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(WiP) A kukri's "working edges"

Discussion in 'Himalayan Imports' started by killa_concept, Feb 28, 2010.

  1. killa_concept

    killa_concept

    May 19, 2009
    (This is currently a Work in Progress - pictures and additional info will be added)

    Section 1 - Sharpening Method:
    People have different ways of sharpening their khuks, but most HI members who have tried it will tell you that a convex grind (whether by hand or with the aid of a belt sander) is the way to go. Arcs are inherently stronger than straight lines, and this combined with the addition of more metal behind the edge allows a convexed chopper to stand up to heavy impacts much better than simple V-edges. While a convex edge does compromise some slicing capacity for increased durability, a properly convexed edge can still be razor sharp

    I personally convex my kukris by hand using a simple mousepad/sandpaper set up. This method is great for those new to sharpening and without large funds - a mousepad and tacks (or double sided tape) can easily be had for free and an assorted pack of wet/dry sandpaper can be had for ~$5 from a superstore or autobody shop. While it's definitely not necessary, I personally go to 2000 grit paper then finish off with a .3 micron chrom. oxide loaded strop leaving a shaving edge all throughout the khuk. I also tend to increase the angle at the sweet spot to make it more resilient to heavy impact while leaving the rest of the blade more acute. If you've ever read John Lofty Wiseman's "SAS Survival Handbook," he makes the suggestion of thick-spined parangs (fairly khuk-like IMO) as well as deferentially sharpening them to give different "working areas." I found this video where he vaguely explains the logic behind deferential sharpening as well as some other handy safety tips for large choppers. I'm a strong believer in this method for large knives, as it tends to prolong the edge and lengthen the time between sharpening sessions (it's even more apparent with kukris that are deferentially hardened).

    Here's my convex sharpening rig: Strips of wet and dry sandpaper ranging from 120grit up to 2000, part of an old mousepad, some double sided tape, and a self made strop with .3micron chromium oxide powder. The latter part is certainly not necessary - you can get a shaving sharp edge simply going up to 2000grit sandpaper and then stropping on an old leather belt.
    [​IMG]

    And like I said, with a bit of practice, a shaving sharp convex edge is quite doable on a thick kukri. Even after a decent bit of chopping, you only need to pass the khukri over 2000grit and strop to bring it back to this level of sharpness (about 5 minutes of work).
    [​IMG]

    Section 2 - The Different "Working Edges" of a Kukri:
    [​IMG]

    Blue: the tip and although not as "soft" as people seem to make it sound (probably 52ish HRC), its being directly next to the sweet spot makes it prone to very hard impacts if not handled correctly (hence making it seem "soft" through juxtaposition to the sweet spot). I personally don't make much use of this area except during slicing actions (like if you were to gut an animal, slice up some onions - or perhaps slice the packaging tape to a box containing yet another kukri :p). Being the point of the knife, I guess it's also what you'd use for a stabbing action, but I've never found myself needing to use a khuk for such a task.
    Green: The "sweet spot" or hardest area (generally ~58-62 HRC) and the only real area you want to use for heavy chopping. Although I sharpen this section to the same level as the others, I tend to increase the angle of sharpening ever so slightly here, making it less prone to deformation during heavy chopping tasks. Obviously since it's the hardest section, you can use it for pretty much any other task you see fit. Also, being the only section of the blade that naturally makes contact with what you're cutting (when perpendicular), you'll end up using this area extensively - especially if you find yourself using your khuk in the kitchen :).
    Yellow: Belly of the blade and probably 55-57s HRC towards the sweet spot and gradually lessening down to low 50s HRC at the recurve. I use this area for lighter vegetation - from grass up to smaller branches. Since I sharpen this area more acutely than the sweet spot and since it doesn't suffer deformation from hard impacts (impacts that should exclusively be handled by the sweet spot ;)), it has an easier time slicing through springier objects instead of pushing it away like the sweet spot will tend to do. The overlap into the green area in my diagram just means that I inevitably use that area for these tasks as well (when swiping at a patch of grass for example) but for reasons already stated, the full yellow area is more suited.
    Red: The recurved area and relatively soft (probably 50-52 HRC). My #1 use for this area is draw cutting (by gripping the handle of the knife with one hand and the spine towards the tip with the other). Since it's curved and sharpened acutely, it does a great job at stripping bark or shaving wood when used like a draw knife. Again, since it's somewhat softer in this section, assess how hard the bark/wood is before using this section in this manner. I also occasionally grip the kukri by putting my pointer around the cho and my thumb on the spine to use this area as I would a regular knife. Lastly, reverse this grip (thumb on/near cho, fingers on spine) and you're in a great position for peeling fruit (if you have a lighter kukri and/or your wrist and forearm can take it :D)

