Q. Hi, I have a question.
Am I allowed to fold up a box on Shabbos? For example, if I finish a box of grape juice can I open up the other side to fold the box? Is that OK? I'm really not doing much (other than ripping a bit of tape).
On a similar note, when I throw out an aluminium foil tin, can I bend the sides in first?
A. Horav Shlomo Miller's Shlit”a opinion is that it is prohibited. This applies even when the ripping and disposal may be needed for this Shabbos in order to keep the abode clean and neat, and it is not done for readying and preparing for after Shabbos. It is forbidden, because you can not destroy utensils during Shabbos. (Mekalkel is exempt of punishment but Rabbinically prohibited, Baba Kama 86a).
If no ripping or tearing is involved, you are allowed to bend the sides of a cardboard or aluminium container, that can easily be restored to the original condition, when needed for that Shabbos.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a