I recently drilled a 1/2in hole in the sheet metal on the inside of a door panel, and the result was less of a hole and more of an ugly, asymmetrical gash as the metal deformed under the stress of the drill. I had to use cutters to cleanup metal which bent out of plane.
Now I need to drill a hole in the firewall to run a new harness, and I'd like to do it right this time. How can I ensure that I drill a clean, circular, 1/2in - 1in hole in the firewall? Should I use a specialized bit? Do I run the drill at max speed?