I'm a TT assistant professor at a R1 school, and I just recently accepted an offer from a private company. I'm planning to talk with the department head and let him know and I was wondering if anyone has any thoughts how to approach this (with maybe examples if you have anything in mind) and quit gracefully ? Also do you think one month ahead is enough to let him know before the departure ?
Update: Ok, just wanted to share some update. I talked with the head today and something along this answer from @caleb-stanford worked really well.
For example: "While I have really enjoyed my time here, it's become increasingly clear to me that being in academia long-term is not the right fit. In addition, I have personal and family constraints that would require me to be away from for extended periods of time, and make having a more flexible work location a necessity for me in the future. I have nothing but positive things to say about . I'm sorry for the short notice; I'm letting you know as soon as possible, so that you can hopefully work to make plans accordingly for my departure."