SN1 question in regards to splitting wood

C

Cliff Stamp

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I am currently reviewing two SN1's from khukuri house, one of the problems is that the shock is excessive if you try to baton these through wood. This can be effected by many factors such as the overall shape of the blade (usually the main criteria) but to a lesser extent the nature of the steel. Anyone with a HI SN1 who has a few minutes to spare, could you baton it through a few pieces of wood of decent size (take at least a half dozen shoulder wings to split) and compare the shock to a fairly straight blade, bowie or machete pattern. Thanks.

-Cliff
 
SN1 = Service No. 1

I have played with a few. They are somewhere between a 15" BAS and a 15" Sirupati in H.I. terms. Usually the handles are smaller/shorter and the blade lighter....no SofS...rough finish....thin scabbard leather.

Curious about your test, Cliff. Keep us posted.

I think a more fair test would be to find someone who had some of the Shop 1 models - they were closer, I think.
 
Sorry, I know that there are those out there who dearly love their BAS's. I've tried the 15" BAS, and even the oversized 16" Big BAS. 14" and smaller I like. 16.5" and up I like. The BAS - well, it's like kissing Great-Aunt Maude. Just my own humble opinion. Not that anyone asked.
 
pendentive said:
SN1 = Service No. 1
I think a more fair test would be to find someone who had some of the Shop 1 models - they were closer, I think.
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The Shop 1 models -were- made by the Khukuri House or Shop 1 as it was called way back when. Their quality may have slipped now and then but the HI Modles were and are excellent!!!! My Barbie's khukuri is a 15" Shop 1 AK with the scrolled butt cap. Those were the good old days in many ways. No flat or hollow ground edges and no so-called habaki bolsters!!!!
Everyone back then was wanting to learn how to sharpen the dreaded Convex Edge!!!! Some things never change.:rolleyes: ;) :rolleyes: :D
 
Yvsa said:
Everyone back then was wanting to learn how to sharpen the dreaded Convex Edge!!!! Some things never change.:rolleyes: ;) :rolleyes: :D
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hehehe....I *used* to need to learn that! :D
 
Unfortunately, no.

I mean the one you always tried to stay away from 'cause she embarrassed the heck out of you by telling stories about you that you'd rather die than hear again. And others you couldn't refute 'cause you had no memory of.

Added to the agony of ignoring any dignity you might have left, when you and your cousins got together your mom and her sisters would start talking in Hungarian, stop and look at you, and start ROTFLMAO.

One time my mom's two eldest sisters were on a bus and they started commenting on a poor guy's big schnoz. In hungarian. They went on and on about it until the guy's stop, when he told them in perfect Hunky that " that's not the only big thing I have."
 
Nice... :barf:

Thanks for clarifying. I have those sorts of relatives, but they're not so good with the switching to the mother tongue when they have to be coarse. Makes me wish I could knock myself unconscious at will.
 
Cliff Stamp said:
I am currently reviewing two SN1's from khukuri house, one of the problems is that the shock is excessive if you try to baton these through wood. This can be effected by many factors such as the overall shape of the blade (usually the main criteria) but to a lesser extent the nature of the steel. Anyone with a HI SN1 who has a few minutes to spare, could you baton it through a few pieces of wood of decent size (take at least a half dozen shoulder wings to split) and compare the shock to a fairly straight blade, bowie or machete pattern. Thanks.

-Cliff
Click to expand...

Cliff,

I will relate a very brief summary of what I think I now know from, in large, my experience of using a fairly large and massive kukuri to split wood with a baton. The Knife was an HI Ganga Ram, weighing 3 lbs with a length of 21" overall.

If you search the archives, you can find my posts from that time. The knife suffered from some hardening issues, but the salient point is that the tang broke at a stress riser right at the buttcap!.

With a knife this long and heavy, the sword issues of point of percussion, etc. probably begin to make a very significant appearance. Prior to the failure, I noticed the issues of shock that you mention when using a baton.

After some discussion, and practical experience, I conclude that when using a baton on a large knife, the edge contact with the wood to be split must be at or near the center of percussion, as must the blowtko the spine of the baton. If this is not the case, extreme shock and stress occurs, indeed shock that is greater than would be tolerated if the hand is actually strongly grasping the knife and making a strike that misses the sweet spot.

When the center of percusssion is coincident with the portion of the edge in contact with the target and the baton strikes the spine in a corresponding position, the shock at the hilt is minimal. The energy is effectively transmitted to the target. If the above conditions do not apply, some of the energy is manifested as shock at the grip and intermal stresses that must be dissipated by the knife itself.

My suspicion regarding your comment about the "overall shape of the blade" being the culprit is simply that the actual center of percussion is either not where you expect to find it, or not in the area that comes most natually to your method--either the portion of the edge in contact with the wood, or the poriton of the spine struck is far from the "sweet spot".

