The True Measure of a knife's sharpness

golok

golok

Joined
Oct 20, 2000
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Apart from the "shaving your arm" standard, is there a truly undisputable measurement of a knife's sharpness?

I have been told there is a "floating tissue" measure, which may or may not be accurate.

What I am thinking of is whether there is an instrument whereby a knife's edge can be measured scientifically, like measuring the weight of cigarette smoke.
 
I've always used the "fingernail" test. If the edge "grabs" your fingernail, rather than sliding off, it's sharp enough. The plastic edge testers marketed by the Razor Edge sharpening folks work on the same idea.
 
If you want to put a number on how sharp a knife is, just cut something and measure how much force it takes. Note that every cutting test will be influenced by the edge geometry to some extent. The smaller and looser the material, the less this extent will be.

The CATRA group has a machine which does this with great precision. Basically it pushes a knife through a stack of cards and measures the force required. The initial performance can be used as a measure of sharpness, however it will be significantly effected by geometry as the stock used will exert significant binding forces on the edge.

-Cliff
 
I use the same test as Razor, but another test is to look close at the edge. If you can actually SEE the edge, it's not sharp enough.
 
I sometimes use the plastic bag test. Just take one of those plastic grocery bags and see if the edge will split it easily. Everyone I know has tons of the things around. Its the same as cutting paper, just a much thinner, more flacid material.
 
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