Is combing a wig permitted on Shabbos?
We must differentiate between “setting” a wig, and conventional combing. Setting a wig includes the initial setting and the rearranging of a tangled wig. This involves an issur of tikun manah – repairing a k’li ,1 and an issur of extracting hair.2 Since the wig could not be worn in its present state, it is considered impaired, and rearranging it is equivalent to “fixing” it.
Regular day-to-day combing of a wig is permitted, and one should use a type of brush or comb that will not necessarily remove hairs from the wig.
May I slice a tomato with a shechita knife?
A shechita knife is one of the items that are muktze machmas chisaron kis, which means that it belongs in the class of items that are muktze because of their value. The wide-ranging group of muktze items is subdivided into several categories, which sometimes differ from one another with regards to their laws. As we go along, we will B”H learn the specific laws for each group.
Items used for purposes that are forbidden to do on Shabbos, and one is very particular about using them for anything but their intended purpose due to their value, are in the category of chisaron kis.
This would include a shechita knife. Besides being an expensive knife, a shochet is extremely careful that his knife does not get nicked or dented. He therefore places it in a secure place out of harm’s way.
The halacha is that one may not use an item which is muktze machmas chisaron kis for any other use, nor move it from a space one needs to use that it is occupying. The halacha terms it l’tsorech gufo um’komo. 3
One is therefore forbidden to use a shechita knife to slice a tomato, because this category of muktze is totally forbidden to use or move on Shabbos.
What if I change my mind on Shabbos and from now on want to use the shechita knife as a regular kitchen knife?
The Mishna Berura 4 quotes the Magen Avraham saying that even if the k’li broke on Shabbos, thereby causing the owner of the k’li to set it aside for another use, since it was muktze when Shabbos came in, it remains muktze for the duration of the Shabbos. Therefore, even if one changed his mind and wants to use the k’li from now on for a use that would not render it muktze, he may do so for the next Shabbos, but as far as this Shabbos is concerned, the k’li remains muktze.
There are many more muktze items under this category of chisaron kis, which can be found in the seforim on Hilchos Shabbos.
Is one permitted to move a heavy cupboard on Shabbos?
Even though a heavy cupboard is hardly ever moved, nevertheless it is not branded as a muktze item.5 If however, the cupboard is not moved for fear that it would get damaged, it is then considered as part of the category of a chisaron kis. 6 This is because the definition of a chisaron kis is that one is careful not to do anything with the k’li that might damage or spoil it. This would also apply to a fragile cupboard.
Is the sign “v’tein tal umatar” muktze on Shabbos?
Even though chisaron kis is defined as a muktze where items are set aside for safekeeping, this would not apply to a sign of “v’tein tal umatar livrachah“. This is because this particular notice is not put there for safekeeping, rather so as to enable everyone to see it. Therefore, the sign may be changed on the first day of Pesach.
 Ktzos HaShulchan 143, footnote 6.
 Sh’miras Shabbos Kehilchasa 14:26, footnote 123 and vol.3 footnote ibid.
 Gufo = its body, in other words for use of the actual k’li. M’komo = its place that it is occupying.
 Simon 308:35, towards the end.
 Simon 308:2.
 M”B 308:8.