Here we will look into more detail about CNC milling machines. We will start by examining what a milling machine is before we go into CNC milling machines.


Milling is the process by which surface material is removed by rotary cutters. This is done by advancing (or Feeding) the work piece at an angle to the cutting tool. Please see an example of a milling machine below. Other milling machines may have slightly different configurations but the working parts will be more or less the same.

If you replace the manual wheels and levers with servo motors and connect them to a computer you will have yourself the basics of a CNC milling machine.


The main difference is what they cut. A Router is designed to cut softer materials than a milling machine. A router will cut wood, plastic and even softer metals for example aluminium.  Milling machines are designed to cut metal, plain and simple. If you are making metal objects then this is the machine for you.

Another difference would be spin speed or RPM. A router can rotate at about 18,000 RPM. A Milling machine is much slower at around 1,000 rpm’s.

Also a standard router cuts on a set table (There are 5 Axis routers where this may not apply). The router cutting tool will move across the surface of that table in X,Y,Z coordinates. The table in the standard milling machine moves so that the surface of the material is presented to the cutting tool.

Milling machines are for more accurate that routers. Milling machines can cut to within a 1,000th of an inch when cutting metal.


Milling machines were automated with the advent of computers. Automation started around the end of the Second World War and as computing and software developed so did CAM (Computer Aided Manufacturing). This was the use of programs controlling the milling machine.

This made it possible to automate the cutting process and change the configuration from the usual 3 axis Cartesian X,Y,Z to the 5 axis configuration X,Y,Z, A,B . Please see the Diagram below.

This configuration allows the 5 axis milling machine to carve complex shapes with great accuracy. The example above is to give you an idea about the 5 axis configuration so I haven’t included all the parts of the working CNC machine.

I hope that this gives you some idea of what a milling machine is and what it does. I will be reviewing some milling machines in future blogs. Please take a look at other blog content on this site.