The formation of the shin in the bayit of the head Tefillin
Jewish law requires that the two shin`s in the sides of the bayit of the head Tefillin be embossed in the leather of the bayit itself. This is performed as follows:
The two sides of the ketzizah are moistened with a wet sponge for two hours.
After the leather becomes pliable, pressure is applied with the press and a metal plate in the form of an inverted shin to the exact position where the letter shin is to protrude from the finished head Tefillin. This phase of the production process generates a halakhic problem known as "chok tokhot" (referring to the inner part [tokh] of the shin), since the shin was formed by pressure on the vicinity of the shin.
The shin that was embossed is painted with a noticeable color, other than black, so that it can be identified. The protruding shin is returned to the press and the shin is pushed back inwards, into the leather of the bayit. After this operation of the press, the shin no longer protrudes, but remains visible. The shin is once again raised manually, with a special knife, by delicately and carefully applying pressure to the shin itself. We have now formed a shin that projects from within the ketzizah, and that is made of the leather itself.
After the letter has been raised, and it looks like a shin, the shape of the letter is improved by using the metal die and the hydraulic press.
After the formation of the shin, the bayit and the titora are given an exact square shape, using a precise lathe and a digital micrometer (a precision scientific measuring instrument). This tool, that is used for measuring in engineering operations and in high-tech industries, aids in the exact measurement of the sides and the formation of a precise and perfect square.