sharping question

[Dr sharp]

From what i read its my understanding that if a blade is scary sharp, it doesnt hold up for that long versus if its just normal hair popin sharp. Is this due to the fact that the scary sharp angle in more steep? maybe some one could give us a quick lesson about sharping and which holds up longest. While im here i have another question ive always wondered...lets say a blade is hardened to 85 rockwell..well as long as you always cut things below 85 in hardness, then shouldnt it stay sharp for life. It seems to me when i knife dulls its because the sharp edge flattens out, but if you cut nothing but soft things, shouldnt it stay sharp for life....someone please enlighten me.

 

[Cliff Stamp]

Dr sharp :

if a blade is scary sharp, it doesnt hold up for that long versus if its just normal hair popin sharp.

This is a myth. With a given geometry, the sharper an edge the more durable. As the geometry is altered then so is the durability but this is more of an issue of cutting ability and not simply sharpness.

It would be correct to say in general that refining the cutting ability of a knife by reducing the edge geometry will cause a loss in durability, there are exceptions to this, but it is always a major consideration.

lets say a blade is hardened to 85 rockwell..well as long as you always cut things below 85 in hardness, then shouldnt it stay sharp for life.

No because you don't need to compress steel to make the edge go blunt. Edges can blunt by deformation by bending sideways which can be done by contact with a much softer object.

Consider sticking a Senebza one inch deep into a piece of wood and snapping the blade hard sideways - what will happen? The point will break off even though the wood is much softer than the blade, same thing with edges.

Blunting can also be caused by overheating, fracture both impact and fatigue and corrosion. Adhesive wear can also happen with softer materials but it usually isn't a large issue with knives.

-Cliff