Our guild downed Fabricator last week.
We used only the right and left cannons. Your choice may vary because in Normal mode, all 3 cannons will apply the molten armor debuff. So whatever gets your fire blast going faster, use it.
1. We had 2 tanks switching off for each other every 5th-6th armor debuff stack.
2. DPS killing stun droids when they spawned ASAP, burning the boss with CD's when we were able to blast him with the molten armor debuff.
Up top, we had 2 people doing the puzzle. Make sure your puzzle-solvers are familiar with the mechanics of the puzzle and can do it without calling out who needs to move at every piece (we found that more confusing than just learning the puzzle).
When the mine droids spawned in front of the panels, we used knockbacks on the left/right panels, and burned down the one at the middle panel, and then continued to proceed.
Call out when the puzzle is ready to fire, and make sure your team down below confirms it's clear to fire. The cannon will one-shot anyone caught in the fire area.