User's Manual ISO TNC 360 (260020xx, 280490xx) - heidenhain

1 Introduction
1.2 Fundamentals of NC
Reference system
In order to define positions one needs a reference system. For example,
positions on the earth's surface can be defined "absolutely" by their
geographic coordinates of longitude and latitude. The term "coordinate"
comes from the Latin word for "that which is arranged", i.e. dimensions
used for determining or defining positions. The network of horizontal and
vertical lines around the globe constitutes an "absolute reference system"
– in contrast to the "relative" definition of a position that is referenced, for
example, to some other, known location.
Cartesian coordinate system
On a TNC controlled milling machine a workpiece is normally machined
according to a workpiece-referenced Cartesian coordinate system (a
rectangular coordinate system named after the French mathematician and
philosopher René Descartes, Latin: Renatus Cartesius; 1596 to 1650). The
Cartesian coordinate system is based on three coordinate axes X, Y and Z,
which are parallel to the machine guideways. The figure to the right
illustrates the "right hand rule" for remembering the three axis directions:
the middle finger is pointing in the positive direction of the tool axis from
the workpiece toward the tool (the Z axis), the thumb is pointing in the
positive X direction, and the index finger in the positive Y direction.
TNC 360 1-7
90°
Greenwich
0° 90°
60°
60°
30°
0°
30°
Fig. 1.8: The geographic coordinate system
is an absolute reference system
+Y
+Y
+Z
+X
+Z
+X
Fig. 1.9: Designations and directions of the
axes on a milling machine