What Is the Edge Angle?

How do you decide the sharpening angle?

This was the first question when I started learning sharpening. Many of my customers asked me same. I checked tons of same question on the google search.

Similar question is that what is the angle of the edge. 

15 degree? 13 degree? There are many opinions in Google search. 

I worked in electric part manufacturing field before came in knife industry. Electronic components have details specification about size, thickness, length, width. Good quality means actual size is within the criteria of specification.

How do you check the shape of the knife in quality control? I asked it every workshops I visited in my hometown.

All the answers are same. Craftsmen check it by their sense. They don't have any specification and tools to measure it. Craftsman touch and see, then decide if it's good or not. There is no clear specification, no documentation. 

I learned knife sharpening and basic making process in the training center. I asked same question to the old teacher there. Teacher craftsman said "You are stupid. How can you measure it. Knife is not mechanic part."

After finish the training and start sharpening service, I realized that the knife has 3 dimensional curved surface. We don't have the way to measure it.

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Conclusion:

Conclusion: The shape of knives is 3 dimensional curve. Edge cannot be described by angle. There is no way to describe by numbers. It's made by human sense and experience.