Rough convex edge vs. Fine convex edge?

T

The Big Kahuna

Joined
Sep 15, 2002
Messages
183
A bit of advice requested from the experienced "convex edgers" on the forum.

I just read a knife review where the reviewer used 3/4 inch manila rope to test the knife's edge for different sharpening methods. He started with a worn 400 grit belt + Jeweler rouge strop (hairp popping edge lasted only four cuts). Next he tried a new 320 grit belt (7 cuts). And finally a worn 150 grit belt (50 cuts and it still could cut arm hair). I take it that the worn 150 grit belt produced the best working edge for this example because of the grain of the "saw tooth" edge it created.

Many on the Forum have suggested the 600+ grit sandpaper on mousepad/belt followed by stropping with rouge or chromium oxide stuff.

In comparing the 600 grit + rouge strop "fine" edge to the 150 or so grit "rough" edge for the following two khukuri/karda uses, which edge is better for a) effectiveness of the edge for the job and b) durability of the edge during repeated use? (i.e. which edge is better for which job and why?)

Job 1 - The food chopping, game gutting and skinning, and light chores (cutting cloth, string, rope, etc.) of a camping knife?

Job 2- The woodchopping and brush clearing of a machete / axe?

Many thanks in advance for the wisdom!
 
It depend on what kind of things I have to cut. For my 18" Ak I keep a "rougher" edge. I went to to only 600 grit paper. Which in my opinion isn't really that rough at all but I feel that it is something that is easy to maintain. I have a knife that I use to cut rope and only take it to about a 220 finish. It will kind of shave hair but will cut rope like nobodies business. The saw tooth effect is very real but not great for push cuts, think straight razor. I took the Karda for my AK up to a much more polished edge. I went to 2000 grit wet/dry paper and then finished it up with a strop. It will push cut, shave hair etc., very, very well. For food /game prep I would rather have a fine polished edge. If I have to choose one knife and only one knife that will be used for everything I will tend to go for a polished edge since I feel that it will cover more kinds of cuts. In either case a convex edge will tend to hold up better. I think that it is by far the best for any kind of chopper be it machete/axe or khukuri, it will hold up longer and cut better. I wouldn't have anything else. Sorry if this is long and I hope it somewhat covers what you asked. Pendentive needs to get in on this one.
 
I need more information. Are we talking about Cliff's "controversial" rope cutting tests? If so, that's an entirely different matter.

But I can comment on something that doesn't always get figured in: belt abrasive types.

You have basically 4 types of belts:

Aluminum Oxide - J weight
Aluminum Oxide - X weight
Silicon Carbide
Blue Zirconia

A 120 grit belt would perform 4 different ways in each of those 4 types.

The Blue Zirc. is somewhat flexible and in my opinion, best for putting on a convex edge on a khukuri. After that, the A/O J is best for finishing it up - it is very flexible and inexpensive.

A/O X is too heavy/stiff - best really for profiling a new edge, and not for bevel grinding.

Silicon Carbide at the high grits is great for sharpening and polishing.


Take all of that and add to it the idea that you can make a 120 grit belt behave like a 400 grit belt by wearing it out and using gentle pressure. I have (nearly) mirror polished a khukuri to a shaving sharp edge with only a 120 grit A/O J belt. Start out pushing hard, end by lightening up.


Personally, I subscribe to this idea somewhat and that's why I stop at the belt grinder after 180/220 grit (usually) and go to hand sanding. Sanding by hand removes much less steel. Just polishes the teeth. :D

However, it also makes it so that you can achieve a push cut.

With each villager I worked on, after sharpening it, I cut a 2x4 in half (some, more than once) and afterwards tested the push cut. All have retained their edge. (See Bruise's test on the CD)

4 out of the 5 ABS cutting competition competitors (Blade 2003) used a ceramic rod as the final sharpening method before the competition which involved cutting free-hanging rope. :confused:


Tests like the one you mentioned are very valuable in understanding how blades perform in a closely controlled experiment. However, very few people carry a knife for each task at hand and end up needing only one or two to get 90% of their stuff done. So don't forget to put the tests in perspective of your personal usage.



