1
Introduction
1.2 Fundamentals of NC
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Reference system
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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 constitute an “absolute reference system”
-in contrast to the “relative” definition of a position that is referenced,
for example, to some other, known location.
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Cartesian coordinate system
A workpiece is normally machined on a TNC 370 controlled milling
machine according to a workpiece-reference Cartesian coordinate
system (a rectangular coordinate system named after the French
mathematician and philosopher Fiene Descartes, Latin: Renatus Cartesi-
us; 1596 to 1650). The Cartesian coordinate system is based on three
coordinate axes X, Y and Z, which are parallel to the machine guide-
ways. The figure to the right illustrates the “right hand rule” for remem-
bering 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.
Fig. 1.9: The geographic coordinate system
is an absolute reference system
Fig. 1 .I 0: Designations and directions of the
axes on a milling machine
TNC 370
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