CNC machines work by using a rotating cutting tool to cut and carve materials. Different cutting tools are used for different types of projects and applications. They can vary in size, shape, material, and design.
There are lots of different names for cutting tools that are used for CNC. End mill, bit, or cutting tool are all terms that are used in describing the cutting tools used on a CNC.
As a CNC operator, you will learn to choose the correct end mill for the job and use the correct speeds and feeds in your CAM program to get the best results in your project. We will discuss how we do this in this guide.
Cutting tool lingo
We can identify end mills based on several different features. Here are some of the basic terms you should know.
Tool length: Describes the overall tool length of your end mill. Depending on how thick your material is and how deep you want to cut, you can vary the length of your end mill. As a general rule of thumb, it is best to use the shortest tool possible for your application.
Shank length: Describes the length of the smooth part of the area which your router or spindle collet will grip. We refer to this part of the end mill as the “shank”.
Cutting length/Cutter length: Describes the length of the actual cutting area of the end mill. You can use the whole length of this part of the end mill to cut your material.
Shank diameter: Describes the diameter of the shank. This measurement is important to ensure that your end mill will fit into your router or spindle. With most routers, you will typically use a 1/4″ shank, or use a 1/4″ to 1/8″ collet adapter to allow for use of 1/8″ shank end mills.
Flutes/Flute count: End mills can have one, two, three or more flutes. You will choose end mills with different flute counts based on the material and speed of cutting you choose to do.
Cutting diameter: Describes the diameter of the cutting portion of the tool. When you cut a slot into a material, the width of the cut will be determined by the cutting tool. A cutter with a smaller diameter will allow you to reproduce smaller details, with the trade-off of having a lower material removal rate (takes longer to cut something)
End mills also have different shape tips for different types of projects, and each shape has their strengths and weaknesses. We will discuss these three common shapes.
Ball nose: We refer to the rounded shape of this type of end mill as a “ball nose”. Ball nose end mills are great for 3D type and relief carving, such as for cutting waves and curves on the surface of the material. However, ball end mills are not great for 2D or flat surfaces, since they can leave a “scalloped” look to the surface.
Flat end: This type of end mill simply has a flat tip. This type of end mill is the most common and is great for cutting 2D objects.
V-bit: V-bits have an angled tip that works great for engraving, and comes in varying angles and sizes. You can do a simple engraving by running the tip against a material, or you can do something called “v-engraving” or “v-carving” which automatically varies the height of the bit as it cuts to change the width of the engraving.