Figure 1:  Carbide Chamfer Mills

What is a Chamfer Mill?

The terms chamfer mill, chamfer end mill, and chamfer cutter are synonymous. These specialized milling cutters are designed to create angled cutting surfaces on workpieces, providing a smooth transition between different surfaces or eliminating sharp edges.

What are Chamfer End Mills Made From?

The smaller chamfer cutters (less than or equal to 3/4″) are predominantly made from solid carbide (Figure 1), however there are some cobalt chamfer end mills on the market. The larger diameter chamfer cutters (greater than or equal to 3/4″) mainly use indexable carbide inserts for the cutting edges. An Adjustable Inserted Chamfer Cutter is shown below in Figure 2.  Please note that the smaller diameters may be more productive, because they run at faster revolutions per minute (RPM) than larger diameters given the same surface feet per minute.

Figure 2:  Indexable Carbide Insert Chamfer Cutter

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How Does a Chamfer End Mill Work?

A chamfer end mill works by removing material from the edges of a workpiece at an angle. The cutting edge of the mill is ground to the desired included point angle, typically ranging from 30 degrees to 160 degrees, although custom angles can also be achieved. A 90 degree chamfer end mill will produce a 45 degree chamfer (see Table 1). When the mill rotates, it engages with the workpiece, cutting away material and creating the angled surface.

Table 1:  Chamfer End Mill Included Angle and Resulting Chamfer Angle

Chamferring is the angled removal of metal  from two intersecting surfaces.  Often these surfaces form a 90 degree angle and the chamfer is often at a 45 degree angle as shown in Table 1 .  Beveling is the angled removal of metal  form two parallel surfaces.  Example of these are shown in Figure 3.

Figure 3:  Chamfering and Beveling

Applications of a Chamfer End Mill

Chamfer mills find applications in various industries and machining operations. Here are some common uses of chamfer mills:

1. Deburring: Chamfer cutters are excellent tools for removing burrs or sharp edges left on a workpiece after machining. By chamfering the edges, they create a smooth transition, eliminating any potential hazards or aesthetic imperfections. A 90 degree chamfer end mill is the most common tool for this.
2. Countersinking: Chamfer mills can be used for countersinking a hole, which involves creating a conical recess along the outer edge of the hole. This recess allows screws or fasteners to sit flush with the surface, preventing them from protruding.
3. Edge Breaks: Chamfer end mills are often used to prepare the edges of workpieces for welding or other joining processes. By chamfering the edges, they provide a larger surface area for the weld or adhesive, resulting in stronger and more reliable bonds.
4. Aesthetic Purposes: Chamfer mills can also be used for purely aesthetic purposes. By chamfering the edges of a workpiece, they can add a visually pleasing touch and enhance the overall appearance of the finished product.

Different Chamfer Cutter Designs

There are two primary types of carbide chamfer cutters. The Flat Tip design has a flattened point to give the carbide chamfer cutter strength. The flat tip creates a tip diameter which is generally specified in the tool dimensions. The Pointed Tip design has a gashing that goes close to the center and has a small web. It is designed to get deeper into a hole than a Flat Tip design. Neither of these designs are recommended for drilling, but the Pointed Tip can do some light spot drilling.

Within the above designs there are two additional categories. Historically, most carbide chamfer cutters used a straight cutting edge gashing as shown above.  But there is also a Spiral Tip or Helical Flute design which causes a smoother cutting action with less chatter potential and longer tool performance.  An example is shown below:

Choosing the Right Chamfer Mill

When selecting a chamfer mill, several factors need to be considered:

1. Angle:  The angle of the chamfer mill should be chosen based on the desired chamfer angle specified on the drawing or your preference.  See Table 1 for common chamfer angles and the corresponding chamfer end mill included angles.  Smaller angles create narrower chamfers, while larger angles produce wider chamfers.
2. Length of Cut (LOC):  Choose the right diameter size that has the corresponding LOC long enough to produce the chamfer you need.
3. Design:  Choose between Flat Tip or Pointed Tip, then choose whether to use a straight edge design or a helical flute design, and finally, choose the right diameter size to provide the needed LOC.
4. Material:  Consider the material of the workpiece when choosing a chamfer mill. Different materials require different cutting speeds and feed rates to achieve optimal results. 
5. Coating:  Uncoated mills can be used on all materials, however, AlTiN coated mills should not be used in general on the non-ferrous materials like aluminum, woods, plastics , or brass/bronze.

Final Thoughts

Chamfer mills or chamfer end mills are versatile tools that find applications in a wide range of machining operations. Whether you need to deburr, countersink, prepare edges for welding, or enhance the aesthetics of your workpiece, a chamfer mill can be a valuable addition to your machining arsenal. By understanding how they work and considering the factors mentioned above, you can choose the right chamfer mill for your specific needs.