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Cutting Tool Anatomy

Bit Anatomy

In this example, using end mills, let us look at some common terminologies and typical anatomy. 

End Mill Definitions

  • Cutting Diameter – The size measured as a straight line across the center of a theoretical circle formed by the cutting edges as the end mill rotates.
  • Cutting Edge (Tooth) – The sharp edge of the end mill tooth
  • Flute – The deep spiral grooves behind each cutting edge that allow for chip formation and evacuation
  • Length of Cut (LOC) – The total measurement of the functional (sharp) cutting depth, this excludes any Flute Washout
  • Flute Length – Length of flutes, usually the same as Length of Cut, but can be different
  • Flute Washout – The amount of non-cutting flute area past the cutting edges
  • Overall Length (OAL) – The total measurement from one end of the end mill to the other, from the top (cutting end) to the bottom of the shank
  • Shank – The end of the end mill that is held in the holder
  • Shank Diameter – The size measured as a straight line across the center of the shank circle
  • Shank Flat – A flat area ground on the shank used to by a set screw to prevent pull out in certain types of holders. This could be referred to a Weldon Flat, Long Flat, or Tapered Flat
  • Helix Angle – The cutting edge angle measured from the centerline of the end mill to a straight line tangent along the cutting edge. See images
  • End Teeth – The teeth or cutting edges at the very top of the end mill, also known as axial teeth.
  • Side (Peripheral) Teeth – The teeth or the cutting edges on the side of the end mill, also known as radial teeth.
  • End Gash – the pockets on the end of the end mill that create the axial (end) teeth
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