Drill having construction suitable for enlarging previously formed hole

A drill for machining a hole in a workpiece, comprising:

• a cylindrical main body,
• a shank contiguous to said cylindrical main body where the shank is rotated about an axis of said cylindrical main body in a predetermined rotating direction, and
• an oil hole formed through said cylindrical main body and shank for delivering cutting fluid to an axial distal end portion of said cylindrical main body,
• wherein said drill is used to enlarge a hole previously formed in a workpiece through a die-casting process of the workpiece,
• wherein said cylindrical main body has flutes which are formed in said cylindrical main body and are extended from an axially distal end portion of said cylindrical main body toward said shank, so as to provide cutting edges in said axially distal end portion of said cylindrical main body,
• wherein said cylindrical main body has lands at peripheral portions thereof located between said flutes in a circumferential direction wherein each of said lands has a first margin provided at a front-side thereof as viewed in the rotating direction and a second margin provided at a rear-side thereof as viewed in the rotating direction, where said first margin has a thickness larger than that of said second margin in the rotating direction,
• wherein an end opening of said oil hole has a circular shape and is located closer to said first margin than to said second margin,
• wherein said cutting edges cooperate with each other to define a point angle which is larger than 170° and is smaller than 180°,
• and wherein each of said cutting edges is curved such that said each of said cutting edges is convexed in a direction toward said axially distal end portion as seen in a direction perpendicular to said axis.