As February is quickly coming to a close, we are ramping up into beginning a busy Quarter 2! Of course, before then, our team wanted to sit down and take a little bit of time to help you, our faithful CNC community, by diving into the process of using a G54 Offset. You can also follow along with us in Autodesk’s Fundamentals of CNC Machining textbook on our website. Click here to view it.

Coordinate Systems and Offsets 

Coordinate systems are used in every CNC machine; but be advised that not all machines operate the same, so please consult your manual for proper instructions.

The Cartesian Coordinate System can be thought of as three number lines (or axes), labeled as X, Y, and Z, that are orientated in planes at 90-degrees to one another. The common location where all three axes intersect is called the origin or datum. A pair of any two axes, XY, YZ, and XZ, form a plane. These planes are named by the axes that define them, and each plane can be further divided into quadrants – which are primarily used for defining movement within CNC machines.

Coordinate Systems are used to aid in understanding and defining how machines interpret programmed movement. Both of these topics are discussed in the following sections below.

Figure 1: Cartesian Coordinate System

Figure 2: Quadrants in the XY Plane. Note how coordinates within the quadrants are defined (+/-).

What is a G54 Work Offset?

Work offsets are data registers in the CNC control that hold the distance from the machine home X, Y, Z position to the part datum. These offsets can be thought of like a table on the control:

Figure 3: Work Offsets

The X and Y values represent the distance from the machine home to part datum XY. The Z value is the distance from the tool reference point (for example, the top of a 1-2-3 block) and the part Z-datum. The process for finding tool length offset (TLO) and fixture offset Z is detailed in Lesson 6, CNC Operation.

An example in code:

G54 X0. Y0.

G54 holds the datum’s distance in relations with the tip of the tool. These work offsets are registered into the machine to hold the distance from the X, Y, Z position to part of the datum.