Re: Chosera Angles versus Diamond Angles?

[wickededge]

Not sure that the gist of the tables is understood after seeing Tom’s comments.

The calculated angle in the tables is the actual angle you wll get when the set angle on the crossbar is as indicated
in the tables. Thus for the half width of the hone, r=.6 inch,
the angle set on the crossbar is about right only if the blade extension above the clamp is about 1/2 inch. The higher the blade extension the more the true angle deviates from the set angle. For the extreme case of 2 inch blade extension and a set angle of 22 deg (h= 2 inch, r=0.6)the actual angle will be about 16.7 deg for example. For the thicker hones,like the Shaptons this same setting yields a true angle of (r=0.8 inch, h=2inch ) 14.9 deg. you should be able to roughly confirm this using the angle cube (the accuracy of the angle cube setup is such that its difficult to get better than 1 deg resolution in my experience. NOTE: ITS MY SETUP, NOT THE ANGLE CUBE,THATCAUSES THIS 1 DEG INNACCURACY)

you can see the effect of stone dishing by recognizing that for any fixed set angle on the crossbar the true angle will be more for the thinner section of the hone. In effect a dished stone will convex the edge slightly. The effect is really too small to capture in the tables since it would only be a difference of r=0.800 inch at the end of the hone and r=0.795 inch at the lowest dished point. the measurements required to construct the tables are certainly not accurate enough to do this.

Conclusion: thicker stones(r> .6 inch) give less of an angle than is set on the crossbar. Hence unless you increase the set angle you will not reach the edge with the thicker stones on an knife initially sharpened with the thin stones. The tables are intended to give you an indication of how large the variation is.

Again keep in mind that the tables are for the stones centered on the clamp,with no swing forward or backward.

Correct. FWIW, the angle remains the same along the straight portion of the blade and only changes with varying heights of blade or curvature. It’s most noticeable along the curve of the belly because the stone is rotating on the rod as it sweeps through the curve and constantly entering a new plane of contact. Had we gone with square guide rods and square holes in the handles, that effect would be eliminated but we’d lose some of the flexibility with different knife designs.

-Clay