CNC Cordinate System
You can think of the coordinate system as how CNC machines understand 3D space. Without a coordinate system, your CNC would have absolutely no way of knowing:
- Where your block of material is
- How far away your tool is from your part
- What movements to use to machine your part
Your CNC Machine’s Origin
Every CNC machine has its own internal origin point called Machine Home. When your CNC first boots up, it has no idea where it is in physical space and requires a calibration to get its bearings.
When this process occurs, all three axes of your CNC move towards their maximum mechanical limit. Once a limit is reached, a signal gets sent to a controller which records the home position for that particular axis. When this occurs for all three axes, the machine is now “homed.”
For example, when your CNC finds its home position, it’s typically at extreme mechanical limitations along the X, Y, and Z axes. Imagine having to use these extreme coordinate values as the starting place for your CNC program. What a nightmare.
To make writing CNC programs easier, we use a different coordinate system designed for human manipulation called a Work Coordinate System, or WCS. The WCS defines a particular origin point on a block of material, usually in CAM software like Fusion 360
A CNC machine will use what’s called a work offset to determine the difference in distance between your WCS and its own home position. These offsets get stored in the controller of the machine, and can typically be accessed in an offset table
Machining multiple parts
Here we can see that several offsets have already been programmed, G54, G55, and G59. What’s the benefit in having multiple offsets? If you are machining multiple parts in one job, each part can be assigned its own offset. This allows the CNC machine to accurately relate its coordinate system to multiple parts in different places, and complete multiple setups at once.
It’s pretty common to use multiple tools for the same job, but you need a way to account for different tool lengths. A tool offset are programmed into your CNC machine to make this easy work. With a tool offset programmed, your CNC machine will know exactly how far each tool extends from the spindle