Chapter 4:

Coordinate System

Upon successful completion of this lesson, you will be able to:

• Identify the elements of the Cartesian coordinate system.
• Explain the purpose of the Work Coordinate System (WCS) and considerations for its selection.
• List the major elements of a closed-loop servo control mechanism.
• Identify the location and orientation of the machine coordinate system.
• Explain the purpose of the Fixture Offset XY.
• Explain the purpose of the Tool Length Offset and how to set it using a scrap a 1-2-3 block.
• Explain the purpose of the Fixture Offset Z and how it is set it using a 1-2-3 block and dial indicator.
• Name the two systems of units used in programming CNC machines

Contents

• Cartesian Coordinate System
• Vertical Milling Center Machine Motion
• Work Coordinate System
• Machine and Tool Offsets

Overview

CNC motion is based on the Cartesian coordinate system. A CNC machine cannot be successfully operated without an understanding of the how coordinate systems are defined in CAM and CNC machine and how the systems work together.

This chapter begins with a review of the Cartesian coordinate system and then explains in detail how the coordinate systems between CAM and the CNC machine are related to each other. It also describes how the machine work coordinate system (WCS) is set on the CNC machine so the machine knows where the part is located within the work space.

It concludes with a discussion of tool length and diameter offsets. Length offsets are required to account for different tool lengths (how far a particular tool extends out of the holder). Diameter offsets are the key to highly precise machining where part tolerances can be maintained to an accuracy of .005 inches or less.