Lathe Cutting Tool for O-ring Grooves (and trepanning)

[mklotz]

It's worse than that. Many ancient societies, not yet out of the stone age, were trepanning people to release evil spirits. They were using flint knives! We know that this is true because skulls have been found with nice round holes and new bone grown at the circumference of the holes, proving that the patient survived the operation at least for a while. The holes are far too big to have been made by a survivable blow from a weapon. Any weapon large enough to make the hole would have penetrated too far into the brain to be survivable.

Even today, some nutbars think the procedure has beneficial effects and do it when not needed surgically. Full story here...

https://www.damninteresting.com/the-...n-trepanation/

If you're interested in trying this exciting form of self-medication, an antique trepanning brace is available...

https://ahp.apps01.yorku.ca/?p=268

If that's too slow, a Starrett hole saw in a Milwaukee cordless drill will do the job just fine.