Drill Point Length Calculator
Enter diameter in Inches or Millimeters (results will match input unit).
Common angles: 118°, 135°, 90°
Calculated Point Length (L)
0.0000
What is a Drill Point Calculator?
This Drill Point Calculator helps machinists, CNC programmers, and engineers determine the exact length of the conical "tip" of a twist drill. Understanding this dimension is critical for precision drilling operations, particularly when calculating the total depth required to achieve a full-diameter hole without breaking through the bottom of the material.
Why Calculate Drill Point Length?
When you program a CNC machine to drill a hole to a specific depth, the machine usually measures the depth from the tip of the drill (the very point). However, because the drill has a conical point, the full diameter of the hole is not achieved until the drill has penetrated deep enough to bury that point.
- Blind Holes: If you need a full-diameter hole to a specific depth but cannot drill through the part, you must add the drill point length to your program depth.
- Through Holes: To ensure the drill breaks through clean without unnecessary over-travel, calculating the point length helps optimize cycle times.
- Spot Drilling: For chamfering with a 90° spot drill, the point length calculation helps determine the Z-depth required to create a specific chamfer width.
The Drill Point Formula
The calculation relies on simple trigonometry based on the drill diameter and the included angle of the drill point. The formula used is:
L = (D / 2) / tan(A / 2)
Where:
- L = Point Length
- D = Drill Diameter
- A = Included Point Angle (in degrees)
Common Drill Point Angles
Different materials and drilling applications require different point angles. Here are the standards:
- 118°: The standard angle for General Purpose High-Speed Steel (HSS) drills. Suitable for mild steels, aluminum, and wood.
- 135°: Common for Cobalt and Carbide drills. Used for harder materials like stainless steel to reduce walking and heat generation.
- 90°: Typically used for Spot Drills and Centering Drills. This angle allows the spot drill to also create a 45° chamfer on the hole edge.
- 150°+: Often found on high-performance carbide drills for deep hole drilling to reduce thrust forces.
Rule of Thumb
While this calculator provides precision, many machinists use a quick rule of thumb for standard 118° drills: Length ≈ 0.3 × Diameter. For 135° drills, it is approximately 0.2 × Diameter.