I got two done at lunch with our fancy drill press. I say fancy as it's almost a milling machine with its adjustable bed. I just stepped up the drill sizes until I hit 5/16". The first one was close to center and the second one was dead on. I used window cleaner as a coolant, it was handy, and did no damage to the rubber. Just gotta go slow and steady. I hope to get the other two done tomorrow.