Learn Italian: Mi faccio accorciare l'orlo dal sarto. - I have the hem shortened by the tailor.

In Italian, the causative construction (fare + infinitive) means to have someone else do an action. Adding a reflexive pronoun (farsi + infinitive) specifically means you are having it done for yourself. So mi faccio accorciare literally translates to "I have [it] shortened for myself."

In English we say "have the hem shortened," putting the object in the middle. Why doesn't Italian do this?

In the Italian causative construction, the conjugated form of fare and the infinitive verb must stay glued together. You cannot separate them with the object like you do in English. It is always faccio accorciare l'orlo (literally "I make shorten the hem"), never faccio l'orlo accorciare.

Why is the tailor introduced with dal?

When you use the causative construction and want to mention the person who physically performs the action, you introduce them with the preposition da (by). Here, it combines with the definite article il to become dal sarto (by the tailor).

If I wanted to say this in the past tense ("I had the hem shortened"), which auxiliary verb would I use?