Dear OK,
I remember as a child when the Jewish knife sharpener would come door to door to sharpen knives around the neighborhood. Now, my only option is to send my knives to a professional sharpening service. Is it permissible to get a knife sharpened by a professional knife-sharpener who also sharpens non-kosher knives?
Rabbi Hanoka responds:
It is permissible to get a kosher knife sharpened by a professional knife-sharpener, even if he also sharpens non-kosher knives. Even though the friction from sharpening causes a lot of heat buildup, the heat is meant to take away something from the knife in order to make it sharper, so it does not pose a kashrus problem.
Please note, an identifying sign is recommended to insure that your knife is returned to you.