    Section 3 - Kukri Grips and Techniques

    Pending
    (definitely need a picture tutorial of the "wrist flick" technique to add extra momentum while chopping)
    (could also use some member submitted pictures for this ;))


    Section 4 - Minor Edge Maintenance

    I can't stress proper technique enough: not only for safety reasons, but also for the sake of your kukri. With proper usage of the "working edges", you probably won't have to deal with rolling/deformation and the laborious resharpening that goes with it - the kind you would have to deal with if you used improper technique (or, heaven forbid, tired yourself out and got sloppy) and ended up smacking a fairly well-seasoned tree with the tip or belly of the khukri. I've done it to my 18" Vojpure and getting the dent out without aid of a belt sander took a good, long hour with 220grit sandpaper and a mousepad :eek:

    Normal use will still of course wear down the edge and if you're like me and love to keep your knives razor sharp, you'll want to perform minor edge maintenance after any heavy usage. Generally it only takes about 5 minutes and keeps your kukri's edge in pristine condition. It pretty much just consists of 3 simple steps: using the chakma to straighten out the edge, a quick sharpening job using mousepad/sandpaper method with only 1000grit sandpaper, and finally stropping (a simple leather belt will do if you don't have a dedicated strop handy). That's all there is to it :thumbup:

    (pictures + more pending?)
     
    Last edited: Jul 4, 2010
  2. killa_concept

    killa_concept

    May 19, 2009
    I realized we didn't really have a good Info thread as to the usage of a kukri, so I took some stuff from old posts of mine and am assembling this together for the sticky thread. It's a work in progress and I would love to see my fellow members share ideas and add to it: techniques, usage, and if at all possible, pictures as well.

    The ultimate goal of this thread is to show that, while the kukri makes for a great chopper, it's also a very versatile design and capable of taking on a large array of chores. Please keep that in mind as you add to the thread ;)
     
  3. zhangmaster12

    zhangmaster12

    504
    Sep 14, 2007
    wow. Great post man! The sweet spot is quite a but smaller than I expected. I cant wait for the usage section.
     
  4. Ugly Duck

    Ugly Duck

    568
    Oct 6, 2008
    I also use the mouse pad & 2000 grit & finish on a strop loaded with 0.5 micron grit. The sweet spot just kinda naturally gets an increased angle because its so dang hard that less metal is removed in that area with each stroke. Wutta great design....

    P.S. Great post!
     
  5. killa_concept

    killa_concept

    May 19, 2009
    It varies depending on the kami, the model, and even the pieces of the same model made by the same kami - each kukri is individually hand crafted after all and will have it's own unique properties. My diagram was sort of generalized to account for variations. As they say, your mileage may vary... If you absolutely have to know and don't mind scratching up your edge, you can always use the file method to find what section is approx what hardness (a 55 HRC file is probably the best to use, as a 60+ might leave scratches that are difficult to get out)...

    As a general rule of thumb though, the "curved" section just prior to the tip and a little bit of the belly is going to be the very well-hardened section or "sweet spot". It's also the area that will naturally strike first unless you're sloppy ;)

    Yep - the kukri seems to strike most people as an odd design with many unnecessary traditional aspects... but after using one for a bit, you come to think that those traditional/decorative features are still implemented to this day because they also serve a function. The rings for example, help me facilitate a "wrist-flick" technique... and the cho is great for choking up on to do finer work. Very great design.

    As for the angles, I just use very minimal pressure when I convex my khuks and try to aim for a ~18 degree angle all throughout (the "give" of the sandpaper naturally brings the final edge to ~20ish degrees which is perfect IMO). I then go over the sweet spot with an increased angle of ~20-21 degrees to make it a bit more stout.
     
    Last edited: Feb 28, 2010
  6. MrMike

    MrMike

    147
    Jan 22, 2006
    From my experiences with 1500-grit sandpaper, the sweet spot is very hard to sharpen to a keen edge. It is very apparent after sharpening the length of the blade where this harder steel is. On my 18" Bura Sirupati, I would estimate it to be 62rc, and roughly 3/4" in length where Killa's diagram indicates.

    I had to rough shape the sweet spot with a fine diamond paddle and then work it with sandpaper on a rubber eraser. After all of this, it's still not what I would consider sharp. Every other part of the blade is very sharp. I have a CAK made by Sher in which the steel is softer, therefore much easier to sharpen.

    The benefit of this I guess, is that the sweet spot can take much heavier impacts without rolling.
     
  7. Nicholas

    Nicholas

    896
    Apr 1, 2009
    Thanks for this highly-detailed post, k_c; this is exactly the information that I was gunning for when I first came to the group, and will help out enormously from now on.:thumbup:
     
  8. Wolf_1989

    Wolf_1989

    Mar 30, 2007
    The sweet spot on practically all of my H.I.'s is a bit longer; about halfway into the yellow portion in the picture. The exception being the Super CAK by Sgt Khadka which seems to be fully hardened a half inch from the tip all the way down to just before the inner curve of the blade.
     
