Secondary edge

[Mrd831]

Hello could someone explain why some blade Smith's put a secondary edge on convex knives instead of a full convex thanks

 

[tyyreaun]

Probably for edge strength. Depending on what apex angle you'd end up getting with a convex zero grind, the edge might end up being very weak, and prone to chipping or rolling.

 

[Mrd831]

Thank you for your response. I have posed this question on other forums and in person. most answers seem to agree with you unfortunately I can't seem to grasp this concept I feel a full convex zero grind would be stronger and also why bother with the convex if it's not a true convex I feel like I have learning disability on this one lol I just can't get it !!!!!!!!

 

[tyyreaun]

I feel a full convex zero grind would be stronger

Why would it be?

Say you grind a knife to a convex zero grind - it ends up with a certain edge angle, based on the overall geometry. If you then sharpen it to add a secondary bevel, you're increasing the apex angle - you can't decrease it without regrinding the entire knife. With a more obtuse apex angle, you have more material at the edge, which by definition would be tougher, at the cost of some cutting ability.

 

[Richard338]

I went full convex on a competition style chopper. It cuts great and is strong. This is pretty common. The reason you probably see a small secondary added is that then just about anyone can sharpen it. With full convex, only the maker is set up to sharpen easily. People do hand polish katanas to a zero convex edge, but it is not for amateurs.

 

[USMCPOP]

I learned to make convex edges on my machetes when I was in Thailand 40+ years ago. Used a soft stone or a harder one that was worn sway-backed. It was easy, just back-and-forth. Rub it near flat, start raising it when you get tired of all the effort, then raise it again when you get to an edge. Kind of like slack-belt grinding. Convex is just a general profile, not an exact geometry in my opinion. It's like a catenary arch with a bit of Gothic point to it.