tests for sharpness

[getridone]

What do you guys like to do to test for sharpness (besides shaving hair). Seems like push cutting paper is pretty common, but is this really telling me something meaningful? Sometimes I wonder what the limits of my blades are. After watching a video with Jerry Fisk using a BK-5 doing some impressive feats I tried the same around my house, with my 5, but with much less impressive results. I set up a cardboard tube like ol' Lyn C Thompson on those Cold Steel videos does and tried to slice through that sucker and was rejected, I subsequently tore my clothing and screamed at the gods of knife sharpening. One day I'll get it...sigh.

 

[richard j]

i tested a knife i made by doing this http://knifetests.com/kII.html
i have also cut kevlar gloves in half or just the fingers with short blades.

 

[Obsessed with Edges]

I've gotten into a habit of testing mine on phonebook paper. If it slices cleanly and repeatedly through the page, from heel to tip, without snagging (burrs/wire edges) or slipping (dull/blunt), I know it's good to go. The paper is thin & flimsy enough to reveal very fine burrs and wire edges, which will hang up and cause the paper to bend/fold out of the way. Sometimes stiffer paper will still cut, without indicating some of the finer defects in the edge. Cutting phonebook paper is certainly not the most impressive test, visually, but it has been reliable for me in verifying the overall good condition of the edge, suitable for most real-world cutting tasks.

I highlighted 'repeatedly', above, because a wire edge will often seem very sharp initially, and shave hairs and such, but will quickly fold over when cutting most anything else. It can be deceptive, if one doesn't test beyond shaving hairs.

Here are a couple of other threads on the topic, with some of the more 'fun' ways to test sharpness:

Recent thread:
http://www.bladeforums.com/forums/showthread.php/921364-Completely-Sharp

Considerably older thread:
http://www.bladeforums.com/forums/showthread.php/554632-Sharpening-Record-Page

 

[Magnaminous_G]

I've gotten into a habit of testing mine on phonebook paper. If it slices cleanly and repeatedly through the page, from heel to tip, without snagging (burrs/wire edges) or slipping (dull/blunt), I know it's good to go. ... I highlighted 'repeatedly', above, because a wire edge will often seem very sharp initially, and shave hairs and such, but will quickly fold over when cutting most anything else. It can be deceptive, if one doesn't test beyond shaving hairs.

+1000

This is very common. Needs to push cut something (phonebook paper sounds great) repeatedly, then you know the edge is real.

 

[Mack]

i tested a knife i made by doing this http://knifetests.com/kII.html
i have also cut kevlar gloves in half or just the fingers with short blades.

This was what really sold me on Richard's sharpening. When we cut the fingers of a kevlar glove and the blade was still sharp afterward. I also learned not to rely too much on "cut resistant" gloves.

 

[james terrio]

To me, shaving hair and slicing newsprint cleanly are the starting point for any cutting tool. (phone book paper makes a lot of sense too, as David explained; it will quickly show you if there's any rough spots in the edge.) I mean an EDC, fighter, camp knife, 'hawk, felling axe etc should all be able to do this.

Beyond that, it just boils down to what you're going to cut most often with that particular blade. A felling axe needs a bit thicker edge than a knife that's only used for caping trophies, for obvious reasons. Good steel and heat-treat allows us to keep edges thinner than they need to be, without sacrificing toughness. But there's a point where crazy-thin "novelty edges" just get silly, unless all you're going to do with your knife is sit around and split hairs.

 

[never too sharp]

I use whatever paper I have on hand.

 

[knarfeng]

I rest the edge on my fingernail at 20° - 30° angle. If the knife edge catches on the nail and won't slide under its own weight, it's sharp enough.