Someone mentioned to me that he saw that you wrote that putting a leaf in a table with a latch could be a deoraisa. What is the source for this. Is that called mehudak?
Halacha Talk
Assembling Portable Cribs and Adjusting Shtenders on Shabbos
by Rabbi Yirmiyohu Kaganoff

Question #1: I am having a lot of company for Shabbos and we have a small house. During Shabbos, I would like to remove the extra leaves from the table and set up the “porta crib,” and then in the morning fold up the crib and put the table leaves back. May I do this on Shabbos?

Question #2: I have an adjustable shtender that I usually leave at the same height. May I adjust it on Shabbos?

Question #3: The house is very crowded and stuffy because we are celebrating a kiddush. May I remove a door or a window to allow some additional ventilation? (I was asked this shaylah in Israel where doors and windows are hinged in a way that they are easily removable.) 

Question #4: May I remove the pieces of glass from a broken window on Shabbos?

Before discussing these shaylos, we need to explain the halachos of construction on Shabbos, and how they apply to movable items such as household furnishings and accessories.

CONSTRUCTION ON SHABBOS

Boneh, building or constructing, is one of the 39 melachos of Shabbos. Included in this melacha is performing any type of home repair or enhancement, even if only a minor repair (see Gemara Shabbos 102b). Thus, it is prohibited min haTorah to hammer a nail into a wall in order to hang a picture (Rashi, Eruvin 102a s.v. halacha). Similarly, one may not smooth the dirt floor of a house because this enhances the “structure” (Gemara Shabbos 73b).

Sosair, demolishing or razing, is also one of the 39 melachos, since Bnei Yisroel disassembled the mishkan whenever they moved it from place to place (Gemara Shabbos 31b). Therefore, any demolition of a building is prohibited min haTorah if the ultimate results are beneficial, such as razing part of a building in order to renovate it. 

If there are no benefits to the demolition, it is still prohibited midirabbanan. Thus, wrecking the house because someone is angry violates Shabbos only midirabbanan (according to most Rishonim) since there is no positive benefit from the destruction (Pri Megadim 314:11 in Eishel Avraham). It is prohibited min haTorah because of other reasons, such as bal tashchis (unnecessary destruction) and being bad for one’s middos (see Gemara Shabbos 105b).

We already have enough information to answer questions #3 and #4 above, regarding removing a window to ventilate the house and removing pieces of glass from a broken window. Both of these activities are prohibited min haTorah since they involve the melacha of sosair for positive results. Therefore, a Jew may not remove the window or the broken glass unless there is a life-threatening emergency. If the broken window is dangerous (but not life threatening), one can ask a non-Jew to remove the broken pieces of glass.

CONSTRUCTION OF MOVABLE ITEMS 

Do the melachos of boneh and sosair apply to movable items, keilim (sing., kli), as well, or only to buildings? In other words, does the Torah’s prohibition refer only to something connected to the ground, or does it include the construction of a movable item?

This question is disputed in the Gemara and by the Rishonim, who debate whether keilim are included in the prohibition of building and destroying on Shabbos (Gemara Beitzah 10a). There are three basic opinions:

1. Keilim are not included in the prohibition of boneh and sosair.

2. Keilim are totally included in the prohibition of boneh and sosair.

3. A compromise position in which total construction or destruction of a kli is prohibited min haTorah, but minor improvement is not (Tosafos Shabbos 74b and 102b). The halacha follows this opinion (Shulchan Aruch 314:1).

WHEN DOES BONEH APPLY TO KEILIM?

Assembling or improving a kli in a way that involves strength and skill constitutes boneh, and disassembling it involves sosair. Therefore, it is prohibited min haTorah to assemble a piece of furniture in a way that tightens the pieces since this involves strength and skill to do the job properly. Similarly, replacing the handle on a hoe or other appliance is prohibited min haTorah since it requires skill and strength to do the job properly (Gemara Shabbos 102b).

Assembling furniture without tightening the pieces is not prohibited min haTorah, but is prohibited midirabbanan out of concern that one might tighten them (Tosafos Shabbos 48a s.v. ha; Hagahos Ashri Shabbos 3:23). Therefore, one may not assemble a bed, crib, or table even without tightening the pieces (Kaf HaChayim 313:63).

Example:

One may not assemble a crib on Shabbos. Assembling it in a tight way is prohibited min haTorah, whereas assembling it without tightening the pieces is prohibited midirabbanan since one might assemble it tightly. (However, porta cribs which are meant to be assembled and taken apart, have a different halacha as I will explain shortly.)

FIXING A BROKEN APPLIANCE

Repairing a broken appliance on Shabbos follows the same guidelines as assembling. Therefore it is prohibited when the repair requires skill and strength even if one repairs it in a temporary way. 

Therefore, if the leg of a bed or table fell out, one may not reinsert it even temporarily out of concern that one might repair it permanently (Shulchan Aruch 313:8). In this instance, Chazal decreed that the bed or table itself becomes muktzah in order to ensure that someone does not repair it (Rama 308:16).

TWO EXCEPTIONS

There are two exceptions to this rabbinic prohibition, when one may assemble or repair an item in a non-permanent way. The first is on Yom Tov (Tosafos Beitzah 22a; Shulchan Aruch 519:2, Magen Avraham and Gr”a ad loc.). One may use a temporary repair to fix a furniture item for a Yom Tov need.

