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  • Writer's pictureCalvin Wu

Understand Your Drill Bit

The drill bit is an indispensable tool in CNC machining. Many people use it every day, but have you ever understood its design and the names of its parts?

Basic names of the parts of a drill bit

Knowing these basic parts is usually sufficient for most applications.

Professional names of the parts of a drill bit:

  1. Helix angle: Varies for different materials being drilled, typically between 10 to 40 degrees.

  2. Land: Guides and compresses the material, affecting hole accuracy and finish. Drill bits with double lands offer higher hole accuracy and finish.

  3. Chisel edge: The area between the land and the flute, which is lower than the land to reduce cutting resistance and friction in the hole.

  4. Flute surface: Sometimes called the primary cutting edge, it is used to evacuate chips from the hole.

  5. Point angle: Affects hole accuracy, located at the intersection of the land and the cutting edge.

  6. Primary cutting edge: The true cutting edge of the drill bit, formed by the angle between the two primary cutting edges and the point angle.

  7. Back face: The back of the chisel edge.

  8. Web: The section between the two flutes at the center of the drill bit. It carries 50% of the cutting forces (axial).

  9. Margin: The space created by the chisel edge, reducing friction between the drill bit and the material being drilled.

  10. Flute: The channel that creates space for chip evacuation."

How to improve issues of chipping and burring at the hole entrance?

Using a smaller point angle can improve the problem by ensuring that the drill point is supported by the width and height of the material being drilled.

A smaller point angle of 118 degrees:

  • Generates a radial cutting force with lower radial stability

  • Generates less axial force

  • Reduces hole chipping when drilling brittle materials

A larger point angle of 135-140 degrees:

  • Generates a larger axial force and has better radial stability

  • Allows for larger feed rates

  • Reduces burring when drilling soft or sticky materials

  • Improves roundness, diameter tolerance, and straightness of the hole

A drill bit with a chamfered edge:

  • Reduces chipping

  • Has the advantages of a larger point angle drill bit.

Common issues and solutions when using drill bits:

Rapid wear of the drill point:

Possible causes:

  • Insufficient clamping force on the workpiece, causing it to move downward under the drilling force and rebound after drilling, damaging the drill point.

  • Excessive vibration of the drill bit.

  • Insufficient clamping force of the drill chuck, causing the drill bit to slip under stress.

  • Inadequate rigidity of the machine tool.

  • Inadequate design or insufficient hardness and rigidity of the drill bit material.


  • Increase clamping force on the workpiece to prevent movement.

  • Reduce vibration by stabilizing the machine and/or reducing feed rate.

  • Ensure sufficient clamping force of the drill chuck.

  • Upgrade to a more rigid machine tool.

  • Choose a drill bit with better design and/or harder and more rigid material.

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