What is a sharp knife??

What is Sharp? - The argument for Micro-serrations

 

I once had a very heated debate with a school-friend about whether his knife was sharper than mine, (yes really, one of those discussions, but we were not at school so no rules were broken). The discussion boiled down to the fact that his knife had a rather coarse angle of bevel and it had been sharpened with a coarse stone. Mine on the other hand had a shallow bevel and I had polished it almost to a mirror polish. He could, admittedly hold a piece of paper up and slice cleanly through it with one slash whereas I could not. I could shave the hair from my arm though. Which would you say was the sharpest?

 

Well, on the one hand it depends upon what you want your knife for, if you are slicing meat all day for instance you might opt for a coarse bevel and coarse sharpen so that your knife will slice (basically saw) through the meat. The knife will effectively be a serrated knife but will have the kind of serrations that you may not be able to easily see, (micro-serrations). This kind of edge though will not shave the hair off your arm and will not take a thin sliver of wood from a carving. The knife I had sharpened was intended for carving wood, the edge was extremely fine and was intended for easily "pushing" through stuff rather than "slicing" or sawing through stuff.

 

A razor sharp but highly polished edge will not necessarily be the best knife for cutting tomatoes for instance. But it would give a fabulous finish to a piece of wood with each cut.

 

I'm often guilty of taking my knife sharpening too far and ending up with a razor edge on things like kitchen knives, which don't need that level of sharp. Also, most,(non-Japanese) kitchen knives tend to be made rather softer than a knife you would carve with. This is a bit of a trade off between the rust inhibiting qualities of stainless steel and the fact that knives in constant use lose their edge and require frequent sharpening which, if you are working in a busy kitchen you may not have much time for and so would want to be easy and quick. So professional kitchen knives tend to be highly rust resistant and slightly softer than other tools.

 

So, in terms of the age old question of what is sharp? My answer is. It depends what you want it for….

 

In my case I want an edge that is extremely shallow, mirror polished and will push through the things I use a knife for, wood usually. I do not work in an abattoir and I do not ever use my knives as screwdrivers or crow-bars. If you want a crow-bar, buy a crow-bar. For my knives I like a really hard steel for the edge and because I don't use them to lever anything open I don't need to worry about them being a bit brittle. The knives I make for myself are therefore, hardened but not tempered. For most cutlers that would be sacrilege, look up the purpose of tempering and you'll understand why.

 

Now that we have got past that question we come to the question of blade profiles. There are probably five basic blade profiles in general use.

 

Secondary bevel - sometimes called sabre grind or flat ground

Hollow ground

Scandinavian (Scandi) grind

Chisel grind

Convex grind

 

Flat grind and Hollow ground knives can be considered together because they both have a tapered section and then a secondary bevel. Most pocket knives, kitchen knives in the UK have tended to fall into this category. Typically the blade will either taper for it's entire width and then have a secondary bevel close to the edge or will be flat for about half it's width before tapering more sharply and then ending with a secondary bevel.

 

This style of edge profile has been used very widely in the past because it gives a very strong and highly durable edge with a fairly steep angle and plenty of metal behind the edge. Also an advantage of this profile is that when you sharpen the edge you are removing much less metal than with some others. One of it's biggest downsides though is that you need to be fairly precise about the angle when sharpening.

 

Hollow ground edges have been used for situations where the blade would need to have a reduced surface area and therefore less friction when cutting. With all other grind profiles the entire face of the knife will drag against the material being cut and the consequent friction will cause the knife to require more force to cut. This incidentally is another factor in how coarse the sharpening is, the coarser the hone, the less friction, the smoother the hone, the more drag due to friction. Some Japanese and cured meat slicing knives also use a principle of having several dished depressions in the blade behind the cutting edge to further reduce the friction coefficient.

 

Interestingly enough most of these grinds will still use the same basic blade geometry (angle of bevel), standard wisdom on this is around 22.5 degrees. My own preferences are for a shallower angle of around 18 degrees but there is nothing cast in stone about that. It means that my knife edges are sharper but more delicate than most others. Again I say, if you want a lever buy a crow-bar, not a knife, knives are intended for cutting not for opening tins or screwing in screws.

 

I sometimes find that far too much emphasis is placed on what the angle of the bevel is, basically if it cuts the way you want it and keeps it's edge then you've got the right angle for you….

 

Scandinavian grind or to use the slang "Scandi" has a much wider bevel, typically Scandinavian grind knives which have been made very popular by the bushcraft fraternity will have a flat blade with little or no taper and then a very deep bevel. There is no secondary bevel and sharpening/honing involves laying the bevel flat on a stone. This method is reputed to offer an easy way to ensure you get the correct blade geometry but does mean that you are removing an awful lot of metal to sharpen your knife. Incidentally I also have some reservations about how easy it is to maintain the wide bevel absolutely flat on the stone the whole time, especially when sharpening a curved blade. For a quick touch-up to the edge while in the field I doubt whether this is actually possible. I therefore suspect that most scandi grind knives will in practice have a very small micro-bevel or they will have a slightly convex profile.

 

Scandinavian grind knives are very popular for whittling and woodcarving as the edge will provide an extremely sharp and quite shallow cut. The usual knife of choice for whittlers and spoon-carvers is the Sloyd style of knife. These are usually scandi grind with a laminated steel blade providing an exceptionally hard steel as a core. They can also be obtained very inexpensively thus making them very popular.

 

Chisel Grind is a style which is extremely common in Japanese knives with the Kiridashi style being the most common for smaller knives. Also extensively used in Japanese kitchen knives