Couldn't find the chapter 118 post and can't be bothered to make one, so this'll do as they go hand in hand as Hild's backstory.
So far this has been really well researched, but was Hild isekai'd from the future? Sawmills! Whilst the Romans and other ancient societies had them, Vikings didn't even hand saw their wood! https://www.hurstwic.org/history/articles/manufacturing/text/viking_woodworking_riving.htm
Ancient saw mills also used a larger version of saw blade which the mechanism pulled up and down.
The circular blade and the ball bearing weren't invented until the late 18th century!
EDIT:
LOL, just read the afterword. Yukimura got the idea of the sawmill from an anime: https://myanimelist.net/anime/2836/Chiisana_Viking_Vickie?cat=anime
I vaguely remember watching some episodes of this as a kid!