The CNC Mill
The CNC mill is an amazing machine tool capable of manufacturing virtually any part you can imagine. If you have the CNC software to program it and the skill level to process it, the mill can do the rest. A standard CNC mill consists of 3 axes. The X axis allows travel from left to right. The Y axis allows travel from back to front. The Z axis allows travel up and down and is the axis where the spindle is located. There are more advanced CNC mills that can have up to 5 axes, but X, Y and Z are standard on all CNC mills. The other two axes are A and B. A is the 4th axis and allows rotation clockwise and counter clockwise in the horizontal plane (rotating about the X axis). On a CNC mill that has only the standard X, Y and Z axes, the A axis is nothing more than a rotary indexer that is mounted to the table on the mill. This is a reference diagram of what the inside of a CNC mill with a 4th axis looks like.
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B is the 5th axis and allows rotation clockwise and counterclockwise in the vertical plane. This website is a powerful teaching tool that will eventually teach you how to master a CNC machine with all 5 axes! The acronym CNC stands for Computer Numerical Control. CNC mills are controlled by computer generated G-Code. A programmer uses CAM software to generate a series of numbers and letters know as G-Code. They then input that data into the machine and it reads and understands it and then executes the appropriate commands. CAM stands for Computer Aided Manufacturing. There are many different types of CAM software, but the one you will learn to master using this site is called Surfcam. You can also manually input data into the machine to edit existing programs or to get the machine to do specific commands. CNC mills vary in size and capacity. They range from small, very compact machines (commonly referred to as mini-mills), to very large, bulky machines capable of manufacturing things like aircraft wings. There are many different sizes and styles depending on what type of part or application it will be used for. The process of milling operates on the principle of rotary motion. That is, a milling cutter or CNC tool is spun about an axis while a workpiece or part is advanced into it in such a way that the sharp edges of the cutter are able to cut chips off of the material with each pass. The rate of speed that the workpiece advances into the cutter is called the feed rate. On a CNC mill, it is most often measured in length of material traveled per each minute that passes. For example, a feed rate of 20 inches per minute means that the cutter travels a distance of 20 inches in one minute. It can also be measured in length of material per full revolution of the cutter. If the feed rate is .002 inches per revolution, that means that the cutter travels a distance of two thousandths of an inch every time it makes a full revolution. The proper feed rate differs greatly depending on several different factors. Type of material, diameter of the cutter, depth of cut and step over amount are all factors that must be considered in order to obtain the correct feed rate for each cutter. It is almost always different for each tool and material so it is extremely important to calculate this accurately to hold close tolerances and get the longest possible tool life. The formulas for calculating feed rates for milling are provided on our downloadable drill chart you can find in our Download section. I sincerely hope you enjoy your journey of learning the CNC mill. It is an amazing machine tool and this program will teach you how to use it efficiently and build parts you can take pride in and be proud of.