Drill Tip Length Calculator

| Added in Construction

How to Calculate Drill Tip Length

The drill tip length calculator helps machinists and manufacturers determine the length of a drill bit's conical tip based on the drill diameter and tip angle. This measurement is crucial for precision drilling operations and tool design.

Formula

The drill tip length is calculated using:

$$\text{Drill Tip Length} = \frac{D / 2}{\tan(\alpha / 2)}$$

Where:

  • D = Drill diameter (inches or mm)
  • (\alpha) = Tip angle (degrees)
  • DTL = Drill tip length (same units as diameter)

Calculation Steps

  1. Measure the drill diameter - The full diameter of the drill bit
  2. Identify the tip angle - Most common is 118 degrees for general purpose drilling
  3. Divide diameter by 2 - Get the radius
  4. Calculate half the tip angle - Divide tip angle by 2
  5. Find the tangent - Convert half-angle to radians and calculate tan
  6. Divide radius by tangent - This gives the tip length

Example Calculation

For a drill with 8 inches diameter and 60 degree tip angle:

$$\text{DTL} = \frac{8 / 2}{\tan(60^\circ / 2)} = \frac{4}{\tan(30^\circ)} = \frac{4}{0.577} \approx 6.93 \text{ inches}$$

Common Tip Angles

  • 118 degrees - Standard twist drill, general purpose
  • 135 degrees - Split point drill, harder materials
  • 90 degrees - Center drill
  • 60 degrees - Spotting drill
  • 180 degrees - Flat drill (zero tip length)

Frequently Asked Questions

Drill tip length is the axial distance from the outermost cutting edge of the drill bit to the point where the conical tip meets the cylindrical body of the drill. It's also known as the chisel edge height or tip height.

The tip angle affects cutting force, material suitability, chip evacuation, and tool life. Different materials work best with specific angles, and proper angle selection reduces wear.

A tip angle that's too small (acute) creates a longer, more pointed tip that requires higher thrust force, is more prone to breakage, works better for harder materials, and provides better centering.

A larger (obtuse) tip angle creates a shorter, flatter tip that reduces thrust force needed, drills faster in soft materials, may wander on initial contact, and generates more heat.

Use a drill point gauge or protractor to measure the included angle at the tip. Place the gauge flush against both cutting edges and read the angle. Most hardware stores sell inexpensive drill point gauges.

Yes, you can regrind a drill bit to a different tip angle using a drill bit sharpener or grinding wheel. This is common when adapting general-purpose bits for specific materials like plastics, aluminum, or hardened steel.

For stainless steel, a 135-degree split point drill is recommended. The wider angle reduces thrust force and the split point improves centering and reduces walking on hard surfaces.

The tip length must be accounted for when calculating total drilling depth. If you need a hole with a specific flat-bottom depth, you must drill deeper by the tip length amount to achieve the full depth.