In a recent issue of the MachinePix newsletter, Kane Hsieh interviewed Dr. Steve Gass, the inventor of the SawStop, the table saw that automatically stops cutting when it detects human skin (therefore saving fingers and hands from being cut off). Before we get to that, you've probably seen the company's hot dog demo but if you haven't, check out these super slow-motion clips of the SawStop blades stopping in a matter of milliseconds after making contact:
The minuscule amount of damage to the hot dog is mind-blowing. Where did this demo idea come from? From the interview:
What was the first thing? It was probably a stationary blade with me just touching it with my finger. Once we started spinning the blade, I wasn't too eager to do that test with my finger, so we just thought 'what do we have that's sort of finger like with similar electrical properties' — hot dogs are similar, and I had one in the fridge, so I grabbed one and ran it into the blade. Sure enough, it worked.
There was a point where we had to know a hotdog was a good surrogate for a finger. You can imagine, we could do this demo at trade shows with a hot dog, but there's always a smart-ass that says they don't care about hot dogs, and wanted to see it with a finger. So before the first trade show I had to test it with my actual finger. Thankfully it worked!
And because what the saw is detecting is "the capacitance of the human body", you have to be holding the hot dog in order for the demo to work.
The whole interview is worth a read — like this bit about why big tool companies were not interested in licensing this feature: because they aren't liable for the injuries caused by their products:
The fundamental question came down to economics. Almost a societal economic structure question. The CPSC says table saws result in about $4B in damage annually. The market for table saws is about $200-400M. This is a product that does almost 10x in damage as the market size. There's a disconnect — these costs are borne by individuals, the medical system, workers comp — and not paid by the power tools company. Because of that, there's not that much incentive to improve the safety of these tools. Societally if there was an opportunity to spend $5 to save $10, we'd want to do that. But in this chain there's a break in people that can make those changes and people that are affected, so it's not done.