Flat bottom drills can be sharpened on the M-series. A gun drill is a single flute drill and cannot be sharpened on Darex sharpeners. Like an end mill for wood, they can be sharpened on Darex end mill sharpeners, if their profile is like a metal cutting end mill. Wear begets wear. When a tool is dull, the increased friction generates excessive heat thus tools wear faster.
Dullness increases torque and thrust requirements.
Tool becomes hot. A visible blue discoloration will appear. Tool produces a squealing noise. Rounding of the outside corners of the tool. While it is true that aluminum oxide wheels are inexpensive, we believe that super abrasive wheels are a better value.