  9. killa_concept

    killa_concept

    May 19, 2009
    Well the "sweet spot" of the kukri isn't just about the hardness - it's also based on the natural point of impact and largely on the center of percussion. Even if the belly is well hardened, it won't bite nearly as well as the "sweet spot" illustrated in the diagram. Have you personally tested your kukri with a file?If so, what hardness was the file, how toothy was it, and was it relatively new/unclogged? I have generic, cheap chinese file that I picked up at a hardware store and it seems to be about ~55HRC. Using this on my Vojpure by Sher, I would agree that the hardened section does extend further past the area I illustrated. But when I use my Nicholson file which is rather toothy and about 65HRC, it shows the sweet spot to be where it is in the diagram (but again - this doesn't translate to the sweet spot). I guess I sort of understated the hardness of the belly... it's probably 55ish towards the sweet spot and 45ish towards the recurve

    That said, thank you - I edited my post to be more accurate as to the rockwell hardness of the different sections :)
     
    Last edited: Feb 28, 2010
  10. ivan51

    ivan51

    Dec 9, 2003
    great post man:thumbup:
     
  11. Karda

    Karda Banned BANNED

    Jun 1, 2007
    Looking good Killa! I can't wait to see the final product.
    Don't Kill yourself though :D theres plenty of time to do it up right.
     
  12. wave

    wave

    8
    Jan 9, 2010
    Very good concept!!!:D
     
  13. killa_concept

    killa_concept

    May 19, 2009
    Posted up my sharpening rig and the results of a properly convexed edge. I might make a small picture tutorial as to the wrist-flick that should accompany a khukri chop for added momentum, but it seems pointless without being able to show the difference in depth of penetration on a tree limb. Maybe a fellow member can take care of this for me

    I might also post up pictures to explain the different grips I mentioned in the "working edges" section later ;)
     
  14. warty

    warty

    Mar 2, 2010
    Well, I like it so far and once I actually have an HI khuk, maybe I can do some chopping for you....
     
  15. Nicholas

    Nicholas

    896
    Apr 1, 2009
    Not to be a spoil-sport, but I should point out that, despite having made great progress with my own Convexer, and having access to 2000-grit sandpaper, I haven't been able to get ANY part of it up to shaving yet. I can get the recurve to cut paper smoothly, almost as well as my Rusty SD, but no shaving yet!
     
  16. killa_concept

    killa_concept

    May 19, 2009
    Hrrmmm - I ended up running into the same issue the first time I convexed a kukri, but since then I've been able to get them all shaving sharp. This problem tends to happen when I use too much pressure or too high an angle while sharpening - the final edge angle still cuts just fine, but it's simply too obtuse and with too much metal behind the edge to shave. Try laying a crummy old leather belt down flat on something and pushing the blade along it edge first. Start with the side of the knife flat against the belt then begin raising the angle as you go. It will eventually "bite" into the belt at a certain angle, and that will show you what the final edge angle is on your kukri. If it's more than 25-27ish degrees when it bites, you've probably been sharpening it at too high an angle. You want about a 40-42ish final angle on a kukri (20-22ish on each side) - the kukri is hardened well enough to not deform at this angle and will be sharp enough to shave and cut very well.

    Let me know how it works out Nic ;)
     
  17. dondulah

    dondulah

    61
    Dec 24, 2009
    I was waiting for you to upload that pic because I was having trouble picturing it in my mind. That helps me so much! Thanks for sharing.
     
  18. Nicholas

    Nicholas

    896
    Apr 1, 2009
    What I've long been doing is, to go at a very shallow angle, as if I were trying to shave the grit off the sandpaper. If anything, some experimenting today showed me that I might have it TOO shallow! But, I'll keep experimenting......
     
  19. killa_concept

    killa_concept

    May 19, 2009
    Wait - if the motion you're using is trying to shave the grit off the sandpaper, does that mean you're pushing the blade into it? :confused: Convexing is supposed to be done with a stropping motion i.e. leading with the spine
     
  20. Nicholas

    Nicholas

    896
    Apr 1, 2009
    No, I'm leading with the spine. That's just describing the angle.

    What I was worried was, that the angle STILL seems to be influenced by the steep microbevel that those people put on it, which it is too easy to simly polish to a high lustre. (The recurve, where it cuts best, is simply where I've done the best job of removing it.) But after checking my other HI knives (including he Bura Salyan, with was never "professionally" sharpened), I've realized that this is a red herring. "Shaving" sharp isn't a realistic goal; I'm just going to try to do a better job cutting paper.
     
    Last edited: Mar 9, 2010

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