I recently built an attachment for my grinder: a setup for a 10” diameter contact wheel. This was a huge step up in my arsenal: hollow ground knives initiate a cut at an insanely thin angle, for maximum efficiency on the initial cut. The only drawback is that the angle becomes increasingly obtuse as you continue the cut, making it best suited to cutting thick objects.
Turns out, that’s not the only drawback.
Dangers of super thin hollow grinds
The problem was, I didn’t do my homework on hollow grinds. I approached a few knives just like I would a full flat grind: grind to “zero”, thinner than any hollow grind I had done before. This means grind away until you’ve eliminated the flat surface on the edge (like establishing the blade edge in sharpening, as covered last week). This works well on a flat grind because the material thickness increases relatively quickly, but for a hollow grind, you’re left with less than a millimeter thickness for nearly 1/16” or so.
This didn’t bode well for heavy performance. The edge did not hold up to the brass rod test: it punctured a bit, then crinkled... and finally chipped.
I think my heart did likewise.
It could have been a heat treat issue, but after testing some other factors, I believe it was geometry. The blade was simply too thin to hold up to any serious use. In fact, it’s likely that I brought the grind too far back, increasing the amount of super thin steel. This was a heartbreaking realization; four knives, forged, heat treated, ground, and wrapped, all in the dump heap.
That said, I learned. Any and every failure shows me how I went wrong, and the concept, attached to the “pain” of how I learned it, makes it far more memorable.