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.