Currently CNC machines are found almost everywhere, from the small workshops of the great machining manufacturing companies.
There are almost no manufacturing products that are not somehow related to the technology of these machines. All workers should be aware of the industries that you can do with these technological marvels.

In this article, we explore the fundamentals of CNC, showing much of what is involved in using these sophisticated machines. For readers who work directly with any or CNC machines, will be shown the basics of each one of the main functions of the CNC. At the end of this presentation, you should have learned a how and why the CNC machine works, and understand how to do these things you need to know to work relatively well with any type of CNC machine.
One of the advantages of CNC machines and these machines can run unattended for a human entire machining cycle, allowing the operator time to perform other tasks. This reduces operator fatigue, fewer mistakes caused by human error, machining and consistent and predictable time for each product. Since the machine will be running under program control, the level of skill required of the CNC operator is also reduced when compared to a conventional machine tool operator. Another advantage is the incredible accuracy of the specifications as well as playback. This means that once a program is tested and approved, can be produced two, ten, or a thousand identical products easily with precision and consistency.

Fundamentals of CNC, Motion Control - The Heart of CNC:

Figure 1. The movement of a conventional desktop machine is triggered by the operator that turns a crank. The precise positioning is performed by the operator that counts the number of laps to be placed on the handle with graduations on the dial (scale ring) thus depend exclusively on the skill of the operator.

The most basic function of any CNC machine is motion control automatic, accurate, and consistent. All CNC equipment has two or more directions of motion, called axes. These axes can be precisely and automatically positioned along their lengths of travel. The two most common axis types are linear (driven along a straight path) and rotary (driven along a circular path).
Instead of turning cranks to be moved manually as is done in conventional machine tools, CNC machines have moved their axes controlled by CNC servo motors, and guided by the part program.
In general, the movements are programmable in almost all CNC machine tools. Figure 1 (above) shows the control of movement of a conventional machine. Figure 2 (below) shows a linear motion axis of a CNC machine.

Figure 2. A CNC machine receives the commanded position of the CNC program. The servo motor is driven by the number of turns in the corresponding zone of steel balls at a speed appropriate to place the table where he was led along a linear axis. A feedback device confirms that the amount of ball screw revolutions took place.
A CNC command executed within the control (usually by a program) tells the drive motor to rotate a precise number of times. The rotation of the servo motor rotates the spindle is in a support table is mounted on the bus, when the spindle rotates the grooves of the same forces the table in one direction and it slides on the bus support generating movement in one direction.

Understanding coordinate systems: It is inconceivable for the user to generate CNC axis movement trying to control the servo motor of each axis. Instead, all CNC controls allow axis motion control in a much simpler and more logical to use a coordinate system. The two coordinate systems of the most popular CNC machines are used in the coordinate system Cartesian or rectangular coordinate (most used) and the polar coordinate system. A very common application for the rectangular coordinate system is the graphics.
We take what we now know about graphics and relate to the movement axis of the CNC. Instead of plotting theoretical points to represent conceptual ideas, the CNC programmer plot the physical end points for each axis movement. Each linear axis machine tool can be thought of as a base line of the graph. As the graph base lines, the axes are divided into measurable increments in mm (measured distance). In order of inches, the smaller increment may be 0.0001 inch. Metric mode, the smaller increment may be 0001 mm. Just like the graph, each axis in the coordinate system of the CNC machine has to start somewhere. This place where the basic vertical and horizontal lines meet is called the point of origin of the graph.

Figure 4 shows how the movements are controlled commonly axis CNC machines. For example, the two axes that we're showing are called X and Y, but remember that the zero in the program can be applied to any axis. Although the name of each axis will change from one type of CNC machine, this example should be used to show it and the axis motion can be controlled.

As you can see, the lowest position in the corner and the leftmost part number will correspond to the zero position for each axis. Before writing the program, the programmer must determine the zero position. Typically, the program zero point is chosen as the point where all dimensions are begun.
With this technique, if the programmer wants to return the tool to a position 10 mm to the right of the zero point of the program is run X10.0. If the programmer wishes the tool to move to a position 10 mm on the zero point of the program is run Y10.0.
With the examples given, all points happened to be up and right of the zero point of the program. This area, above and right of the zero point of the program is called a quadrant (in this case, a quadrant number). Figure 5 shows the relationship of the four quadrants as well as representations "more and less" than required for each.

Figure 5. If a dot appears on any CNC program in a different quadrant of the first quadrant, a minus sign should be placed in at least one of its axes.

Absolute x incremental: In the absolute mode, the coordinates of the points of all motions will be specified from the zero point of the program. For beginners, this is usually the best and easiest method to specify the locations for motion commands. But there is another way of specifying the axis motion. The incremental mode is specified where the movements from the current position of the tool. But the times are so rare that this method is useful at the moment is becoming a thing of the past, because it is uncomfortable and difficult.And important to take great care in making the motion commands.

Incremental motion x absolute motion :

Figure 6. It is very easy to tell the precise location of the tool in any command given by the absolute mode. In incremental mode, can be very difficult to determine the current position of the tool for a given motion command.

CNC programs: Almost all CNC controls currently use a single word address format for programming. (The only exceptions to this are certain conversational controls). Through this address format word, we mean that the CNC program is made ​​up of sentence commands. Each command is composed of CNC words and each have your e-letters and numeric values. The letter address (X, Y, Z, etc..) Tells the control the kind of word and numerical value tells the control the value of the word. Used as words and sentences in Portuguese words on a CNC CNC machines say what we want to do with this control block. 

As already stated, programs are composed of commands and commands are composed of words. Each word has a letter address and a numeric value. The letter address said to control the type of word. The CNC control manufacturers vary with respect to how they determine the names of the words (lyrics and direction) and their meanings. In the beginning the CNC programmer must reference the manufacturer's manual to determine how the control should be the names and meanings of each word. Here is a brief list of some of the word types and specifications address common letter.
O - Number of Program (Used for program identification)
N - Sequence number (used for line identification)
G - Preparatory function
X - X axis
Y - Y axis
Z - Z axis
R - Radius
F - Feedrate
S - Spindle
H - tool length compensation.
D - Tool radius compensation.
T - Tool
M - Miscellaneous function
As you can see, many of the letter addresses are chosen in a logical way (for tool T, S zone, F for feed rate, etc.).. Some require memorizing.
There are two letters (G and M) that let you assign special functions. The preparatory function (G) is specifically used to set modes of the machine. We have introduced absolute mode is specified by G90 and G91 incremental mode specified by. These are but two of the preparatory functions used. You must reference the manual control of the manufacturer to find the list of G and M functions of your machine.
As the preparatory functions, the miscellaneous functions (M) allow a variety of special functions. Miscellaneous functions are typically used as programmable switches (such as the spindle on and off, on and off the drink, and so on). These functions are also used to allow programming of many functions of the CNC machine tool.

Programming of the decimal point : Some letters of CNC programs allow the specification of real numbers (numbers that require portions of a whole number). Examples include the X axis (X), Y (Y) and radius (R). Almost all current models of CNC controls allow you to use a decimal point in the specification of each letter address. For example, X3.0625 can be used to specify a position along the axis X.
On the other hand, some letter addresses are used to specify integers. Examples include: the tool number (T), succession of the numbers of blocks (N), preparatory functions (G), and miscellaneous functions (M). For these types, most controls do not allow you to use a decimal point.

Other programmable functions : All CNC machines are simpler functions different programmable axis motion. With the explosion of CNC equipment of today, almost everything about the machine is programmable. The list of programmable functions can vary dramatically from one machine to another, and the user must learn these functions are programmable for each CNC machine to do a program.