As machinist I run out of tp in every turn. The only turn where it's not a problem is a1 since jumps give a good breathing room to naturally regen tp + invo.
A2 is extremely tp taxing for machinist by the time the widows spawns I run full tp promotion into the next wave. If you don't have tp issues in a2 I would assume u simply don't aoe :/ (my last night parse was roughly 1.5k)
A3 is fine till after the adds phase. You and your melees should start to have tp issues after the hand that grabs the healers die, here I run promotion till the next invo is up.
A4 pretty much the last phase is huge tp drain especially if you mess time ur invigorate earlier. You should time it that u have invo up right after ur first Rez. Otherwise you will need tp promotion. Your melees should call out for tp eventually during the last phase as well.