Grenadier,
Excellent video!
What a lot of people don't realize is that there was a whole industry built up around the making of files.
Generically they were referred to as "file smiths". But, the cutting of the teeth in a file after the smith was finished was a very special trade known as file "cutters".
Each and ever one of those teeth you see in a file was originally cut, or perhaps I should say upset by hand.
All of this Smithing/Hammer work is, of course, done well before the hardening of the steel these are made from.
Thank you so much for posting...
My best,
Blair