The answer is that the Torah never states that one must “write” a shin on the side of the tefillin. The halacha leMoshe miSinai merely states that there must be a shin on the side of the tefillin, without specifying that the shin must be written there. Therefore, the lenient opinions contend that there is no requirement to “write” a shin on the tefillin, and it is sufficient for the shin to be made in any way, even through chok tochos. As mentioned above, we paskin that the shin should be formed in a direct way first.
Tefillin must be square
There is another halacha leMoshe miSinai that the tefillin must be perfectly square (Menachos 35a). The rishonim dispute whether min haTorah both the bayis and the titura must be square, or only one of them. Since this matter is a controversy, and, furthermore, since some opinions require that they must both be square, accepted practice is that both the bayis and the titura be perfectly square.
The width of the bayis must be the exact same measurement as its length, and there may be no nicks, indentations, or bulges that ruin its perfect squareness. The height of the tefillin does not need to be the same as the width and length (Rambam, Hilchos Tefillin 3:1). As a matter of fact, some batim machers deliberately make tefillin that are taller than they are wide. This is so that the tefillin will fit properly on the arm, without requiring that the parshios be made very small.
Similarly, the titura is shaped so that its length and width are equal.
In order to get the four compartments of the shel rosh to form a perfect square, many batim machers paste the sections of the bayis together to help them hold together. Although there is much halachic controversy about gluing the compartments together, many prominent poskim in earlier generations permitted it (such as Yeshuas Yaakov 32:24; Shu”t Chasam Sofer Orach Chaim #5, however cf. Vol. 6 #68; Shu”t Beis Yitzchok, Orach Chaim 7:6; Daas Torah 32:40).
Other poskim permit gluing the compartments only if the paste is applied to less than half the height of the wall of the compartment and is not applied along the outside edges.
However, since there are poskim who disapprove of using any paste, it is certainly a hiddur not to use any at all (Chayei Adam 14:4). These batim are referred to as “perudos ad hatefer legamri,” which literally means, separated completely down to the stitch, referring to the stitching on the top of the titura (which will be explained later).
Germane to this discussion is a well-known ruling from Rav Chaim Volozhiner. When asked whether pasting the compartments of the shel rosh together is permitted, he responded that he would not permit it, because the two gedolei hador of the previous generation, the Vilna Gaon and the Shaagas Aryeh, both contended that pasting the compartments invalidates the tefillin.
In earlier generations, when tefillin batim were made from much softer calf leather or even flimsier parchment, it was very difficult to make tefillin that would remain square unless the compartments were pasted together. However, today’s gasos batim are kept square through the stiffness of the hide and the pressure of the hydraulic press. Since the gasos batim are not dependent on paste to hold their shape, many contemporary poskim contend that one should refrain from placing any paste in the batim.
Why not glue?
What is wrong with gluing the compartments together?
The problem is that the shel rosh is required to have four separate compartments, one for each parsha. The poskim who prohibit pasting the compartments contend that glue makes them into one connected compartment, thus invalidating the tefillin. Those who are lenient contend that pasting the compartments together does not halachically make them into one compartment.
The compromise position contends that the compartments are considered separate, if they are pasted less than half way up and the outside edge is clearly not connected. This makes the batim noticeably separate, which they contend is all that is required. Ask one’s rav whether one should request batim in which no paste was used, at all.
The titura
The titura consists of two parts, the widening at the bottom of the ketzitzah (upper titura) and the flap that closes and seals the parshios inside (lower titura). In gasos tefillin, the titura is formed out of the same piece of leather as the ketzitzah. The lower titura is bent 180 degrees until it is directly beneath the upper titura. The gap between the two is filled with pieces of leather, and then the hide is shaved until it is perfectly square.
At one point in time, ordinary scrap leather was often used as filler, but this is rarely done today. Although batim using ordinary scrap leather as filler are kosher, it is preferable that the filler be hide that was tanned lishmah (Shu”t Minchas Yitzchak 6:1). This is standard contemporary practice.
Some poskim contend that it is acceptable to fill small nicks in the side of the titura with glue. Others feel that it is not kosher, lechatchilah, to do this, but that nicks should be patched with hide or parchment tanned lishmah (Shu”t Minchas Yitzchak 6:1; Shu”t Shevet Halevi 3:2; 9:4).
When the titura is completed and perfectly square, twelve holes are punched through it so that it can later be stitched closed. The stitching must also be square. Therefore, it is vital that these holes form a perfect square and that they are not too large (which may cause the stitching not to be square).
At this point, the batim are almost ready, except that they need painting and the parshios have not yet been inserted. One minute — we have not yet discussed the writing of the parshios. We also need to talk about the processing of the retzuos, the finishing and sewing of the titura, and various other hiddurim of tefillin.
