드릴 선단각 비교: 118° vs 135° 분할 포인트

1. 118° Conventional Drill Point

The standard 118° included angle has been the industry benchmark for over a century. The sharp cone allows easy penetration in ductile metals such as low-carbon steels, aluminum alloys, and brass.

However, because standard 118° drills possess a non-cutting straight chisel edge across the center web, the drill tends to "walk" or wander across the workpiece surface unless guided by a center drill or punch mark. The central chisel zone rubs and extrudes material rather than shearing it cleanly.

2. 135° Split Point (Self-Centering)

The 135° split point drill features additional grind facets on the chisel edge that create two secondary cutting lips extending right to the center axis. This geometry provides multiple key benefits:

• Zero Walking / Self-Centering: Starts cleanly on curved pipe or flat plate without needing a center drill.
• Reduced Thrust Force: Reduces machine axial feed pressure by 40% to 50% by eliminating the blunt chisel rubbing zone.
• Flatter Point Length: Point length is only 0.207×D (compared to 0.300×D for 118°), providing greater flat cylindrical depth in blind holes.

3. Point Length Trigonometric Formula

To calculate how far the conical tip protrudes beyond the cylindrical drill body, use simple right-triangle trigonometry: