  HUGE drill bit.
This is one big drill bit, about 3" diameter and 15" long, before it broke. Broke, you say? Yes, I was using it, dangling on the end of a thin steel cable, as a counterweight to balance a rocket fuel tank on my rotation photography turntable (see next iron sample). The cable broke as I was adjusting it, dropping this bit about four feet to the concrete floor, where it snapped neatly in two. Yes, it landed about an inch and a half from my toes, and no, I was not wearing shoes.
I would like to say in my defense that I did consider at all times the possibility that it might fall, and I was making an effort to keep my bare feet out from under its likely path to the ground. I like to think that's why it missed my toes.
The fact that it broke in half was a complete surprise. This is a drill bit meant to cut through steel, and it's going to just shatter like that? But actually this is not so surprising. In order to cut through steel a bit has to be extremely hard, and the harder you make steel, the more brittle it becomes. Apprentice machinists are taught to treat the most expensive bits carefully, not just because they are expensive, but because they are also more likely to be damaged by just this kind of fall. Hardness is not the same thing as toughness.
Fortunately it's no great loss, I got this bit in a box of scrap and random stuff at the closing out auction of a large industrial manufacturing concern. It was no use to me (like I have a boring machine that big?). In fact, I wasn't even going to list it as a sample until it broke, revealing the fresh, cleanly broken surface inside. The fall greatly improved its value as an element sample. The fine grain (visible most easily in the 72-frame 3D rotation) on the broken surface shows this to be high-grade tool steel.
Source: Theodore Gray
Contributor: Theodore Gray
Acquired: 9 May, 2007
Text Updated: 29 January, 2009
Price: $1
Size: 8"
Purity: >95%
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