge.

The same principle is at work in skew chisels. You have an "effective" angle which is COS (skew angle) * actual angle. This is just bringing the power of the draw cut into a push cut. Lee talks about this in his book on sharpening. For example a skew of 45 degrees reduces the angle by 30% .

-Cliff

 

[Singularity]

Hi Cliff,

If you agree, let's suspend this discussion for a while. There has been very good things said, I must reread it and think about it.
Also, and more important,I have got some more real things to play with:

I think you'll understand...

Quick answer however:
Material surface: surface of material that will be cut.