Milling cutters are rotating cutting tools that are used mainly in milling machines and machining centers.  They remove material via movement within the machine, or directly via their own cutting action. Some milling cutters can drill straight down into the material, while others are capable of 45-degree cuts. Cutting tools for roughing and finishing operations are also available.

How Milling Cutters Work

Milling cutters have one or more teeth, with four-tooth cutters being the most common configuration.  As the teeth cut the material, the rotation of the milling bit sends chips up the flute, the part of the milling cutter with deep helical grooves.  Typically, there is one tooth per flute; however, some products have two teeth per flute. Milling flutes are usually helical to allow the teeth to enter the material gradually, without an excessive amount of vibration.

Types of Milling Cutters

Although there are many different types of milling cutters, common configurations include end mills, face mills, and shell mills.

• End mills are usually mounted vertically and have two or more helical flutes.  Typically, these tools are configured to cut with their ends and on their sides.
• Face mills are used to cut with the ends of the cutter instead of with its sides. The term "face" refers to the creation of a flat face on the workpiece.  Face mills often have a larger diameter than the width of the workpiece to face, so that the work surface can be processed in one pass. 
• Shell mills are a larger type of face mill or end mill that mounts onto an arbor, rather than having an integral shank.  Typically there is a hollow or recess in the center of the shell mill for mounting hardware onto a separate arbor or shank.

The GlobalSpec SpecSearch database also contains information about many other types of milling cutters. These include plunge, thread, and button mills; single-angle and double-angle cutters; and gear hobs.  Some cutting tools are designed to produce a smooth radius, convex or concave features, or helical forms. 

Cutter Configuration, Geometry, and Size

Milling cutters feature either solid construction or a holder-and-insert design. Their tips or end geometry may be square, ball nose, radius tip, or chamfer tip.  Dimensional measurements to consider when selecting milling cutters are the cutting diameter and shank or arbor diameter (if different), as well as the overall length and the cutting (flute) length. Depending on the cutting tool’s design and the buyer’s applications requirements, radius dimension and chamfer or angle may also represent important selection criteria.       

References

Michigan Tech - Milling Page