I'm a newbie and am hoping to get some guidance on enlarging and re-tapping. I have a steel reducer bushing that has 3/8" NPT female threads that needs to get to 1/2-28. From what I've read I need a 15/32" drill bit to create the hole for my 1/2 tap. Can I drill directly into the existing 3/8" tapped hole in one pass, or should it be done using slightly bigger bits in each pass? I plan on using a manual drillpress, a cobalt 15/32" bit, and plenty of cutting oil. What would be a good rotational speed of the press? I'd appreciate any help or guidance, thanks!