Sharpening a Convex Edge!!!?

P

PC356

Joined
Jun 10, 2005
Messages
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I am having hell putting an edge on my Howling Rat. I have tried for hours using 800 and 1500 grit 3M Wet/Dry and a mousepad for backing and can put the best looking mirror polished edge on this thing you ever saw. Only problem is it won't cut warm butter. What might I be doing wrong? I was under the impression this was a very forgiving method of sharpening. Should I start with a lower grit. This particular Swamprat came very dull for some reason :( . Please, I am dealing with a dry socket wisdom tooth while trying this so naturally I am very frustrated. Oh, well off to the dentist to see what he can do. :D
 
If the edge is thin enough, you should be able to maintain a convex edge with traditional flat bench stones. The way i put a final edge on most of my knives is roll a convex edge in establishing a "burr" that will flop back/forth with your finger. You simply then either strop the burr off, or use flat stones to remove the burr. You do not try and re establish the convex roll, but only work the very edge.

If the convex edge is too thick, you pretty much need a slack belt or rotary platen to re sharpen properly. These thick convex edges wont allow the proper angle for the use of a flat bench stone (roll is too steep).

Im sure most if not all of this is covered in the thread referenced by ddean.
 
Before using more abrasives, in the interest of not removing more metal than needed try steeling the edge then stropping a bit, it seems that you're having the same problem I do with sandpaper, and that's probably using too much pressure or too soft a backing, and rounding the edge off instead of sharpening it.
 
all very good advice.


only thing I can add is to run a black marker down the edge before you sharpen to see where you are making contact with the blade while you're sharpening. Ideally, you would "wipe" off the marker evenly.
 
You may be pressing down too hard on the mouse pad. If the surface is too soft the material actually wraps around the edge and reduces its sharpness. Try a lighter stroke or a harder surface. You want to work on the bevel and not the exact edge. Some of the experts recommend using a piece of leather glued to piece of hardwood.

opps - just reread a previous response. I agree with what he said.
 
Still having a bear of a time with this method. Can't even get the Howler to scrape hair off my arm. I have tried firmer backing mediums, experimented with different angles, used heavier and lighter downward pressures, tried various grits and still the same dull ass knife. Thombrogan from here and the RAT forums was kind enough to put together some Dan Koster sharpening footage on one of his kukhuris to help me out a little. But the methods he used were quite a bit different than the sandpaper mouse pad technique. Interesting nonetheless and very appreciated. Anymore bright ideas? I am not going to give up on this method until I get it it. At this point I would even pay someone to burn a dvd showing all the little nuances and little idiosynchrocies of the method. Man, I feel like a moron because I am having such a hard time with such a supposedly easy method. Please give me some advice if you have it. I have searched and tried to apply what I found to my efforts but to no avail. Thanks fellas.
 
As Mr Koster posted above:
USE MAGIC MARKER TO TELL YOU WHERE YOU ARE REMOVING METAL.

1. color the edge with magic marker
2. stone/strop/abrade/polish the edge
3. look to see where the magic marker is GONE
(Where the marker is gone is where you were removing metal.)
4. repeat steps #1-3 until you're happy with the edge

This is the single best trick for sharpening any edge. It tells you in a very empirical way whether or not you are sharpening the very last little bit of your edge, which is the part that actually cuts for you.

BTW, I find the Busse/Rat edges pretty thick too. That gives them some of their great edge strength and durability. But it doesn't make them exceptional slicers.
 
PC356

You are trying to get 'C', but are finishing up with 'D'.


Convexedge.jpg


And I think the reason is too much pressure on the mouse pad so that the edge is rounded over as below

foamback.jpg


Definitely try the black marker trick to actually see just what is going on.

And get ride of the mouse pad when working on the actual edge.
 
PC356 said:
Still having a bear of a time with this method.
Click to expand...

Switch to a differnt one. Take a very coarse benchstone, hog the material off to create an edge of 10 to 15 degrees per side depending on how rough you are going to use it, then apply a small microbevel at 20 degrees with a sharpmaker or other v-rod. The initial profile takes 1-2 minutes with a proper stone (220 SiC waterstone), and the v-rodding is a few seconds.

What is likely happening with the sandpaper method is you are either not actually hitting the edge or you are leaving the edge burred. Since it is a trailing motion they remove burrs really weakly. If you want to stick with this method get a cheap 10x magnifier and check the edge and make sure the initial coarse grit is actually hitting the edge.

-Cliff
 
I TOTALLY agree with Cliff on this. Get the 10X Loupe where you can actually SEE what you are doing to the edge. That and the marker tells you right away, too steep, too shallow, too hard, too soft ... Whatever.

Look at the edge with the loupe. Make a couple of passes with whatever, look at the edge again. You can tell right quick if you're in the neighborhood, much less the right street and the right house.

That loupe will be the best piece of sharpening equipment you will own. Nothing like being able to see what's really going on.

Rob
 
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