If a large blade (or for that matter, anything like a baseball bat) suffers a severe impact that is not in the sweet spot, the blade (or bat) will dissipate the energy itself possibly with internal damage, as opposed to transfering it.

In my limited experience big knives behave differently than small knives in this respect. In big heavy knives, the phenomenon is more pronounced.

Perhaps some sword-people could add to this.

I have found that proper attention to these issues totally minimizes shock when using a baton with a khukuri, and that neglect of this produces surprisingly intense shock at the grip with the possibility of damage to the kinife, which will most likely occur in the tang area.

I have no experience with large knives of other shapes in this regard.
 
Yvsa, thanks for the details about Khukuri house, the quality is definately off on these ones, you can actually visibly bend them by hitting them with a piece of wood, which should not be that hard to resist with a 3/8" thick blade. They also show pressure flakes like glass knapping when they chip out which I have not seen before.

Firkin you are right on, it was a simple matter of center of percussion. Last night in a few minutes I found it was possible to split wood without getting huge shocks, however you had to basically split the wood with the part of the blade right in front of the handle, this is more than a little awkward as you are using a recurve, and hitting the front part of the blade which is now at a downward angle.

-Cliff
 
Cliff Stamp said:
Firkin you are right on, it was a simple matter of center of percussion. Last night in a few minutes I found it was possible to split wood without getting huge shocks, however you had to basically split the wood with the part of the blade right in front of the handle, this is more than a little awkward as you are using a recurve, and hitting the front part of the blade which is now at a downward angle.

-Cliff
Click to expand...

Actually, I don't think that it's quite that simple when batoning is involved. As I understand it, when holding the blade and making an impact at the COP, the vibrations are such that a node occurs at the grip and the impact point. With waves, essentially what this looks like, there are higher harmonics, and it sounds to me that is what you have found if you are not striking the spine opposite to the edge contact. Another crude way of thinking about it is that you are effetively clamping the edge, then exciting vibrations. If the clamp is not at the node of the fundamental ("sweet spot") then a different vibration pattern is forced onto the blade with different node locations which is why you are not striking the same part which is doing the splitting. This solution may or may not be less awkward than utilizing the "natural" COP.

I agree that the bent shape of the blade can make things get awkward especially if over the course of several baton blows, the blade tilts a lot while embedded in the wood. With the khuks that I've used for this, things worked best when the sweet spot (which was properly located in the belly) was in contact with the wood, and the baton blow impacted the spine directly above it. The spine was close to horizontal, which meant that the handle was angled down. If the wood you're splitting is too big to allow for this, all bets are off, one of the higher harmonic solutions may work, but I think you really need a longer khukuri (or an axe).

This does bring up an interesting question though--does anyone have a khukuri where the COP is in the wrong place?
 
Yes, it does work most smoothly when you impact over the COP, however that only works until the khukuri is driven its width into the wood. With the wood still not split you then either have to hit forward, or rear. Going towards the handle is problematic for many reasons, so you end up going out along the tip which is now inducing many powerful vibrations. SO much so I mean I lost the ability to hold onto the handle after trying to see if I could tough it out. So you start off with it in a less than perfect spot to allowed continued functional performance.

Yes I was using phrasing loosely in the above, with the COP refernce, I don't think you can simply make a 1:1 connection for reasons you noted. I should actually compare where it is and the optimal batoning spot which is going to depend on the nature of the wood I would suppose. Knot placement may be a factor here because the khukuri will treat this as the highest fixed point as it will naturally rotate around these readily.

Speaking of COP khukuris, I have not used any but Mike Swaim talked about such issues on rec.knives years ago (96 maybe). Not as much as it was in the wrong spot, but just that the deviations from it produced much larger vibrations than on a machete, thus you had in effect a much larger working area and a more functional blade. This was in regards to a few Cold Steel khukuris.

-Cliff
 
Yes, it does work most smoothly when you impact over the COP, however that only works until the khukuri is driven its width into the wood. With the wood still not split you then either have to hit forward, or rear. Going towards the handle is problematic for many reasons, so you end up going out along the tip which is now inducing many powerful vibrations. SO much so I mean I lost the ability to hold onto the handle after trying to see if I could tough it out. So you start off with it in a less than perfect spot to allowed continued functional performance.

Yes I was using phrasing loosely in the above, with the COP refernce, I don't think you can simply make a 1:1 connection for reasons you noted. I should actually compare where it is and the optimal batoning spot which is going to depend on the nature of the wood I would suppose. Knot placement may be a factor here because the khukuri will treat this as the highest fixed point as it will naturally rotate around these readily.

