Cutting Diameter (ØD): The diameter of the cutting edge.
Overall Length (OAL): The total length from the tip to the end of the shank.
Cutting Length / Flute Length (CL): The effective cutting length of the tool.
Shank Diameter (Ød): The diameter of the shank, usually equal to or larger than the cutting diameter.
Standard Proportion
Cutting length (CL) ≈ 1.5 × D
Overall length (OAL) ≈ 3 × D
Example:
-Ø10mm end mill → CL ≈ 15mm, OAL ≈ 60–75mm
-Ø20mm end mill → CL ≈ 30mm, OAL ≈ 90–120mm
Long Flute Type
Designed for deep slots or cavities.
Cutting length can reach 3D – 5D.
Lower rigidity, more prone to vibration, requires reduced cutting parameters.
Extra Long / Long Reach Type
Overall length can reach 5D – 10D.
Used for deep cavity or mold machining.
Shank is often reinforced (thicker) to increase rigidity.
Rigidity: Larger diameter = higher stiffness, stronger against bending. Smaller diameter + long length = easy to break.
Stability: Small diameter with long reach is prone to chatter.
Application: Deep cavities and narrow slots require longer flute length.
Small diameter (Ø1–3mm) → OAL typically 38–50mm, flute length ≤ 2D.
Medium diameter (Ø4–12mm) → OAL 50–75mm, flute length ≤ 3D.
Large diameter (Ø16mm+) → OAL 100–150mm, can be designed as long or extra long.
High-precision machining → Always choose shorter flute and shorter OAL for better rigidity.
Summary
Larger diameter → can have longer length
Smaller diameter → should be kept shorter
Standard ratio: CL ≈ 1.5D, OAL ≈ 3D
Long or extra-long tools are only for special applications and require reduced cutting parameters
