Performing heavy work on Fridays

Hi,

One may not engage in heavy labor on Friday afternoon, lest this prevent him from preparing for Shabbat. We are taught that one who does so will ultimately lose whatever profit he made from that work.

However, one may do work, even heavy work, as part of his preparations for Shabbat - whether for himself, or on behalf of someone else (assuming he is doing it for free).

(Code of Jewish Law Orach Chaim 251:1-2)

Have a great day,
Mordechai