Safety must be top priority, and the time needed to go through the checklist must be factored in for every tool change when using the CNC machines we have (i.e. where tool changes are manual). As a start the list here is similar to Titan's but customized to work with our CNC machines:
Note: This list is somewhat different because our machine is different, and also is written from some experiences that have happened with the machine.
The simulation of the CAM program can be a part of the post process where it created gcode and then use the backplot feature to inspect the run. This task is good for the operator to get an idea what is about to happen so that he can know what to expect when doing a dry run. I'd recommend to do this for the one tool job that is about to be done on the one gcode, per tool change.
See CNC 101 under Preparing the stock for more details.
See CNC 101 under Zero'ing X and Y axis and Zero'ing the Z axis for more details.
Note: we don't have as much height clearance, and usually milling has shallow passes. I may revise this once Mega V is running. For M3, I test around 0.5" inch above. The most important reason for this is to ensure the zaxis doesn't have any unexpected dips (these are hard to spot in the simulation), also ensure there is no interference with the mounting jigs. This is something that may happen more so with the fact that we will have nested parts that utilize the entire sheet. For the M3, I can reserve the outer 2" perimeter for the jigs, but they need to be angled to do so. You do not have to follow this in certain scenarios, but then the dry run can ensure no interference.
This is mostly self explanatory, but I'll add to this what you really to check is the offsets. The M3 tends to have unexpected physical things happen during a run or tool change such as the belt slipping or the Z-axis router mounting plate shifting. I tend to solve this by drilling a small divot on the point of origin (usually the center) and have the tool hovering above this and I jog there and closely look at this from front and side view.
The milling has to move fast enough to cool down to new stock material, so you must not slow it down, instead keep an active watch and ready to push the pause. In addition you may wish to manually apply lubricant when it sounds crunchy. If the crunchy sound doesn't go away your bit may be gummed up. This is more-so for lexan. Pause it... Unlike 3D printing you can't let it go without being watched, but you can start from where you left off, and the tool job is usually much quicker. Don't worry about time loss... if there is anything that doesn't look or sound right hit the pause. We don't have an e-stop, but should something catastrophic about to happen... pull the plugs literally or manually turn off the router.