concave secondary bevel - need help or how to discussion

A

AJH_Knives

Well-Known Member
Looking for some input on had to achieve a concave secondary bevel. is this the trick where you put felt on the platen and grind? also in my primary bevel is at 10* what should the secondary one be at?

thanks for the help guys

Aaron
 
Primary bevels are generally what they end up when you finish grinding the bevel to the spine or where ever you want to end them. Secondary bevels depend to some extent on the usage of the knife. A heavy chopper needs a courser secondary bevel and a caping knife would need a finer bevel. Generally you are aiming for 20-25°.

If I were to try to put a concave, aka hollow, grind on a blade I would use the drive where to achieve this. For a convex edge I would use a slack belt.

Doug
 
Its not so much the primary grind angle that dictates the edge bevel angle, its the overall geometry of the blade itself. A 10 degree inclusive grind on a knife that is 1/4 inch thick at the spine is not the same as the same grind on an 1/8 inch thick blade. Next is how close to zero the bevel is taken. A zero ground set of matching bevels on that 1/4 inch thick blade does not pose the same possibilities as does the zero ground bevel on the 1/8 inch thick blade. Selecting the correct edge bevel for a blade must take into consideration the job to be done for sure, but its the geometry that dictates what level of sharpness and how the edge functions during cutting. Grinding a "concave" secondary edge seems a contradiction in that the only place it would improve the cutting ability of a blade would be on a blade used as a camp tool; but in that situation its not keenness that is called for, its having a durable edge. If working on a blade where slicing ability or keenness is the goal; a change in geometry would seem a better solution than grinding the secondary bevel into a concave shape.
 
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