Machinists often use the terms long length and long reach end mills interchangeably, but each tool is designed for a specific machining purpose. Selecting the correct end mill can improve rigidity, reduce chatter, extend tool life, and produce a better finished product.
Long length end mills (also known as long flute end mills) are the more common of these two style and feature extended flute length and overall tool length compared to standard or long reach end mills. They are designed for machining deeper slots, pockets, cavities, and tall walls where additional cutting depth is required.
Because the cutting flutes are longer, these tools allow greater axial engagement and are well suited for:
The added flute length, however, reduces rigidity. As tool length increases, so do the risks of chatter, tool deflection, poor workpiece surface finish, and tool breakage. To maintain stability and accuracy, machinists often reduce feed rates and cutting forces when using long length tools.
Long reach end mills (also known as reduced neck, long neck, or extended reach end mills) are engineered specifically to access hard-to-reach features. They have a reduced neck diameter and shorter flute length, allowing the cutter to extend farther into confined spaces than long length end mills.
Since only a shorter portion of the tool is actively cutting, long reach end mills are generally more rigid than comparable long length tools. This increased rigidity helps reduce chatter and tool deflection while improving dimensional accuracy and surface finish.
The tradeoff is reduced side-cutting capability. Because the flute length is shorter, axial depth of cut is more limited than with long length end mills.
To determine the total reach of a long reach end mill, add the neck length to the flute length.
Note: Flute length may also be referred to as Length of Cut (LOC) or Depth of Cut (DOC).
Typical applications include:
The best tool depends on the machining objective:
|
Feature |
Long Reach End Mill |
Long Length End Mill |
|
Primary Design |
Reduced neck with shorter flutes |
Extended flute length |
|
Main Purpose |
Reach deep cavities and tight areas |
Machine deep walls and slots |
|
Flute Length |
Shorter |
Longer |
|
Reach |
Excellent |
Good |
|
Rigidity |
Higher |
Lower |
|
Chatter Resistance |
Better |
Poorer |
|
Tool Deflection |
Lower |
Higher |
|
Side Milling Capability |
Limited by flute length |
Excellent |
|
Axial Depth of Cut |
Limited |
Greater |
|
Workpiece Surface Finish |
Usually better |
Can degrade from vibration |
|
Tool Strength |
Stronger near cutting end |
Weaker due to long flutes |
|
Typical Applications |
Mold cavities, deep pockets, aerospace work, etc. |
Deep slotting, profiling, tall wall machining, etc. |
|
Typical Uses |
Use a long reach end mill when you need to reach deep into a cavity. |
Use a long length end mill when you need to machine deep walls or slots. |
For the best performance and results:
Tool deflection is the bending or flexing of a cutting tool caused by machining forces. As tool length increases or diameter decreases, the tool becomes less rigid and more prone to bending.
Excessive tool deflection can result in:
Chatter is unwanted vibration during machining. It can produce:
Common causes include:
Tool stickout, is the distance the cutting tool extends from the holder or collet to the tool tip.
Greater stickout reduces rigidity and increases the likelihood of:
These concepts are closely related:
More Tool Stickout → More Tool Deflection → Greater Chance of Chatter
That is why machinists try to:
Reducing tool stickout is often one of the fastest and most effective ways to improve machining stability, surface finish, and tool life.