Prior to conventional drilling on an engine lathe, to what depth should the center drill be fed?

Prior to conventional drilling on an engine lathe, to what depth should the center drill be fed?

• A. Half the center drill's taper length
• B. The full taper length
• C. Half the center drill's overall length
• D. One quarter of the taper length

Answer: (A)

Center drilling establishes a true center and provides a precise starting guide for the drill that will follow. Feeding the center drill about halfway along its taper lets the conical portion form a reliable center without cutting too deeply into the work or weakening the drill tip. This depth creates a stable, accurate center that the subsequent drill can follow, which helps keep the hole true and concentric with the axis. If you go deeper than halfway, you risk excessive cutting, possible tool chatter or breakage, and a center that’s less controllable. If you don’t cut enough, the center may not be formed well enough for reliable guidance. Half the taper length is the best compromise.

Center drilling establishes a true center and provides a precise starting guide for the drill that will follow. Feeding the center drill about halfway along its taper lets the conical portion form a reliable center without cutting too deeply into the work or weakening the drill tip. This depth creates a stable, accurate center that the subsequent drill can follow, which helps keep the hole true and concentric with the axis.

If you go deeper than halfway, you risk excessive cutting, possible tool chatter or breakage, and a center that’s less controllable. If you don’t cut enough, the center may not be formed well enough for reliable guidance. Half the taper length is the best compromise.