Q. Can you use a single sharpener to sharpen knives fleishig and milchig? How about giving them to sharpen to a non-Jewish company?
A. On question 655 in regards to the use a metal or stone knife sharpener for fleshig and milchig knifes, and if they require tevilah, we wrote: “Poskim permit using the same sharpening stone or steel for meat and milk knifes and utensils even when used that day (Ben Yomo) and even if the sharpening creates enough heat that reaches the Yad Soledes temperature (about 45°C). However they should be clean, but could be slightly wet. (Shevet Hak’hosi Y.D. 192 – Moriah, year 16: Av: p. 88, quoting Horav Y. N. Karelitz Shlit”a – Ohel Yaakov 92: n. 72.) They (sharpeners) do not require immersion in a Mikva since they don’t come in contact directly with food.
Horav Shlomo Miller’s Shlit”a opinion is similar”
In regard to giving them to sharpen to a non-Jewish company, Hagolas Keilim (13: 260) quotes an opinion that does not allow giving knifes to a Gentile to sharpen out of concern that the sharpeners will have a residue from non-kosher meat or fats. However, he points out that, in our times, people regularly give knives to be sharpened when they are clean. Furthermore, he mentions that even in the time of the Rishonim, some Poskim were not concerned about this issue. For example, the Mordechai (Avoda Zara 833), discussing the danger of giving a knife to a non-Jew for sharpening, raises only the concern that the craftsman will use it for his own personal use, not that the sharpening itself is problematic.
Horav Shlomo Miller’s Shlit’a opinion is that when using a knife sharpening service, care must be taken to clean the knives properly before and after giving and receiving them. Also great precaution should be taken to mark properly the knives, so they will not be exchanged for others.
Rabbi a. Bartfeld as revised by Horav Shlomo Miller Shlit’a