Thinning layered Japanese knife

[Jgushue]

Hi, the blade has been sharpened in the past so that the two soft outer layers are now at the cutting edge. When new, these layers were 6-8mm up from the cutting edge.  How do I pull these layers back up away from the hard edge. I have a t-8. Joe

[tgbto]

If your blade is still usable, shape-wise, after having lost 8 mm of height, then two things :
- you don't *have to* remove these layers if the blade is still thin enough, they will sharpen easily and the cutting will still be done by the hard steel
- if the blade is significantly thicker at this point, you have to thin it exactly the same way you'd do with any knife : grind it at a shallow angle till you have a "zero edge" (little to no bevel due to the thinness of the blade) then sharpen it at your usual angle.

How shallow of an angle you want is a matter for discussion. As a rule, you want it significantly below your sharpening angle, but still significantly higher than the base angle of the blade from spine to original edge. So if, say, your base angle is 1dps, and your usual sharpening angle is 15dps, 3 to 4 dps is a safe bet.

Your base angle is arcsin(spine_thickness/(2*original_blade_height)). Also, please note that this will take time on a Tormek, and must not be rushed.