Question on filing a concave edge

Alarion

Alarion

Joined
Nov 26, 2001
Messages
1,375
I'm building a knife with an edge which follows a pattern similar to a kukri.
A fat "belly" and a concave part near the ricasso.
The concave part is giving me hell.
I can't keep decent sharp corners between the bevels and the flats of the blade. No way.
And I'm filing the annealed steel.
When the blade will be heat treated and I'll have to sand the hardened steel things are going to be even worse...
Can anybody help me here?
 
Have you tried a file with a convex face? You'd have to be careful not to work in one spot, since it would cut a groove, but it would keep the edges of the file from tearing things up.
 
Measure in from the edge to be, the width of bevel you desire, and draw a line following the curve. Put tape along this line (cover the flat area, the tape will bunch up a little on the curves). Clamp the knife horizontally and draw file it, or file the regular way, just stay off the tape. Initially you can flat file, and then convex file as you progress.
 
Alarion,
In re-reading your initial post I realize I answered the part about keeping an even transition between the flat and bevel, so the bevel looks constant or even. I'm not sure what you mean by the concave part, unless you are talking about the change from the wide part of the bevel to the narrow cutting edge. The import kukri I have is convex ground, which keeps the bevel thick almost all the way to the cutting edge. If you wanted it hollow ground, I suppose a convex file could be used, again with the tape guideline. It would be easiest with a wheel on a belt grinder.
I'm also wondering if you aren't referring to just the ricasso or plunge area and not the whole blade. Some makers clamp a piece of steel (preferably hardened) in the ricasso area as a guide for the file or grinding wheel.
 
I was sort of guessing about that too. You can't do a hollow grind with a file. It has to be done on a contact wheel.

I was assuming that you had trouble filing the blade inside the recurve. Which would be tough since only the edges of the file would make contact and it wouldn't cut very well, just gouge out thin lines. Whereas the convex faced file would make contact in the middle of the file and would cut normally.
Same idea as sharpening a recurve edge. You need a narrow stone or croc stic, as opposed to a wide bench stone.

Are we on the same page?
 
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