Convex sharpening

J

Joe_Lane

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Jul 15, 2014
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I've been reading this guide on convex sharpening http://brkca.com/convex.htm. Everything makes sense except for where it says do NOT lift the blade when you get to the belly. It says to turn the knife and follow the curve as clearly shown in the pictures. Maybe there is something I don't understand but i'm not finding it physically possible to do so. :confused:
 
Last edited:
The link has some extra characters in it. I found the article here:

http://www.brkca.com/convex.htm


The geometry of the edge requires that you lift the handle when you go around the curve near the tip. Assuming you have a knife where the straight part of the edge is parallel to the axis of the handle, you lay the blade on the sandpaper and raise the spine which rotates the knife around the axis of the handle. If you had started nearer to the point by laying the blade on the sandpaper and rotating the blade to do the same as raising the spine and lowering the edge and you will find that you are raising the handle slightly. It is probably intuitive what needs to happen- if you start by raising the spine you will create an angle between the sandpaper and the edge. As you work your way around the curve you maintain this same angle with the part of the edge that contacts the sandpaper.
 
Joe_Lane said:
I've been reading this guide on convex sharpening http://brkca.com/convex.htm. Everything makes sense except for where it says do NOT lift the blade when you get to the belly. It says to turn the knife and follow the curve as clearly shown in the pictures. Maybe there is something I don't understand but i'm not finding it physically possible to do so. :confused:
Click to expand...

This really perplexed me when I started sharpening convex grind knives. It is physically impossible (that I can see) to sharpen the tip/belly without lifting the handle - assuming you are sharpening from handle to tip. I don't quite get that part of the directions either.
 
ecallahan said:
This really perplexed me when I started sharpening convex grind knives. It is physically impossible (that I can see) to sharpen the tip/belly without lifting the handle - assuming you are sharpening from handle to tip. I don't quite get that part of the directions either.
Click to expand...

It's not impossible. But not lifting the handle means the existing factory grind in the belly & tip might have to be thinned a lot (a LOT), before apexing the edge in those portions. This is the only difference made, in not lifting the handle. If wanting to maintain the existing grind angle on most knives, the handle will have to be lifted for the belly & tip, due to the thicker grind in those portions and the resulting wider (more obtuse) edge angle.

I mention the above, because I've deliberately thinned the tips on most of my knives by doing just as those instructions recommend (keeping the handle low, and just turning the knife instead). It usually takes a LONG time to fully apex in doing so, but the (much) better piercing characteristic of the thinner tip is worth the work, in my view.


David
 
Turning the knife so that the edge is always perpendicular to the abrasive does lift the handle relative to the surface. Imagine cutting something with a knife with a pronounced belly. To utilize the whole cutting edge you would lift the handle, right? But your are just following the edge shape. Same thing, just the angle is not 90 degrees but your sharpening angle, 15 degrees for instance.

We will have to make a video about this issue since it seems to cause a lot of confusion.
 
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