When it comes to precision milling—whether you're crafting molds, cutting complex cavities, or performing high-speed machining—the Corner Radius End Mill is a staple in any machine shop. But within this tool category, there are three common variations that often raise questions for engineers, tool buyers, and CNC operators alike：

1. Straight Corner Radius End Mill

2. Reduced Shank Corner Radius End Mill

3. Long Neck Corner Radius End Mill

They might look similar at first glance, but each type is designed with specific structural and functional differences in mind. In this guide, we'll break down what sets them apart and how to choose the right one for your application.

What Is a Corner Radius End Mill

A Corner Radius End Mill is a cutting tool whose tip features a slight radius instead of a sharp 90-degree angle. This reduces stress concentrations at the cutting edge and enhances tool life. Compared to flat-end mills, corner radius types offer a smoother surface finish, increased durability, and better performance in applications requiring repeated passes or high loads.

Straight Corner Radius End Mill

Structure:

This is the most standard type. It features a uniform shank and cutting diameter, with a corner radius at the tip for stress reduction.

Pros:

High rigidity due to short flute length and straight shank

Ideal for achieving clean, accurate cuts

Long tool life with proper use

No interference risk from shank geometry

Best For:

General-purpose milling on mold steels, stainless steels, and carbon steels

Flat surfaces, shallow cavities, and shoulder milling

3-axis CNC machines with unrestricted access

If your application doesn’t require deep reach or complex access angles, the straight corner radius design offers the most balance in rigidity and versatility.

Reduced Shank Corner Radius End Mill

Structure:

The cutting diameter is larger than the shank diameter, which allows the tool to work deeper without shank interference. The reduced diameter begins right behind the cutting flutes.

Pros:

Extended reach with minimal risk of tool interference

Ideal for side milling and deep slotting

Improved tool access in multi-axis machining setups

Best For:

Deep cavity mold work

5-axis or multi-axis machining centers

Situations where the tool must pass through narrow spaces before cutting

If you're often dealing with deep, narrow cavities or workpieces with interference-prone geometry, the reduced shank version is a clear winner.

Long Neck Corner Radius End Mill

Structure:

This variation features an extended neck section between the cutting flute and shank, enabling longer reach into very deep or narrow regions while keeping the cutting diameter small.

Pros:

Allows entry into extremely deep or recessed areas

Maintains small cutting diameter with long overhang

Suitable for fine detail and hard-to-reach zones

Best For:

Deep pocket milling, fine cavities, and rib machining

Internal mold features

5-axis machining in complex geometries

Some long neck models also incorporate reduced shank features, offering the best of both worlds.

Comparison Table

How to Choose the Right Tool

When selecting between these three end mill types, consider

1. Part Geometry Deep pockets or narrow channels Go with reduced shank or long neck

2. Tool Rigidity Needs If stiffness and minimal deflection are essential, the straight version is your best bet

3. Machine Type 3-axis machining is more suited for straight tools; 5-axis setups benefit from the clearance of reduced shank or long neck

4. Cutting Depth Long neck excels in ultra-deep cutting, especially when combined with slow feed rates and low cutting forces

Choosing the right corner radius end mill isn't just about material compatibility or diameter—it’s also about geometry, access, and rigidity. Each of the three types discussed here is tailored for different challenges in the workshop. By understanding their unique strengths, you can extend tool life, reduce breakage, and improve surface quality on every job.

Whether you're cutting deep cavities in a mold, finishing intricate surfaces on a 5-axis machine, or simply roughing a steel block with minimal risk, there’s a corner radius tool built for the task.