The 1916 poem was based on a true story about a boy that Robert knew, who died in 1910. They did have circular-saw like machines in 1910 that were popular for cutting firewood, according to my wiki dive.

It’s a fixed buzzsaw. One might be confused by the “leaped at his hand”, but Frost says in reality that “he must have given the hand”.

Basically, his sister called him to supper, which apparently distracted the boy enough that he accidentally stuck his hand in the blade.

A buzzsaw is in essence a large version of a table saw, and table saws eat many fingers and thumbs every year. Now imagine that the table saw blade is four feet tall.