MadSci Network: Engineering

Re: Are laser-shurpened knives sharper then regular knifes?

Date: Sun Mar 7 18:51:00 1999
Posted By: Steve Guch, Post-doc/Fellow, Physics (Electro-Optics/Lasers), Litton Systems, Inc., Laser Systems Division
Area of science: Engineering
ID: 920015196.Eg

Your question is a good one, and the answer probably has more to do with how 
things are marketed than science and technology.

While I have been working with lasers for over 25 years and have fairly broad 
experience in their applications, I am reasonably sure that there is no 
industrial process which uses lasers to sharpen or hone a knife blade.  While 
lasers are sometimes used to heat-treat metals to make them harder or to create 
special alloys in localized areas, I don't believe that this is being done 
commercially with knives.

I think that the term "laser sharp" or "laser sharpened" has the same meaning 
when applied to knives that it does to fishing hooks -- except that hooks have 
very sharp points whereas knives have very sharp edges.  In the case of "laser 
sharpened" fishing hooks, the points are ground to a very sharp state using 
conventional grinding processes -- I think that they use a carborundum abrasive 
held into wheels or cups by an epoxy binder, much like the grinding wheels used 
in machine shops to sharpen tools used in standard machining or like the 
carborundum "stones" used to hone knife blades.  "Laser sharp" fish hooks are 
then processed using a chemical etching process -- proprietary to each 
individual manufacturer, but almost certainly using a mixture of acids -- to 
remove irregularities or burrs in the surfaces and so make the edge more 
perfect... sharper.

The reference to being "laser sharpened" is, I believe, a marketing or selling 
term which alludes to the blades being very accurate and precise -- like a 
laser beam used to point precisely and very accurately.  I believe that the 
alloys used to make such knives are pretty much the same as those used to make 
other knives, and that laser heat treating is not used to make the metal 
harder...  As far as I know, the sharpening process should not make the blades 
stay sharper any longer than any other knife blades of the same general design.

On the other hand, there are things that can and are done to commercial knife 
blades that make them cut better for longer.  Serrated blades -- the ones with 
little curves in the edge -- tend to cut more readily than conventional 
straight blades, probably because the serrations result in the blade resting on 
the material being cut in only a few places, so that more pressure is put on 
those points and they cut more rapidly in a sawing action.

The only new technology that I've heard about to keep blades sharp for an 
extended period of time is coating the blades with a thin layer of a very hard 
material -- typically a transparent coating of diamond-like carbon is used -- 
which prevents the metal from being abraded by the materials being cut.  The 
DLC is so hard that it isn't abraded or scratched by most normal materials, so 
that it lasts for a very long time.  DLC is applied by putting the blade in a 
high vacuum and then evaporating carbon in a special way so that it coats the 
blade with a very thing diamond-like coating rather than just sooty black 
carbon.  I don't know of any knives that use this approach, but the Gillette 
Mach 3 razor uses it and -- since I use one -- I can tell you that it really 
does last a very long time and give a very close shave...  The closeness is due 
to how well the blade is sharpened using a conventional grinding process and 
the life is due to the diamond-like carbon coating.

So that's about it...  Laser sharpened blades are, I think, a marketing 
construction designed to give you the impression that the blades have some of 
the precision of a laser beam, but the process is totally unrelated to lasers 
and any enhancements in life are not due to laser processing.

Thanks for your question:  I had heard about these things but had never really 
thought about them or did any research on them!

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