Thick spine

JayGoliath

JayGoliath

Joined
Mar 27, 2010
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I would like to ask, is a thicker spine any better than thinner one?

Cotherion's Bonecutter (0.9cm, 12inch ) is much thinner than my ASTK (1.3cm, 18inch) and both used in chopping, it outchops Amar Singh Thapa. :eek:

We could go into bevel, geometry of curve and the weight but let's keep all those at bay.

Do we need thicker spine for chopping?
 
I don't think a thick spine in itself adds anything to chopping, ESPECIALLY if we're not considering weight.

With weight as a consideration: A thick spine will help with adding weight to a blade, so there will be more energy in each chop.

With bevel and blade geometry as considerations: Overall weight of a knife isn't as important as where that weight is on the knife. A knife with more weight forward will chop better than a heavier knife whose weight is distributed more toward the handle. The bonecutter is definitely more nose-heavy than an ASTK, which i feel is pretty neutral. And the bonecutter, being thinner, probably has a more acute angle, which helps it bite deeper than a thicker ASTK.

I myself prefer thick spines though. Dunno why, they just feel more solid to me. Nothing like having a huge chunk of steel in your hand! ;)
 
Jay how a well a knife does what it does if one big regression equation but the short version is (chopping ability= weight+edge geometry+distribution of weight+ergonomics)were spine thickness is part of both all of those.
As much as I like to think or say otherwise I don't really believe that my M43 with its .5" spine can out chop my full sized axe with its over 1" spine.
A thick spine usually implies more weight which adds to better chopping power. But to get "more" weight you can also have a thinner spine with a wider belly. This was the whole discussion here http://www.bladeforums.com/forums/showthread.php?t=762613&highlight=bonecutter over the old style versus "new" style on the Bonecutter. This is just a different way of saying what moogoogaidan just said.
Thicker spine also implies a more obtuse(thicker) edge which is less likely to deform or chip when you hit something hard. A thicker spine and edge will also be less likely to "bind" or get stuck after the hit where wide thinner blade of the same mass might get seriously wedged(stuck) in there.
I like thicker spines on a Khukuri. I can also go to the other extreme and grab a 1/8" thick 24" long machete (which I actually like better for light underbrush & 1" thick limbs) but if I'm going into the woods and can only pack one or the other the .5" spine on my M43 is going with me;)
 
It's pretty much been said: the thicker spine contributes by adding weight behind the edge. The edge geometry is far more important. Given exactly the same edge geometry, same length and curve to the blade, and exact same technique, the thicker spined, heavier kukri will chop deeper.

So it's just one of many factors.
 
Since we are on chopping & technique, I seam to get better "hits" when I land more towards the re-curve than the bottom of the belly(which is where my understanding the "sweet spot is"). Am I just "thinking" I'm getting better hits because it looks that way or is the inside towards the re-curve where the sweet spot really is? I notice the same thing whether its the 12" CAK or the 19" M43.
Thanks,
Ray
 
More info about the "sweet spot" here:

http://www.bladeforums.com/forums/showthread.php?t=720287

...and other khuk working areas

I think, depending on the way you handle the khuk, the "hit" area of the blade changes.
If you grab it by the handle (as an "normal" westener) then you will naturally want to hit closer to the recurve. don't know why but that's what happens

If you keep the handle for the "end" (butt) then one tends to hit the "sweet spot" more accurately. (i.e. 2"-5" back from the tip)

All of this probably have to do with blade weight distribution too.


As for the thicker vs thinner spine:
The Guys already explained it well enough:
Thin blade spine + weight (aka machette) = more chance of the blade getting seriously stuck in the wood. Advantage = better and cleaner tomato cutting
Thick blade spine (already having weight) = more material get's pushed aside during tomato cutting. Advantage more axe like chopping ( i.e. less sticky vedging)
Very thick spine (aka axe) = not good for tomato slicing and considerably heavy. Advantage = great chopper design

The khuks with 3/8 spines are probably the best all round design.
A thinner blade like the Tamang - less chop , more cut-slice
A thicker blade like 1/2" spine - more chop, less cut-slice
Hope this is accurate
 
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oldschool45 said:
Since we are on chopping & technique, I seam to get better "hits" when I land more towards the re-curve than the bottom of the belly(which is where my understanding the "sweet spot is"). Am I just "thinking" I'm getting better hits because it looks that way or is the inside towards the re-curve where the sweet spot really is? I notice the same thing whether its the 12" CAK or the 19" M43.
Thanks,
Ray
Click to expand...

Heck, I'll re-post the pic:
scan0001-1.jpg


What are you cutting?

Referencing the link above, the green area is the sweet spot, the yellow is softer. What I find is, the softer the material, I'm better off making impact closer to where the green and yellow meet. The harder the material, the closer to the center of the green I need to be.

