What is the difference between Machine Zero Vs Work Zero in a CNC router ?

Machine zero is a point in space that has a measure to normally accommodate the machine length and the maximum travel length  along each of the axes.

Work Zero is set normally at the center front of the workpiece.

Below I have shared one diagram of a 2 axis CNC machine whose axes are denoted as X-axis (for traverse path) and Z-axis (for longitudinal path).

The gap between the machine zero and work zero is denoted as the Z-Zero offset (along Z-axis) and the X-Zero offset (along X-axis).

Once if we set these values in Primary zero offset G function G54 and then if we call

G00 X0 Z0, the tool will move to face and center of job at maximum set velocity of the machine (Rapid Traverse)

Table of Contents

Machine Zero

The CNC machine; be it a router or mill or others, utilizes a sequence of numerical commands during any CNC machining  operation. These numeric instructions are sent by the part program in order to maneuver the tool movements along all the axes of the machine. These programs need a point to get started in order to line up both the machining tool and workpiece accurately.

Every CNC machine has an inbuilt position known as the machine zero. This point is specifically at a distant positive direction along all three X, Y, and Z axes. Plus, this machine zero point is unchangeable after the machine (CNC) leaves its patent manufacturer. A work table or CNC machining parts can be fetched to the machine zero point to load and unload the tools.

Work Zero

Before starting a machining task, the work zero position must be fed by the programmer in one way or the other. These ways greatly differ from one CNC machine and its control to another. The earlier method was to assign the work zero position in the program. In this case, the programmer With this method, the programmer informs the CNC control about the distance between the work zero point and the machine’s starting position. This technique is mostly implemented with a G50 (or G92) command, at least at the starting of the  control program and probably at the starting of every tool.

Conversely, the newer and much improved way of assigning the program zero point is through certain offset values. This work zero offset position is termed as fixture offset by the manufacturers of machining-center control, whereas it is called geometry offset by the turning center manufacturers.

So, what exactly does the term offset mean in CNC machining operations? Well, any form of compensation works with offset. Let’s suppose the instance of an electronic calculator offset; it acts like a memory on an electronic calculator. If your calculator has memories embedded within, then they help you store a constant offset value per memory to use during calculations. This saves your time from doing redundant calculations while expediting your other calculations.  

Similarly, the CNC offsets act like the memories on an electronic calculator do. CNC offsets are the storage spaces in the machine control where the numeric values are placed. These offsets can be any value that is frequently required by the machinist during a project, like the degree of adjustment needed to compensate for the tool’s distance to its target. Most CNC machining tools/parts have at least one offset value per tool.

Note: Using an offset value depends on the type of machine tool and  compensation being applied.

There are several prominent reasons for tool offset applications. But, I will keep that for another day. Let’s check out how this offset value helps in work zero positioning. 

CNC machining centers having coordinate system shifting (along called fixture offsets) let you set out the program zero position, while keeping it separate from the program. The turning center manufacturers also allow the program zero assignment with their geometry offset feature.

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