Clearly, making big gears is a specialized job. And this factory somewhere in Asia seems to be doing only that. They cast them in a slightly larger shape, and then machine them on huge lathes and other high-powered tools to get them to within specifications. you might think there is child labor going on here when you see the video, but I'd bet my reputation on it that the kid is in an apprenticeship, probably learning the job like his father before him.
It is intriguing to see how the knowhow of these people has shaped the way they do their job, and the way how each of them has his or her own specialty.