Quote Originally Posted by biketrialsdave View Post
I was wondering if a step drill (13mm max diameter) would be a better idea for enlarging as it would be self centering?
Step drills are intended more for sheet metal. I would get a decent hss twist bit. You can pick up dormer bits on eBay for very little. http://www.ebay.co.uk/ulk/itm/140928964799