Cleanliness is key to achieving good runout control when assembling tool holders. Small particles or oil in a tool holder can cause large runout of the cutting tool, deceasing tool life and performance.
A pilot or spot drill, also known as a starter drill, is typically required when the succeeding drill is longer than 10xD or smaller than Ø 1.00 mm. Starter drills can also be used to improve hole location due to their short, rigid geometries.