Daf Yomi - Beitza 28 - Sharpening the Knife

The Mishna rules that one may not sharpen the shechita knife on Yom Tov in the manner in which he would do it during the weekday. One is permitted to prepare foods by performing a melocha providing that it is with the food directly.

The Ran in the first perek stated that one is permitted to carry the shechita knife in a public domain on Yom Tov since this is regarded as preparing the food and not just a preliminary phase. The Avnei Neizer (O"C 410) explains that it is considered ochel nefesh because the person is bringing the knife closer to the food.

Rav Shlomo Zalman comments that this is understandable only if the knife is already usable to perform the shechita; however where the knife would still require sharpening, then it cannot be considered ochel nefesh and that is why the Mishna prohibits sharpening the knife.