Sharpening Convex edge - success!

Daniel L

Daniel L

Gold Member
Joined
Nov 2, 1998
Messages
1,999
I just thought I'd pass on a tip - I have a Spyderco Moran (first series with mirror polish and convex edge) and a HI khukri - and I've always struggled on how to restore the convex edge without resorting to going to standard bevel.

I've read the sharpening about FAQ about using a piece of wood covered with leather for some "give" or other alternative methods - but I found a great solution that is cheap and easy.

Basically I bought a "sanding block" from the hardware store. (Its a 6" x 3" block of wood with a thin layer of rubber foam on one side.) Then with some 300/800/1200 grit sandpaper (the black waterproof stuff) I "push" the block off the edge at a low angle - the rubber foam under the sandpaper conforms to the convex edge and sharpens up nicely! (I hold the blade in my left hand with the edge facing away from me.)

I push the block with sandpaper off the blade perpendicularly - so you can work a 3" section at a time. I didn't think a "wire edge" would appear so I turned over the blade at some time and then I "pull" the block over the edge to sharpen the other side (ie the knife is in my left hand with the edge facing me.)

This probably isn't new - but now I have a hair popping sharp Spyderco Moran and a darn sharp khukri!



------------------
Daniel
 
Cliff Stamp turned me onto this technique a while back.

I bought a nice, flat, "finish grade" 2"x4" and whacked off a piece about 16" long I guess.

I found two old computer mouse pads that were same thickness, neoprene rubber on one side and a cloth like backing on the other.

Cut them to size, glued to 2"x4", and voila, convex edge sharpening system given some 400 grit and then 600 grit sandpaper (autobody wet or dry). I just loop the sandpaper underneath, but oughta come up with a better way to anchor it I suppose. That is the tradeoff vs. sanding block....sanding block anchors paper well but is small for bigass 12" Bowies. The 2"x4" is long enough but I need to adapt an anchoring mechanism somehow.

Cut some little "no slip" feet outta the same mouse pads about 1" square and glued to the base.

Takes a bit of practice, but I can get a good but not wicked shaving edge. Just need more practice I'm sure.

 
rdangerer:

<font face="Verdana, Arial" size="2">I can get a good but not wicked shaving edge.</font>
Click to expand...

A couple of things come to mind. First off if the blade has seen heavy use there might be a lot of weakened metal along the edge with rounded or broken out carbides. Even if this is reshaped and ground well, the performance is going to be fairly poor. This is why every now and again I reshape flat bevels with either a SiC waterstone or Diamond pads to make sure the edge is fresh. For convex bevels get some really coarse Diamond dusted paper or Sic and grind a little beyond what is necessary to form the bevel. This is not necessary all the time, but has to be done on occasion if the blade sees heavy frequent use.

The other fact is the method itself. If you vary the pressure, the contour on the pad changes and the resulting edge quality goes all over the place. I spent some time working on a scale initially until I was confident that I was using smooth constant strokes. The other part of this is to make sure that your grind lines cross over each other. If they run parallel you can leave a wispy piece of really broken up metal that will prevent high performance. The last factor is the quality of the sandpaper, Lee Valley sells high quality SiC sandpaper on Mylar backing up to 1000 grit. That is what I use for finishing high alloy blades (1095 class blades are readily cut with much lower grade AO paper). The 1000 grit SiC will leave a very fine edge on all the blades I have tried it on. It isn't a completly smooth finish like a CrO buff, but will push shave with the lighest of pressure on fine hair, and can cut freestanding coarse hair with ease. It also has enough bite to shred soft ropes, and can slice decently well on the harder ones, while still being decently durable for heavy chopping impacts. A CrO buff would be best for chopping, but pretty much tends to mangle slicing ability.

-Cliff
 
For some more information on sharpening convex ground edges click on the following links from the "Marble's Arms Forum" over at KFC.

http://www.knifeforums.com/ubb/Forum56/HTML/000010.html
http://www.knifeforums.com/ubb/Forum56/HTML/000022.html
http://www.knifeforums.com/ubb/Forum56/HTML/000211.html

*Note-Jason Stewart (ex-employee of Marble's Knives & son of Mike Stewart) answers many questions as to the sharpening techniques that he recommends for Marble's knives.

--The Raptor--



[This message has been edited by Raptor (edited 06-07-2001).]
 
You must log in or register to reply here.
Back
Top