## Coordinate Systems

The machine tool is positioned by describing sets of coordinates.

In the case of the VMC (Vertical Machining Centre) shown on the left, the coordinate will be described by 3 Axes.

A basic lathe operates by describing positions using 2 axes.

The coordinate system is laid out by identifying the Z axis first. The Z axis is always in line with the main rotating spindle. On the VMC this holds the cutting tool and is vertical; on the lathe this holds the work piece, it is horizontal and inline with the bed.

The X axis is used next and then the Y axis. The Axes for the VMC are shown in the image, the lathe uses just the Z and X axes.

In the case of the VMC (Vertical Machining Centre) shown on the left, the coordinate will be described by 3 Axes.

A basic lathe operates by describing positions using 2 axes.

The coordinate system is laid out by identifying the Z axis first. The Z axis is always in line with the main rotating spindle. On the VMC this holds the cutting tool and is vertical; on the lathe this holds the work piece, it is horizontal and inline with the bed.

The X axis is used next and then the Y axis. The Axes for the VMC are shown in the image, the lathe uses just the Z and X axes.

The coordinate system used in most cases of CNC machining is a rectangular system, the technical name for this being the Cartesian Coordinate System.

When writing coordinates it is standard practise to write them in the order of X, Y, and Z.

When CNC programming the coordinate system must reference from a fixed point; this is called the origin or more commonly in manufacturing, the datum. The datum is the position where X, Y, and Z all equal zero. This is usually a point on the component and this position is usually decided by the manufacturing engineer or CNC programmer.

The coordinate system is almost always an absolute coordinate system. Absolute meaning all coordinates are measured from the datum.

Other coordinate system are found in CNC manufacturing; it is not unusual to find Incremental (Relative) coordinates used on many machines and it is possible to use Polar coordinates on most machines.

Incremental coordinates do not refer back to the original datum, the position of the datum moves with the programmed coordinate. The machine moves towards a programmed position; when it gets to that position the position becomes X0Y0Z0 (the new datum). the next position is described from this new datum.

Polar coordinates can be used in Abs and Inc modes but the coordinate system is not rectangular; the Polar coordinate system is based on a rotating angle and length of radius.

Basic programming - such as the programming used during the 16wk college course uses Cartesian coordinates using Absolute positioning.

When writing coordinates it is standard practise to write them in the order of X, Y, and Z.

When CNC programming the coordinate system must reference from a fixed point; this is called the origin or more commonly in manufacturing, the datum. The datum is the position where X, Y, and Z all equal zero. This is usually a point on the component and this position is usually decided by the manufacturing engineer or CNC programmer.

The coordinate system is almost always an absolute coordinate system. Absolute meaning all coordinates are measured from the datum.

Other coordinate system are found in CNC manufacturing; it is not unusual to find Incremental (Relative) coordinates used on many machines and it is possible to use Polar coordinates on most machines.

Incremental coordinates do not refer back to the original datum, the position of the datum moves with the programmed coordinate. The machine moves towards a programmed position; when it gets to that position the position becomes X0Y0Z0 (the new datum). the next position is described from this new datum.

Polar coordinates can be used in Abs and Inc modes but the coordinate system is not rectangular; the Polar coordinate system is based on a rotating angle and length of radius.

Basic programming - such as the programming used during the 16wk college course uses Cartesian coordinates using Absolute positioning.