Greenlee punches are an easy way to create holes in metal. You drill a 3/8" hole, then insert the die and leadscrew thru the hole, then screw the punch portion onto the leadscrew. Using a wrench, turn the leadscrew, which draws the punch thru the metal into the die, leaving a clean hole with smooth edges. It takes seconds. Punches are available for holes ranging from 1/2" to over 4-inches (the large punches can't be easily pulled with a hand wrench). Metric sizes are also available.
The part number for the 3/4-inch size is 730-3/4.