The anatomy of an end mill

Wednesday, January 16, 2019

Engineering can be a scary concept. With the hundreds of cutting tools alongside endless amounts of applications so it can be overwhelming knowing the right tool to select first time.

We understand how critical it is for a job to be complete first time round, that is why here at ACT we only sell the right tool first time...

So we thought we would share our years of expertise and give you and insight into selecting the right tool first time. See below a short article on the anatomy for an end mill.


Flutes are the easiest part of the end mill to recognise. The flutes are deep spiraled grooved in the tool that allow for chip formation and evacuation. During the tool selection is it important to take flute count into consideration. 

Generally, the lower the flute count the larger the empty spaces between the cutting edges. This void effects tool strength but also allows for larger chips with heavier depths of cut (aluminium for example). When machining harder machining materials, such as steel, tool strength becomes a larger factor and higher flute counts are often utilised.


The profile refers to the shape of the cutting end of the tool. It is typically one of 3 options:

Square Profile - Tooling features with sharp corners that are squared off at the 90 degree angle.

Corner Radius - This type of tooling breaks up a sharp corner with a radium form. This rounding distribute cutting forces more evenly across the corner, helping to prevent wear or chipping while prolonging the tool life.

Ball Profile - The type of tooling features flutes with no flat bottom, rounded off at the end creating a ball nose at the tip of the tool.

Cutter Diameter

The cutter diameter is often the first thing that machinists look for when choosing a cutting tool for their job. This dimension refers to the diameter of the theoretical circle formed by the cutting edges as the tool rotates.

Shank Diameter

The shank diameter is the width of the shank - the non-cutting of the tool that is held by the tool holder. This measurement is important to note when choosing a cutting tool to ensure the shank is the correct size for the corresponding tool holder. 

Overall Length & Length of Cut

Overall length is easy to decipher as it is the measurement between the two axial ends of the tool. The difference between this and the length of cut is the LOC is the measurement of the functional cutting depth in the axial direction.

Overall Reach / Length Below Shank

An end mill's overall reach or length below shank is a dimension that best describes the necked length of reached tools. It is measured from the start of the necked portion to the bottom of the cutting end of the tool. The neck relief allows space for chip evacuation and prevents the shank from rubbing in deep-pocket applications.

Helix Angle 

The helix angle of a tool is measured by the angle formed between the centreline of the tool and a straight line tangent along cutting edge. A higher helix angle used for finishing wraps around the tool faster and makes for a more aggressive cut. A lower helix angle wraps slower and would have a stronger cutting edge, optimised for the toughest roughing applications.


Pitch is the degree of radial separation between the cutting edges at a given point along the kength of cut, most visible on the end of the end mill. Similar to a variable helix, variable pitch tools have non-constant flute spacing, which helps to break up harmonics and reduce chatter. The spacing can be minor but still able to achieve the desired effect.

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