I think the physics of it are like this:
The kukri is a continuous curve, no straight sections. This means that no matter how you hit, you are going to "run" the blade -- i.e. make a slicing action -- as the arc of your swing draws the curved edge over and through the object being sliced. So, when cutting fibrous objects like stalky plants, wood or meat, the cutting enhances the effect. On very hard woods, it isn't easy to slice the fibers, so going for a direct chop at the deepest part of the sweet spot gives better effect.

This is why kukri both slice and chop well. I notice that when I chop straight in on light grass and light stalky plants, they get cut, but mostly just move out of the way. When I strike further back toward the recurve, or even nearer the tip, the blade runs and I get a clean, effortless slice.
 
wildmike, judging by the chart in the link Dan posted I'm actually hitting the the "transition area" but I think I just nailed down a 20" AK so it might have to do with blade drop too.
Dan thanks for the reminder on the links.
I am about done re-handlng my 12" CAK to make it prettier and to make it easier to hold in the traditional v. western grip I made it with a relatively big round pommel to that end. Watch for a very picture intense WIP of a re-handle this week. Also if I get that 20" AK Yangdu made me a beast of a sheath making WIP, gonna need a whole shoulder, of leather, for that puppy and about a mile of stitching:D
Just got the email the 20" AK and the sheath WIP is a go:thumbup:
 
Can't wait for the review:D

I've made some x50:eek: magnification pics of my DC blade!
Will try to post tomorow in the Sharpening Help... tread;)
 
oldschool45 said:
wildmike, judging by the chart in the link Dan posted I'm actually hitting the the "transition area" but I think I just nailed down a 20" AK so it might have to do with blade drop too.
Dan thanks for the reminder on the links.
Click to expand...

The green area was the range of sweetspots that I found, not necessarily that a sweet spot should cover that entire section (i.e. the sweet spot could be 1/2 of the green area in either direction or something). The picture above, which is from my Info thread, is mostly a generalization based on a couple tests I did on the few kukris I had. As kukris are all individually handmade by different kamis and with different designs, it's impossible to say that it applies to every single one. The "sweet spot" also doesn't just refer to the hardened area, but the natural center of percussion as well. Sometimes the two aren't perfectly aligned, but they practically always overlap. Amazing that the kamis manage such a feat just through personal experience and passed down knowledge!

Seeing as though your m43 is my old one, I can tell you that you are quite correct and the sweet spot is a bit further back: if I recall correctly, the hardened zone on that m43 is about 2/3rds of the green area that is closest the yellow. I think that the pointer, more curved design of the m43 (when compared to other kukris with blunter noses like the AK) also puts the center of percussion a bit further back than most and Young Sher properly compensated by also hardening it a bit further back.

That all said, it's better to figure out the "sweet spot" by getting some usage out of your blade than having someone tell you where it is - if the section you're hitting with is biting the deepest, then you're probably doing it right ;) If you're really curious though, just snag a file and run it across the blade to find the hardened area :)

Glad to hear you're getting use out of that m43 (I miss it a tad :() and am looking forward to your project threads!
 
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Killa I already posted the fix for your 43 here http://www.bladeforums.com/forums/showthread.php?t=765157
Part of the battle I'm fighting finding the sweet spot is I'm trying to use it on lighter stuff where I really should be pulling out the machete so that is screwing with my technique development. I'm getting noticeably better with the M43 but the demise of the wood pile has stopped till Wednesday (maybe tomorrow) when the 20 AK shows up:D
The re-handle WIP is 90% done I'm taking 2 vacation days this week to spend time with the wife, render another wood pile into kindling and post that re-handle thread.
The sheath thread could take several forms I may do the 12" CAK first to lear something about the geometry needed and still be a bit frugal on the amount of leather used. When I do the 20"AK sheath that will provide a lot of real estate for ornamental leather carving and I intend to make use of it as soon as I can come up with a design. I will probably incorporate "UB@(peace sign)" into the design of all of them.
 
This weekend, while camping, I found another use for a thick spine. As a meat tenderizer. I pounded more steaks than wood. It's an 18.5" WWII, 28oz, 7/16" thick at the spine. It's also a pretty good chopper. YMMV

Frank
 
A lot of things go into making a chopper, but much of it is subjective. A heavy hitter can be good if one wants to chop down a large tree or cut up a large deadfall. That calls for a blade which can remove large chunks of wood with each bite. This is where you find a use for the big AKs and similar style blades, khuks which have a lot of mass and need to bite deep with each blow.

On the other end of the scale (IMO) is the medium to light chopping, which calls for a quicker, thinner blade. When moving around our property I often have the need to trim back branches which have overgrown trails. If the branch is green then I use a lighter blade like a Pen knife or a GRS (15-16") to cut the branch off with one swing. If the branch is dead I'll often use pruning shears, but that's pretty boring.

I don't want a heavy, thick blade when cutting back branches because there is simply too much mass in the blade to get it moving as fast as it needs to, to cut through the unsupported branch, and to get it stopped before it takes out a knee or goes flying off into the underbrush.

But for serious chopping, mass (weight) can be very helpful.

Andy
 
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