I failed at a hollow grind!

 


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

  From this angle the blade looks fantastic. Unfortunately, I just ground it too thin

From this angle the blade looks fantastic. Unfortunately, I just ground it too thin

 

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. 
 

Caleb Harris

I’ve always fooled around with tools and hardware, but I think my passion with blades started far back in my childhood: wooden swordfights with the neighborhood kids. I became the neighborhood “blacksmith”, using my grandfather’s tools to hammer little crossguards onto wooden sticks. I always tried to find the best scrap wood: lightest, strongest, trying to get the perfect length and shape for each “customer”. This started my passion with blades.
 
When I was ten years old, I joined a local rock and gem club, learning stonecutting and cabbing, and through that came to take silversmithing lessons from a local jeweler. It wasn’t until around the age of 13, that I turned my attention to bladesmithing, which has captured my heart. 
 My personal obsession with bladesmithing, as I’m sure you can relate, isn’t just the joy and passion of the making: the musical clang of the hammer on steel, the shower of sparks on the grinder, the whisk of the blade over the sharpening stone, but also of the fulfillment in creating something that is twofold: that of beauty, and that of function. It’s trying to make something that is as much an art piece, as a tool that you can trust your life with. That’s what caught my heart, and the pursuit of that perfect combination still drives me.