Isn't there some kind of 'sharpness index'?

[trains are bad]

I know we all have our 'sharp, shaving sharp, scary sharp index' that is mostly based on how easy it is to shave hair.

But I was reading "the hot zone" where there was mention of a tiny blade that was used for slicing up blood cells, that was so sharp that if you cut yourself with it it would ruin it because it was like super precise.

It got me to thinking that there was surely many industrial applications for sharp blades, in vegetable slicers, plastics cutters, all kinds of stuff. Surely there is some 'engineering speak' way to express sharpness? Like a 'sharpness scale' or some unit of sharpness? Surely when designing precision machinery or ordering surgical tools, they don't specify blades "sharp enough to shave arm hair with only light pressure" or something.

There has to be some objective way to express sharpness, no?

 

[Cliff Stamp]

There has to be some objective way to express sharpness, no?

Yes, back in 99 I was discussing this with Wilson who noted when he did rope cutting he measured the force so as to determine sharpness without judgement, an idea he got from Goddard who does a lot of rope cutting juding steels and abrasives.

I started it then and found it useful, but very imprecise because much of the force was due to the side load and not the edge load which is the sharpness. Thus I started cutting thread which has no side load and measures sharpness almost directly.

After doing this for awhile I realized it was only half the picture and just determined push cutting sharpness, and thus started slicing light cord under tension and measuring the length of edge so as to determine sharpness on a slice.

There is no judgement in this, it just gives you two numbers. It isn't the entire picture though, as I found later on that the 3/8" hemp draw should also be included as well because large scale micro-teeth can produce a very sharp edge for thick rope cutting, but not do as well on the thread and cotton.

-Cliff

 

[t1mpani]

I know that my what-it-feels-like-to-be-cut-by-it scale goes, from sharpest to dullest:
1) "Hey, when did that happen? I sure didn't feel it..."
2) "Oops! Have to be more careful."
3) "Ouch!"
4) "Okay now, son, you really don't want to do what I'm doing here. See, this knife is way too dull, and you have to be careful pushing hard on it like this because it can get away from you suddenly. It takes a lot of experience working with sharp tools to develop the judgement that will allow you to safely determi--
AAAAAAGGHHHH!!!! SONUVA MUTHA F#@*ING %*&@..... "

 

[Jeff Clark]

"Sharp" for a diamond microtome blade is when the radius of curvature of the edge is about 12 carbon atom diameters. On the other hand the standard included angle for the edge faces is 45 degrees:

http://www.microstartech.com/index/diamondknives/diamondmanual.htm