A Convexed Edge for Christmas

N

Nicholas

Joined
Apr 1, 2009
Messages
896
Long, long ago, on a thread that I have not been able to re-acquire in the archives, I got into a discussion about sharpening. I was about to try to convex the edge on my M43, and promised the folks I was talking to (whose names I no longer remember), that I would post some pics. As you may surmise, I forgot to do this.....in part because it took so long to get around to the sharpening task in question!:o

Well, I finally did it. In the few days before Christmas, I simply sat down, and re-sharpened both the kuk and the karda with my Altoid Kit, the task involving several hours' work, and using up a lot of 220-grit sandpaper!

So, here are the pics of what the edge looks like now (replacing the "microbevel" I'd gotten touched up at the sharpening shop):

4212042572_168e092e21.jpg
4212042180_e841fac560.jpg

4211278763_1d68963b1a.jpg
4212040072_de866df854.jpg

4212039442_97752fc8d2.jpg


So, my friends, wherever you are, my promise to you is fulfilled!

Merry Christmas.
 
I didn't do it all at once (two hours is about the most time that I can concentrate on anything), but I sat through 2 movies on DVD, just in the time it took to use up the 220-grit. Add in the time spent with the finer grits (which didn't take very long, by comparison, thanks to the convexity), I'd say that the entire process took at least 4 hours.
 
how tough is it to touch up a convexed edge in the field and whats the benefit of it over the stock trim?
 
What I've just discovered is, that using the sharpening method that I favor (mousepad and sandpaper, attached to an Altoids can), a convex edge touches up very quickly. That, indeed, seems to be a principal advantage, and I'd note that this is how several of my HI blades, including my Sher R6 and Bura Salyan, came out of the box. Also, it certainly looks better than it did before I reshaped it.
Now, many people seem to feel that the convex edge (especially if a shallow one) has innate advantages in cutting, supposedly combining sharpness and edge-holding very well. But I haven't tested that yet, personally, so there will be more news as it comes. There will be news, however, with more chopping work and test-cutting after the Christmas/New Year's holiday. (I have a ton of plastic bottles stored up.;)) In the meantime, the edge's ease of maintenance, alone, is a strong justification, at least as far as I'm concerned.
 
Wow, did 'er by hand... no surprise it'd take so long. To any HI outsiders, these babies have a LOT of steel, and reprofiling can be labour intensive. Heck, even using a belt grinder, it can take me 30 minutes or so to get the less keen specimens roughly where I want them.
 
...never mind how tough this steel can be: I've seen it simply laugh off the presence of a file, to say nothing of any attempt to etch it!
 
Hi Nicholas!

What is this Altoid kit sharpening method you talk about? all I come up in google search is just a survival kit inside the altoids can, can you explain?

Thanks!
AlexGT
 
A standard hard rubber school eraser with sandpaper cut to fit works extremely well and will conform to the curve of the convex shape you wish to achieve. I've got an edge that will easily cut paper with no effort.

Very easy to maintain in the field, first with the Chakma and then 1500-grit paper.
 
An eraser: I hand't thought of that. Good suggestion.

Meanwhile, here's a link to the post that showed me how to make the Altoids kit.
 
The Chef said:
how tough is it to touch up a convexed edge in the field and whats the benefit of it over the stock trim?
Click to expand...

One benefit of the convex edge is that its easy to touch up in the field. You can just lay a piece of sandpaper on your thigh (be careful!) or make a contraption kinda like this:

HH2.jpg
 
That's about right; mine uses rubber bands, though. Meanwhile, somewhere on the 'Net, I found someone who'd rigged up something like UD's kit, and had even drilled holes in the sides, to hold rolled-up strips of sandpaper!
 
Thanks to everyone for all the great ideas and pictures. A great help to newbs like me, since I'm deficient in sharpening skills.

Rick
 
I didn't know squat when I came here, either, and the Altoid Can Kit (A.C.K.) is the first method I've been any good at! All it took was trial and error....and a LOT of sandpaper!
 
Awesome work Nicholas!

As to not dishearten those thinking about convexing their khuks, I'll add that the length of time it takes definitely goes down with experience. The first knife I ever gave a convex edge was my BK-2 and that took me a good 3 or so hours of trial and error before getting a razor sharp edge that I was pleased with (and this is with a good bit of experience freehand sharpening on japanese waterstones). My first khukri (a 15" Ang Khola) took me about two hours to get razor sharp. After that, I got an 18" Vojpure and an 18" m43 done in about an hour. Touch-up on any takes ~10minutes.

The process is definitely a lot cheaper than using waterstones (a mixed pack of wet&dry sandpaper ranging for 220-1000grit is less than $5 and a mousepad can be had anywhere for free) and leaves an edge that lasts longer and IMO is easier to touch up than a V-edge. And to dispel the myth that convex edges are inherently duller than V-edges, my m43 is capable of shaving :p

P1020334.jpg
 
My current (imperfect and evolving) understanding is that convex edges are good for choppers for two primary reasons:

- Highly polished edges achieved with stropping last longer, since at the microscopic level a stropped edge is much less jagged and doesn't catch and tear out as much. (This implies that if you convex, you should strop to gain this benefit, and not simply stop with sandpaper).

- Convex sharpening technique doesn't have a propensity for raising a burr, and in fact very nicely gets rid of the burr if you strop a stone-sharpened edge which hadn't been de-burred, as it were. Thus, even a beginner can easily attain a clean burr-free edge, rather than have the burr flop over and flatten as might happen with incomplete stone sharpening (e.g. no burr removal / microbevel pass).
 
Last edited:
starboard said:
- Highly polished edges achieved with stropping last longer, since at the microscopic level a stropped edge is much less jagged and doesn't catch and tear out as much. (This implies that if you convex, you should strop to gain this benefit, and not simply stop with sandpaper).
Click to expand...

Agreed, and luckily, the A.C.K. does have a stropping leather glued on, opposite to the sandpaper.
 
starboard said:
My current (imperfect and evolving) understanding is that convex edges are good for choppers for two primary reasons . . .
Click to expand...

Well the main reason convex edges are better for choppers is because arcs are inherently stronger than straight lines - it's why just about anything we use that has to endure high pressure/forces are either cylindrical or spherical - the shapes disperse force better. For convex knives, the arcs also gives the edge more metal behind it, increasing the area for which the force from the impact can be dispersed and lessening the chance of edge deformation (Think about how a concave or "hollow" grind - which has very little metal behind it - would react after suffering a hard impact).

Physics aside, you are correct to say that the technique for convex edges makes it easier for a beginner attain a sharp edge. Not only does it help minimize the bur, but you also do not have to be as concerned about angles (though maintaining about a 16-18ish angle and knowing to not using much pressure does help). While a properly done flat or hollow grind will always be "sharper" than a properly done convex grind, I've found the the benefits of a convex grind to far outweigh that for most applications :thumbup:
 
You must log in or register to reply here.
Back
Top