הִנֵּ֣ה שַׂמְתִּ֗יךְ לְמוֹרַג֙ חָר֣וּץ חָדָ֔שׁ בַּ֖עַל פִּֽיפִיּ֑וֹת תָּד֤וּשׁ הָרִים֙ וְתָדֹ֔ק וּגְבָע֖וֹת כַּמֹּ֥ץ תָּשִֽׂים׃
Behold, I make thee a new threshing-sledge Having sharp teeth; Thou shalt thresh the mountains, and beat them small, And shalt make the hills as chaff.
Rashi on Isaiah
a...grooved threshing sledge It is a heavy wooden implement made with many grooves, similar to the ironsmiths’ tool known as ‘lime’ in French, a file, and they drag it over the straw of the ears of grain and it cuts them until they become fine straw.
Ibn Ezra on Isaiah
למורג A threshing instrument. It is well known.22A.V., "Sharp." Comp. המוריגים threshing instruments (2 Sam. 24:22).
Rashi on Isaiah
new When it is new, before the points of its grooves are smoothed off, it cuts very much, but when it becomes old, the points of the grooves are smoothed off.