What are the advantages and disadvantages of an acute edge 30 degrees or less vs an edge that is more obtuse (40 and up)?. Do blades with acute edges require frequent sharpening?. Lastly does the hardness of the steel matter in what type of edge it should have i.e are softer steels better off with more obtuse edges than harder steels or should it be the other way around??
Fez
What are the advantages and disadvantages of an acute edge 30 degrees or less vs an edge that is more obtuse (40 and up)?
That is really up to the user. Only you can really answer that question (or discern if there is any noticeable difference). Personally, I feel that the more acute the angle is, the more that the edge wants to cut or "bite". Additionally, I have done some demonstrations showing the reduced pressure needed at the handle to make the same push cut with a more acute angle (I proved it to me, it is up to you to prove it to you...then decide if it is worth the effort).
Do blades with acute edges require frequent sharpening?
Generally speaking, yes. All else equal, a more acute angle has less metal on the shoulders of the cutting edge to support it. There is a balance for every user between how acute the angle needs to be and how durable you need the edge to be.
Regarding steel. Hardness is one component. Metallurgy is another. You can (and others have) write quite a bit on the topic.
Another consideration is the overall geometry of the blade. As you grind the blade thinner behind the edge bevel, the angle of the bevel becomes less important.
A knife blade is really basically a ramp or wedge. Generally speaking the angle of the ramp is going to dictate (to some degree) how hard it is to push something up that ramp. The edge bevel is the angle of the first ramp, but if that ramp is REALLY short you then start considering the effective angle of the rest of the blade...and the surface finish (now we are talking about friction as you push something up that ramp). It should be said that the depth of the cut will determine how much of this blade geometry will come into play...if you are cutting or whittling hair, you are really only considering the leading edge of the blade. By contrast if you are trying to cut a several inch diameter barge rope, you are going to be experiencing more of the blade's geometry during the cut.
Of coarse you also must consider what sort of cutting you are doing (chopping, push cutting, slicing, etc.)
Welcome to some deep discussion regarding one of the simplest tools known to man (next to the hammer).