Speaking of COP khukuris, I have not used any but Mike Swaim talked about such issues on rec.knives years ago (96 maybe). Not as much as it was in the wrong spot, but just that the deviations from it produced much larger vibrations than on a machete, thus you had in effect a much larger working area and a more functional blade. This was in regards to a few Cold Steel khukuris.

-Cliff
 
Cliff Stamp said:
Yes, it does work most smoothly when you impact over the COP, however that only works until the khukuri is driven its width into the wood. With the wood still not split you then either have to hit forward, or rear. Going towards the handle is problematic for many reasons, so you end up going out along the tip which is now inducing many powerful vibrations. SO much so I mean I lost the ability to hold onto the handle after trying to see if I could tough it out. So you start off with it in a less than perfect spot to allowed continued functional performance.

-Cliff
Click to expand...

OK, I have experienced this also, the magnitude of the vibrations can be very surprising.

In this case, it seems to me that there are two options:

1) Admit that every tool has a limit, and use a better suited tool as available. If hard enough wood is available, one or more wooden wedges can be fabricated and pounded/batoned into the crack started by the knife. Not as fun, but it can work quite well. Many times the wood weakens in a short time, so one can let the stubborn piece sit with wedges a few minutes while using the knife on another piece, then go back to the wedged piece and finish the job with a couple of further wacks on the improvised wedges. There is also some stuff that would be a chore to split with a real maul and wedge.

2) Find the "new" COP of the clamped blade as you have done, that minimizes the vibrations. This can mean prying the blade out and repositioning it, which is a PITA.

Very powerful vibrations like you describe will eventually damage the some part of the knife, since there is almost certain to be a potential stress risor somewhere in or near the tang (especially since the tang is usually not carefully ground or polished).--At the least, some furniature will loosen or the grip will loosen. The makers of the blade most likely find it inconceivable that the tool would be used in a fashion that creates vibrations so great that it is impossible to hold the handle. I don't think that they can be faulted for that.

My rule of thumb is if I wouldn't like that degree of vibration when swinging the knife, then there is probably a better way to use it.

As far as khukuris being less forgiving if the sweet spot in mis-struck, I don't know if something like that would more attributable to the bent khukuri shape or the weight distribution, which is different than most straight blades that I can think of (maybe a VERY deep bellied straight knife would act the same?). It could just be that the ergonomics of the khurkuri shape allow generation of greater force with less effort (when swinging , not batoning), so that a mis-strike produces stronger vibrations.
 
There are better ways to split it, but this is mainly on small woods, 2-4" thick which are not that difficult to baton through with a straight blade.

I have not doing it [batoning] with my larger khukuris, which I definately have to check, mainly because they tend to be able to split the wood under their own weight, but will have a look at this hopefully with some free time in the next few days.

In any case, this does give some advantage to straight blades inbatoning, of course there are lots of other spects fo woodworking where a khukuri has the advantage.

-Cliff
 
I spent some time the weekend chopping with the khukuris on the hardest wood I could find and noticed no real heavy vibration regardless of the impact areas throughout the main body of the blade. I also reversed the khukuri and used it as a club, it doesn't do this well as the angle is the wrong way but again no real vibration.

I also checked the COP, determining it to within +/- 0.5 cm, and found that when batoning, this was the area I needed to strike to get smooth splitting. What was interesting was that if I deviated from this the vibration was many times more than when using this as a club or chopping.

I investigated Firkins idea that maybe it was the introduction of a new vibration point at the binding point in the wood, however this didn't make much of an effect. I could place knots at various points and hold the blade at different points and as long as the COP was near the contact point all was well.

I think the main effect that is being seen is that the impact time is huge for batoning because the penetration is horrible on seasoned and knotty wood. The blade can sink in may a mm or two, compared to ten times as much even on hard wood on a chop. As the time of collision is directly correlated to the depth, and the impulse delived to the hand directly inversely related to the time, when trying to baton through difficult wood any energy transfer to the hand will be amplified many times over compared to chopping.

-Cliff
 
Interesting stuff Cliff.

What makes the most sense to me, keeping things simple, is that impacts at a node of the natural resonance, or COP, will not excite vibrations in the blade. This must provide more efficient energy transfer, regardless of whether the target splits easily or not. Likewise for the baton. Minimize vibrations in the baton, and knife, and the most energy goes into the target.


I'll have to think more about your idea of the impact time, and the still suprising to me anyway, creation of such huge vibrations when mis-strikes are made when batoning. [at first blush, seems like hitting a knot looks more like an inelastic collision, which would cause the knife to bounce up sharply--but a simple displacement if the COP is involved, which would be felt as a jolt, not a vibration]

There must surely be some similar effect in other large knives, even if not as pronounced?
 
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