Calculate the exact drill point length for your machining operations. This tool helps CNC programmers and machinists determine how much deeper a drill must travel to reach full diameter depth based on the point angle.
Drill Point Calculator
Drill Point Length (L):
—Drill Point Calculator Formula
The geometric relationship between the drill diameter and the point length is derived from trigonometry.
Source: Engineering ToolBox – Drill Bit Angles
Variables:
- L (Drill Point Length): The axial distance from the tip of the drill to the shoulder where the full diameter begins.
- D (Drill Diameter): The nominal diameter of the drill bit being used.
- θ (Point Angle): The included angle of the drill point (typically 118° for general purpose or 135° for hard materials).
What is a Drill Point Calculator?
A Drill Point Calculator is a specialized engineering tool used to determine the additional depth a drill bit must travel to achieve a specific hole depth. When drilling a hole, the conical tip (the point) enters the material first. If you need a flat-bottomed hole or a specific depth at the full diameter, you must account for this tip length.
For CNC machining and manual milling, calculating the “Drill Point Compensation” is critical for avoiding tool collisions and ensuring part accuracy, especially in blind hole applications where the thickness of the remaining material is minimal.
How to Calculate Drill Point Length (Example)
Let’s calculate the point length for a standard 1/2 inch drill bit with a 118-degree point angle:
- Identify Diameter (D): 0.500 inches.
- Identify Point Angle (θ): 118 degrees.
- Calculate Half Angle: 118 / 2 = 59 degrees.
- Calculate Tangent: tan(59°) ≈ 1.6643.
- Divide Radius by Tangent: (0.500 / 2) / 1.6643 = 0.250 / 1.6643 ≈ 0.1502 inches.
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Frequently Asked Questions (FAQ)
The most common standard angle is 118° for general-purpose high-speed steel (HSS) drills used on soft steels and cast iron.
135° points are typically found on split-point drills and are better suited for harder materials like stainless steel, as they require less thrust and don’t “walk” on the surface.
No, the point length only affects the depth. The diameter is determined by the body of the drill bit.
If you don’t account for the point length, the tip might break through the bottom of the workpiece before the full diameter reaches the desired depth.