Cutting tablecloth on Shabbos
Question
We use reels of nylon tablecloth. Oftentimes we don’t cut enough pieces for Shabbos. Is it permissible to cut it on Shabbos “in an irregular way” (be-shinui)? Thank you
Answer
It’s appropriate to avoid this situation. You should always keep spare pieces of cut nylon tablecloths in the house. You can also buy pre-cut tablecloths [there are the six-packs and eight-packs of precut tablecloths; or you can just cut a few extra pieces yourselves and put them away in a drawer for the time of need]. If need be, you can also cover your table with several smaller pieces.
In case of great need, what you can do is to cut a piece far larger than what you need for your table, without measuring how much you’re cutting, and cut it with a knife be-shinui (in an abnormal fashion); it has to be an “unprofessional” cut. You can be lenient and fold the extra length of the tablecloth underneath the cloth that covers the table.
Source
Biur Halacha, ch. 322