A milling cutter is a type of cutting tool used in milling machines to remove material from a worked object. These cutters spin at high speeds and remove material in small increments until they reach the final shape. Some styles of milling cutters may double as drill bits, while others are very specific in form and function.
There are a huge number of different milling cutter styles. Even with all the variation, there are a few parts that are the same on nearly every cutter. Nearly all cutters have a shaft that connects to the milling machine. This shaft may be totally smooth or have a specialized shape that allows it to connect more securely to the machine. Most small milling cutters, such as those used in household tools, are smooth so it is easier to exchange bits quickly.
The flute and tooth make up the cutting portion of a milling cutter. A flute is a groove that winds around the cutter, and the tooth is the sharp top edge of the flute. Some milling cutters have one flute, while others have more. When a milling cutter has multiple flutes, they never cross one another and they stay equidistant down the entire shaft. The more flutes a cutter has, the more teeth work the object and the faster it removes material.
While in operation, a milling cutter works though thousands of tiny cuts. The tooth barely touches the worked object and removes a thin sheet of material. Since it does this over and over again as the cutter spins, it amounts to a great deal of removed material. As the material separates from the worked object, the waste material moves up the shaft of the cutter through the flutes.
The shape of the flute as it winds down the shaft is a helix. The helical angle of the milling cutter determines exactly the type of work it is for and what the finish level of its cuts will be. The helical angle uses the shaft as one line and the angle of any flute as the other. A milling cutter with a low angle removes material in large gouges while higher-angle cutters remove extremely small amounts of material. The high-angle cutters are often used as a finisher to put basic polish on a cut.
The design of the milling cutter’s end determines what sort of work it can do. If a cutter has a flat end, it cannot drill down into a material—it has to approach from the side. A cutting end, such as those on a slot drill, allows it to make holes in an object. Lastly, a contoured head, like the one on a ball nose cutter, allows the tip to move across a surface while in operation. This allows for the creation of groves in a shaped surface.