Good question!
In my mind, and I am a traditional knife user: (that means that I whittle in wet fresh wood, butcher fresh meat, butcher fish and so on. I very seldome slice cardboard, nylon, paper, plastic and ao on as city people do).
A knife shall only be as sharp it need to be for its purpouse, not sharper, or duller, then that.
If i shall whittle in soft wood I use flat edges in 18-19 degrees and they work dine and hold dor the job. If I keep the knife and start ro whittle in hard wood the edge need more power - and that destroy the edge fast = the edge get dull fast.
Har wood need higher edge angle, oak for example need 23-24 degree edges to hold.
Low edge angles has less material in and behind the edge = they are more sensitive and you cannot use hard force when using them. Steep edges has more material in the edge = they are not sensitive, you can use more force and use the edge in harder materials.
Two flat and smooth surfaces that meet eachother in a low angle = sharp.
100% flat can only be made with the help of a good sharpening tool.
Smoothness = depends of your choice of sharpeners and hiw fine they are.
Meet eachother =up to you to control
Low angle = the knife edge hold 40 degerees or less totally.
In Scandinavia our traditional edges are around 20 degrees total. In US edges often holds 40 degrees total. A Scandinavian axe holds around 35 degrees.
As you can se, edge angles varius a lot depending on where theyvare used in the world - and to what.
Scandinavian traditional knife knowledge says that you only slice with a knife = we never batoon or chop with knifes - unless the knife is a real chopper = a knife special made for chopping.
In US people chop with their knifes = the edge must be steeper. That also means that the edge penetration skill is not so good compare to a Scandi knife on 20 degrees total.
The knifes purpouse:
If I have a good perfect working hunting knife and I make the edge hair whittling sharp I have change the knifes purpouse from hunting knife to a razor - and I can not use this razor as a hunting knife any more, it is to sharp. It will slice hole in the hud when I skin my game and it will slice hole in the thin hins that protect the meat from flys and other bugs and they can lay eggs in the meat.
My outdoor knifes have 3 degrees convex sphere and the cutting edge holds 26 degrees total. I carry one normal knife with around 10 cm long Scandi blade, and one chopper with 20 cm long blade. During 50 years in the mountains and in the forests they work perfect for me and solve all my problems. During the winter I also have a axe with me.
Thomas
