Machine holds/clamps

Why is it that I see so and tool hold or bar stock holds in machinery use claps likes this for cylindrical stock or tools? To me it just seems like when milling metal the forces are extreme but it seems very common to use a clamping style like this, which to me seems like it be very easy for it to come loose! For reference he was milling a 10 degree shaft at the end for a bearing



But just a curiosity

Judging by the picture, he put the round stock in at lathe tool holder. That would assume that he put the cutting attachment in the headstock of the lathe. The cutting forces aren’t too bad, although it would be an interrupted cut.

Not the way I would have done it though.

Me personally I would have used a 5C collet block in the Kurt vise with angle blocks & a boring bar in the head.

Wow pretty spot on from 2 very vague pics but my question being why is that the what seems to be tried and true way to clamp lathe tools, cause in some jobs that cylindrical tools rod can but in. Forces on several axis so how does it not slip out and withstand all that form what looks to be a very hard thing(metal rod) to clamp down only having 180 degrees held onto