Job 1 - The food chopping, game gutting and skinning, and light chores (cutting cloth, string, rope, etc.) of a camping knife?

Polished edge.


Job 2- The woodchopping and brush clearing of a machete / axe?

Either polished, or rough-polished.



Dan





p.s. I'm sure I've left something out, but it's lunchtime. :D
 
Feth covered it, but here's the 'why'--the miniature saw teeth do aid greatly in slicing soft materials, but they'll break off under impact (think of taking a wood saw and trying to chop with it), leaving little chips in your edge. For cutting up meat and such, a rougher edge will make it go a lot faster. If you're planning on using a khuk or big bowie to chop through joints and stuff, a polished edge is what you want. Overall, unless its really a small one or intended as a weapon for slashing attacks, I don't think you'd want a toothy edge on a khuk. I'd do a polished khuk and a toothy karda. :)

Edited to add: Seems Dan beat me to it. I'd trust him more anyway. :D
 
pendentive :

Are we talking about Cliff's "controversial" rope cutting tests?
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No, I have done that kind of thing, but exactly with those belts. The above just shows the increase in cutting ability and edge retention of a coarse edge in slicing. Basically the more coarse the better, up until about 80 grit AO or so, the performance degrades after that. 40 grit ZO is horrible. You see the opposite performance for push cutting, as noted. Here you want the highest polish you can get. It will cut the best and stay sharpest the longest.

-Cliff
 
Not to toss sour grapes but this quote always made me chuckle:

"I have never been attacked by a rope or a stump."

Paul C., 14 year HI khukuri (about 15) owner, specops operative with missions to all world hot spots for a dozen years. Now retired.
 
Thanks to all for the wisdom (yes, even you, UB :rolleyes: !). I'm going to try a rough edge on a 0.08 inch thin, 3 inch blade pocket knife I have.

Anybody know where I can get 100-200 grit compound to put on a leather strop?
 
Originally posted by The Big Kahuna .....Anybody know where I can get 100-200 grit compound to put on a leather strop?
Click to expand...
Might try industrial supply for blast abrasives of different grits.

Picked up some "Blast Abrasive - Fine" that I think was intended
for air blast cleaning of spark plugs.

I'm sure it's not less than 200.
But it was the 'fine'.
 
"I have never been attacked by a rope or a stump."
Me neither, but one night back in '75 I decided to give streaking a try and got taken out by a bush that was slightly less than waist high.:eek: :(

Sarge
 
Other local sources would be suppliers for:

jewelry making/repair
lapidary (rock polishing)
Rock (marble, etc) counter manufacturers/installers
 
Guys, y'all do whatever works for you. My personal preference in mediums for putting a "toothy" edge on a knife are the diamond hones produced by DMT or EZ Lap. They're rugged, easy to carry around, and come in a variety of styles and grits. A good diamond hone and a ceramic rod should be about all the sharpening supplies you need in a deer camp, unless you plan on using your knife to shave with.:D

Sarge
 
Thanks for all the words of wisdom. I'm gonna try some cheap, easy ways until I can find some grit: getting some 150 sandpaper and sticking on the pad I used for the 600, and I'll give a ceramic rod a go.

By the way, Sarge, your pics on boar bow hunting in Texas inspired me to try it out in Malaysia next door. So I've been practising with a compound and a bare bow recurve (the recurve can be broken down and carried "discreetly" into the plantations - I prefer the recurve if I can get my accuracy up). I've been told that the pigs in Malaysia mainly feed on palm oil fruits from plantations which cover most of the country. So their supposed to be good eating (and since most people are Muslim they can't touch or eat boars anyway). Saw one on a night hunt the other day, but my friend missed :( .
 
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