Sharpness: can it be deceptive?

I find there are some knives that do not feel extremely sharp, but depending on what they are cutting, they behave as if they are. And occasionally there are knives that feel almost razor-like, but do not cut well at all.

With my Spydercos I haven't had any problems with cutting. I DO find (for me) that the new ('98) versions of the Delica/Endura seem to cut nicer than the older versions (I think due to wider blade/thinner edge).

One of my 3 Enduras (1 original, 2 '98s) is a plain-edged '98 I've had a couple years. When I bought it I felt it was sharp but not up to what I expected so for a while, off and on I would experiment and resharpen with the 203. It's sharper, but does not feel "razory" like my plain Delica or even my SS plain Police (which has a slightly thicker edge). It doesn't shave arm hair as easily as some, but it cuts very nicely, and touching the edge length-wise it has the (stickier) feel as opposed to a slippery, smoothe feel, indicating micro-teeth for better cutting.

I'm a bit puzzled. Is this a common type of phenomena, where visually similar edges will vary in performance based on the taks/materials cut?
Jim
 
Matt Shade

Matt Shade

Joined
Nov 24, 1999
Messages
4,981
From my experience you should not drag your thumb over the edge to test for sharpness. Not because of the usual its not safe stuff. It fools you. If its truly sharp the edge will be smooth enough that it won't really bite at your skin until its slicing through it. So it won't really feel sharp because its just kind of sliding along. A really dull edge will do the same thing. An edge that is just starting to get sharp will have some bite to it because the edge is getting thin, but its no very smooth yet. And theres the possibility of wire edges.
I start out and judge and edge by how it looks. Both bevels should be mirror polished. Hold the knife up so that the edge on one sise catches the light. Slowly turn it so that the edge is facing you and the then the opposite bevel is. YOu should not see and light reflecting off of the edge itself. Both bevels should reflect lots of light, but there should be point when your turning it when you don't see any light reflecting off the edge. If it looks like that, then I try some other tests like cuting paper, shaving,etc.

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I may not be the sharpest knife in the drawer... but I've got the sharpest knife in the room.
 
Absolutely this happens. Here's my theory as to why.

A razor-polished edge will grab when you drag your thumb across it (perpendicular! don't slice yourself), whereas a coarser-grit edge won't.

A coarse-grit edge will slice like crazy, where a razor-polished edge won't.

I always do a few tests when I'm done sharpening. One is to shave a little hair off my arm. The other is to slice some hard poly rope. This gives me an idea of how the blade does, both push-cutting and slicing. I can fine-tune the grit based on what I'm going to use the knife for. Because I always do this rope test with the same kind of rope, I know exactly how the final edge should perform (should it go halfway through the rope? 3/4 through?). I also push-cut through the rope to see how it does there.

Joe
 
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