Edge Profile of my 18" Ang Khola

C

Cliff Stamp

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In case you were interested this is the edge profile of my 18" Ang Khola, which I assume is typical :

http://www.physics.mun.ca/~sstamp/images/ak_18_edge.gif

It is often assumed that the high level of durability on the HI khukuris is due to a really thick and obtuse edge, probably because the spine is really thick. However as shown above the edge is actually very acute, compare those angles to a normal production folder.

For reference this is the edge profile of a Wildlife Hatchet from Gransfors Bruks :

http://www.physics.mun.ca/~sstamp/images/gb_hatchet_edge.gif

I am pretty sure I increased the final bit of edge curvature on the hatchet when I sharpened it earlier this year, by about 1-3 degrees. In any case, note that the profile of the Ang Khola is over all significantly thinner.

Note, the edges on both are of course smooth convex curves, the reason why the above are not smooth and flowing is just due to the random error in the measurements.

-Cliff
 
Cliff,

Very interesting, I am impressed. How did you manage to measure the edge angle? Perhaps we can finally get away from the "scary" and "shaving" sharp language and start talking instead about real edge angles.

n2s
 
The profile was determined with a Vernier caliper which can measure to 0.001", although it is next to impossible to read that well when taking edge measurements due to effects like parallax errors unless you are reading above a mirror which in retrospect I should have been.

I just marked a series of lines up the edge profile and measured the edge thickness and width at those points. There are better ways to do it, I just wanted to see how difficult it was with a caliper, not overly actually. I have mapped out the complete cross section, including primary profile of some of my knives.

There is some performance info on the above two blades in the following thread :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=179702

-Cliff
 
Cliff,

Thanks for the info. For a moment I though you may have found a reasonably priced laser to measure the blade. Something like a close up range finder.

n2s
 
The edge was sharpened quite some time ago and a secondary flat bevel was introduced, <0.5 mm wide, simply because I didn't know how to freehand convex curves then. When I cleaned the blade up recently before the chopping comparion between it and the hatchet I restored the profile to a smooth convex curve. It is now very close to the NIB profile. Of course there will be differences from one Ang Khola to another depending on who made them.

As for removing the flat bevel for those curious, the easiest way to do this is with a slack belt sander and just run it along the primary convex bevel and bring it down until it removes the flat secondary bevel. With a sharp fresh belt (even a cheap AO one), this is only a matter of a few minutes, take your time and cool the blade after each pass. I just did this on a 5160 custom that had a secondary edge that was too obtuse for my preferences.

Doing it by hand I take a large (5 lbs) SiC x-coarse waterstone (~220 grit) and hit the intersections of the two bevels and smooth it out. Then I take a series of small waterstones that are only 3/4" wide and smooth out the bevel producing a flowing curve. I finish with a 4000 simply because I have not found a small 8000, and then polish with CrO on leather. Make sure you work the full length of the curvature. This takes much longer that the belt sander obvously, but you can get it done in under an hour easily.


-Cliff
 
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