Comentario sobre Exodo 28:11

מעשה חרש אבן means THE WORK OF AN ARTIFICER IN STONES. This word חרש is in close connection (i. e. in the construct state) with the word that follows it and therefore it is punctuated with Patach in its last syllable. Similar is, (Isaiah 44:13) “The חָרַשׁ עצים stretcheth out a line” i. e. the worker in wood. So, also, (Isaiah 44:12) “the worker in (חָרַשׁ) iron maketh an axe.” All these examples of חָרַשׁ are in close connection with the words that follows them and are therefore punctuated with Patach.

מעשה חרש אבן, the words חרש אבן are in a construct mode; this accounts for the vowel patach under the letter ר in the word חרש. The meaning of the term is חרש של אבן, “a craftsman of gemstones,” someone expert in engraving. The reason why the vowel under the letter ח remains the kametz, is similar to the parallel mode of the word גנב, gannov, with the dagesh in both the letters ג and נ.

The work of one skilled with stones. . . Rashi is explaining that חרש is connected to אבן , so that חרש means “one skilled with stones.” Rashi says “stones” instead of “stone” [as in the verse], to tell us that “stone” means the category of stones, not a particular stone. [Rashi knows this] because one is not called skilled [by being skilled] with just a single stone.