Programming Systems | CNCAbsolute Programming System programming Basics | G-Code | M-Code | Incremental and

Two types of programming modes, the incremental system and the absolute system, are used for CNC. Both systems have applications in CNC programming, and no system is either right or wrong all the time. Most controls on machine tools today are capable of handling either incremental or absolute programming.

 

Incremental program locations are always given as the distance and direction from the immediately preceding point

• A “X plus” (X+) command will cause the cutting tool to be located to the right of the last point.
• A “X minus” (X-) command will cause the cutting tool to be located to the left of the last point.
• A “Y plus” (Y+) command will cause the cutting tool to be located toward the column.
• A “Y minus” (Y-) will cause the cutting tool to be located away from the column.
• A “Z plus” (Z+) command will cause the cutting tool or spindle to move up or away from the workpiece.
• A “Z minus” (Z-) moves the cutting tool down or into the workpiece.

In incremental programming, the G91 command indicates to the computer and MCU (Machine Control Unit) that programming is in the incremental mode.

Absolute program locations are always given from a single fixed zero or origin point. The zero or origin point may be a position on the machine table, such as the corner of the worktable or at any specific point on the workpiece. In absolute dimensioning and programming, each point or location on the workpiece is given as a certain distance from the zero or reference point.

• A “X plus” (X+) command will cause the cutting tool to be located to the right of the zero or origin point.
• A “X minus” (X-) command will cause the cutting tool to be located to the left of the zero or origin point.
• A “Y plus” (Y+) command will cause the cutting tool to be located toward the column.
• A “Y minus” (Y-) command will cause the cutting tool to be located away from the column.

In absolute programming, the G90 command indicates to the computer and MCU that the programming is in the absolute mode.

The term numerical control is a widely accepted and commonly used term in the machine tool industry. Numerical control (NC) enables an operator to communicate with machine tools through a series of numbers and symbols.

NC which quickly became Computer Numerical Control (CNC) has brought tremendous changes to the metalworking industry. New machine tools in CNC have enabled industry to consistently produce parts to accuracies undreamed of only a few years ago. The same part can be reproduced to the same degree of accuracy any number of times if the CNC program has been properly prepared and the computer properly programmed. The operating commands which control the machine tool are executed automatically with amazing speed, accuracy, efficiency, and repeatability.

The ever-increasing use of CNC in industry has created a need for personnel who are knowledgeable about and capable of preparing the programs which guide the machine tools to produce parts to the required shape and accuracy. With this in mind, the authors have prepared this textbook to take the mystery out of CNC – to put it into a logical sequence and express it in simple language that everyone can understand.

 

Milling Machine

The milling machine has always been one of the most versatile machine tools used in industry (Fig. 5). Operations such as milling, contouring, gear cutting, drilling, boring, and reaming are only a few of the many operations which can be performed on a milling machine. The milling machine can be programmed on three axes:
• The X axis controls the table movement left or right.
• The Y axis controls the table movement toward or away from the column.
• The Z axis controls the vertical (up or down) movement of the knee or spindle.

The main axes of a vertical machining center.