Centre Cutting vs. Non-Centre Cutting End Mills: A Guide to Their Differences

End mills are fundamental cutting tools in milling operations, used to remove material and create various shapes, slots, and profiles. A key distinction between different types of end mills lies in their ability to cut axially, or plunge, into material. This capability is determined by whether the end mill is "centre cutting" or "non-centre cutting." Understanding this difference is crucial for selecting the correct tool for a specific machining task.   

The primary difference between centre cutting and non-centre cutting end mills lies in the geometry of their cutting edges at the very centre of the tool face.   

Centre Cutting End Mills:

Centre cutting end mills have cutting edges that extend all the way to the centre of the tool. This design allows them to cut while plunging directly into the material, much like a drill bit. The flutes are ground in such a way that there is a cutting edge present at the rotational axis of the tool.   

• Key Feature: Cutting edges meet at the centre.
• Capability: Can plunge axially into material.   
• Typical Applications:
  • Slotting: Creating slots by plunging and then moving laterally.
  • Pocketing: Machining enclosed areas by plunging and then clearing out the material.   
  • Plunge Cutting: Entering the workpiece directly from the top surface.
  • Ramping: Entering the material at an angle.

Centre cutting end mills are versatile and essential for operations that require starting a cut in the middle of a workpiece or creating enclosed features. They are commonly available in various flute counts, with 2 and 3-flute designs often favoured for their chip evacuation capabilities, which is important when plunging.   

Non-Centre Cutting End Mills:

Non-centre cutting end mills, on the other hand, do not have cutting edges that extend to the absolute centre of the tool. There is typically a small relief or a gap at the centre where the cutting edges do not meet.

• Key Feature: No cutting edge at the exact centre; there is a relief or gap.
• Capability: Cannot plunge axially into solid material.
• Typical Applications:
  • Side Milling: Removing material by cutting along the periphery of the tool.
  • Peripheral Milling: Cutting the outside profile of a workpiece.
  • Shoulder Milling: Creating a step or shoulder on a part.
  • Copy Milling: Following a contour to create a shape.

Non-centre cutting end mills are primarily designed for operations where the tool enters the material from the side or is already in a pre-drilled hole or cavity. Attempting to plunge a non-centre cutting end mill into solid material will likely result in tool deflection, breakage, and poor surface finish because there is no cutting action at the point of entry.

In Summary:

Choosing between a centre cutting and non-centre cutting end mill is dictated by the specific machining operation you intend to perform. For any task requiring the tool to enter the material by moving straight down, a centre cutting end mill is necessary. For operations that only involve cutting along the sides of the tool, a non-centre cutting end mill may be suitable and can sometimes offer better rigidity for side milling applications. Always ensure you are using the correct type of end mill for the intended application to achieve optimal results and prevent tool or workpiece damage.