Example:

A leg fell off the table on Yom Tov. Repairing the table in a proper way is prohibited min haTorah, and therefore on Shabbos I may not even reinsert the leg into the table in a temporary way. However on Yom Tov, I may reinsert the leg without performing a proper repair if this is the most convenient table to use.

ANOTHER EXCEPTION

If the broken or disassembled item is usually repaired or assembled without strength or skill, I may repair it in a temporary fashion. Chazal did not forbid this since it is unlikely that it will cause any Torah violation (Gemara Shabbos 47b with Tosafos).

Example:

In the time of the Gemara there existed a type of bed called “a coppersmiths’ bed.” Apparently, it was common that coppersmiths traveled from place to place making their living as iterant repairmen, and took portable beds with them that they reassembled at each destination. May one assemble this bed on Shabbos or is it considered construction? The Gemara quotes a dispute on the subject. According to the Tanna who contends that keilim are totally included in the prohibition of boneh and sosair, one may not assemble these beds on Shabbos (Shabbos 47a).

However, the conclusion of the Gemara is that one may assemble these beds on Shabbos. That is because these beds were never assembled very tightly and therefore it is not considered boneh to construct them, nor does it qualify as a rabbinic prohibition. However, an appliance that was assembled very tightly would be prohibited to assemble even loosely since it might be tightened (Tosafos ad loc.).

Assembling the typical porta crib is similar to assembling a coppersmiths’ bed. Thus, one may assemble a porta crib on Shabbos and fold it up afterwards.

TABLE LEAVES

Inserting table leaves also does not require skill or strength and is therefore permitted on Shabbos. However, some tables have a clamp to tighten the table after inserting or removing the leaf. Since tightening this clamp might be prohibited min haTorah, one may not add or remove leaves from these tables on Shabbos. Even if one does not tighten the clamp, it is still forbidden out of concern that one might tighten it.

THE SCREW – AN INTERESTING INVENTION 

About three hundred and fifty years ago, the poskim began discussing appliances held together with screws. Around this time a drinking cup became available where the cup part screwed into a base. Does screwing this appliance together on Shabbos constitute boneh? 

The halacha question here is as follows: Although this cup does not require someone particularly strong or skilled to assemble and disassemble, screwing the base on makes the cup into a well-made permanent appliance. Thus, the screw enables someone who is not particularly skilled to build a strong appliance.

The early poskim debate this issue. The Magen Avraham (313:12) rules that screwing an appliance together constitutes a melacha min haTorah (see Shaar HaTziyun 313:32), Maamar Mordechai disagrees. In practice however, Maamar Mordechai concludes that one should follow the stringent ruling of the Magen Avraham, and this is the accepted halachic practice. Thus, screwing the cup together is considered manufacturing a cup.

Similarly, today one can purchase furniture that one takes home and assembles by oneself. Assembling this furniture is prohibited min haTorah even though it is made in a way that an unskilled person can assemble it. Thus, the definition of “skill and strength” is not whether the assembler needs to be skilled or strong, but whether the appliance is made into a permanent, well-made appliance.

BINOCULARS

Focusing a pair of binoculars involves turning a screw to make it tighter and looser. Does this violate boneh on Shabbos?

The poskim rule one may focus binoculars on Shabbos (Kaf HaChayim 313:73; Ketzos HaShulchan 119:12). They explain that there is a qualitative difference between screwing the base onto the cup, which creates an appliance, and screwing the binoculars, which is the method of using it. One may use an appliance, just as one may use a house by opening and closing the doors and windows. This is not building an extension onto the house, but is rather considered normal, daily usage. 

SHTENDER

Many shtenders are tightened and loosened by the use of a screw. May one adjust the shtender by loosening and tightening the screw? Does it make a difference how often one adjusts the height?

According to Rav Shlomo Zalman Auerbach and Rav Vozner, one may adjust the height of the shtender on Shabbos since this is considered using the shtender, not making a new appliance (Shulchan Shlomoh 313:7; Shu”t Shevet HaLevi 6:32; cf. Minchas Yitzchok 9:38, who prohibits).

SALTSHAKER

Question:

I forgot to fill the saltshaker before Shabbos, and now I realize that it is empty. May I unscrew the saltshaker on Shabbos to fill it, or is this considered demolishing and repairing the saltshaker?

Rav Shlomo Zalman Auerbach ruled that it is permitted to open, refill and close the saltshaker on Shabbos without violating boneh. Although the saltshaker is indeed screwed closed, it is typically not screwed as tightly as one screws furniture or the cup we described earlier (Minchas Shlomoh 1:11:4 s.v. gam nireh). The same applies to opening and closing a baby bottle. Although it is opened and closed by screwing, since it is intended to be opened and closed constantly, it is not considered demolishing and reconstructing it.

CONSTRUCTIVE WORK

We may ask ourselves, why is the screwing of a cup together or removing a window off its hinge considered a melacha? Both cases only take seconds to complete and are not at all strenuous.

Rav Samson Raphael Hirsch (Shmos 20:10) notes that people mistakenly think that work is prohibited on Shabbos so that it should be a day of rest. He points out that the Torah does not prohibit doing avodah, which connotes hard work, but melacha, which implies purpose and accomplishment. Shabbos is a day that we refrain from constructing and altering the world for our own purposes. The goal of Shabbos is to allow Hashem’s rule to be the focus of creation by refraining from our own creative acts (Shmos 20:11). Through not building for one day a week, we demonstrate and acknowledge the true Builder of the world and all it contains.