A good indication of sharpness?

J

jzmtl

Joined
Jul 29, 2007
Messages
434
Just wondering, what's a good indication of how sharp a knife it? Is slicing a piece of paper like they do on sword infomercials (come on, you must've seen those) a good indicator or is it load of crap.

No I'm not gona try shaving myself with the said knife to see if it's sharp. :eek:
 
Start the cut on whatever the knife has to cut with very little force and/or movement.

-Cliff
 
It's a pocket knife, so it really dosen't have anything specific to cut. I tried the shaving method before, lost some arm hair, gained razor burn for a day, have no intention of getting any more.
 
Welcome to Bladeforums!

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I read about another 'test'. Rest the knife blade on your angled thumb nail, if it slides off it's not sharp, if it bites it is. The higher angle you hold, the sharper the knife has to be in order to bite.

You could also use a plastic pen instead of your nails.

I've heard that a reasonably sharp knife should bite at at least 60 degrees, and a sharp knife at 75 degrees+.

Beats shaving your body hairs, IMHO.
 
Chopping the bottom half off of a fine 3-4 inch long hanging hair is the test I use. Notch a sliver of soft wood to hold the top of the hair. Let the hair dangle vertically and swipe at it horizontally with your knife.

BTW: I use this test with everything: kitchen knives, even my old Boy Scout hatchet.
 
Xipe said:
I read about another 'test'. Rest the knife blade on your angled thumb nail, if it slides off it's not sharp, if it bites it is. The higher angle you hold, the sharper the knife has to be in order to bite.

You could also use a plastic pen instead of your nails.

I've heard that a reasonably sharp knife should bite at at least 60 degrees, and a sharp knife at 75 degrees+.

Beats shaving your body hairs, IMHO.
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To me it sounds like you got it backward, shouldn't a sharper knife be able to bite at lower angle than dull knife? I mean even a dull knife would bite at near vertical, say 89 degrees.

As for hair, mine's is barely 1 inch long so that's no go. :D
 
jzmtl said:
To me it sounds like you got it backward, shouldn't a sharper knife be able to bite at lower angle than dull knife? I mean even a dull knife would bite at near vertical, say 89 degrees.
Click to expand...

A pen held upright is at 90 degrees to the surface. :confused: If I was unclear, the numbers were the angle you hold the test rod/thumb at.
 
I used the arm hair shaving test for a long time. I don't bother with tests anymore because I always get the same result, it shaves. :).
 
Slice through thin air quickly. If your knife is sharp, you should hear a snap as the air molecules come back together.
 
Since I have lots of paracord, I always keep a 12" or so length on the bench. Now, I don;t use this so much as a test for sharpness as a guage for consistency. I lay the paracord down on a short length of mahogany or redwood and, starting near the tip of the blade, push straight down into the paracord slicing all the way through. Then I move down the length of the blade every 1/8" or 3/16" or so doing the same thing.

After doing this awhile, you'll get a feel for how much pressure it takes a sharp edge to slice through as opposed to a semi-sharp edge. You can feel and hear the blade cutting through the paracord. Sometimes I'll use leather too. A 6" length of 8oz, about 1/2" wide, standing on edge. A knife that will "pop" hairs on my arm 1/8" above the skin will literally glide down through the leather, slicing a nice thin piece off the end.
 
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