Corner Radius End Mill Guide

What are Corner Radius End Mill?

An end milling is a type of cutting tool used in industrial milling applications. They have been divided into several broad categories based on their number of flutes, helix angle, material, and coating material. Each category is then further divided into specific types of end mills by applications and geometry. Today we are going to specifically look at a specific type of end mill – the corner radius end mill.

Corner radius end mills have a unique square nose with rounded corner that is able to ensure the longevity of the end mill by distributing cutting force evenly to prevent damage. Corner radius end mills are sometimes referred to as the bull nose end mills as well, which rotate against a work piece to create a flat-bottomed groove with slightly rounded corners for milling applications wherein a specific radius is required. Corner radius end mills are typically used on manual or CNC milling machines.

Factors for Selecting a Corner Radius End Mill

There are several factors that you should consider when choosing your corner radius end mill. Choosing the right tool can lead to the extended life of the tool; Choosing the wrong one could cause inaccuracy and unfavorable machining experience.

Choosing the right pilot diameter: The pilot diameter of a corner radius end mill dictates the tool’s limitations. When pilot diameters are greater, the tool can be run at lower speed. And when the pilot diameters are smaller, the tool can be run at a faster speed thanks to the larger effective cutter radius. Therefore, you would need to first determine the effective cutter diameter. Larger diameters also offer more rigidity than smaller pilot diameters because of the added material behind the radius. But smaller pilot may still be useful for working with narrow holes or slots. Smaller pilots enable tighter turns when operating an inside corner as well.

Flared or Unflared: It is generally not advisable to put a full radius on a part because it could potentially leave an over-cut on the work piece. This is especially prone to happen if the tool is not dialed in completely, or when there is minor vibration and runout. A slight 5-degree flare on the pilot and shoulder should complement the radius perfectly on the work piece, preventing over-cuts on the work piece. A flared corner radius end mill can lead to incomplete radius, but allows for more forgiveness at the same time. Furthermore, a clean surface finish can be left on the work piece using this tool without requiring a second finishing operation to clean leftover marks. An unflared corner radius end mill, on the other hand, leaves a complete radius on the work piece, but more set-up time is usually needed to ensure it’s stepless.

Front or Back: You typically have a choice between front corner radius end mill and a back corner radius end mill depending on the location of the part you are machining. A back corner radius end mill should be used to put a radius on an area of the part facing the opposite direction of the spindle. On the other hand, a front corner radius end mill can lead to increased cycle times because the material can be rotated. Make sure that you have appropriate clearance for the head diameter with the proper reach length if a black corner radius end mill is to be used. The work piece will require adjustment if there isn’t enough clearance.

Flute Count: Corner radius end mills typically come in 2, 3 and 4 flute styles. 2 flute corner radius end mills are generally used for aluminum and non-ferrous materials. The 3 flutes style has become increasingly popular because of its softer nature which allows longer tool life. And when machining steels, 4 flutes style should be used in order to extend tool life by distributing the wear over multiple teeth. 4 flutes corner radius end mills are also capable of running at higher feeds as opposed to the other styles.

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