1 Introduction
V
1.2 Fundamentals of NC
Additional axes
Die TNCs can control the machine in more than three axis. The axes U,
V and W are secondary linear axes parallel to the main axes X, Y and Z,
respectively (see illustration). Rotary axes are also possible. They are
designated as A. B and C.
F
Polar coordinates
The Cartesian coordinate system is especially
useful for parts whose dimensions are mutually
perpendicular. But when workpieces contain
circular arcs, or when dimensions are given in
degrees, it is often easier to use polar coordi-
nates. While Cartesian coordinates are three-
dimensional and can describe points in space,
polar coordinates are two dimensional and can
describe points only in a plane. Polar coordinates
have their datum at a circle center (CC), or pole,
from which a position is measured in terms of its
distance from that pole and the angle of the line
from the pole.
You could think of polar coordinates as the result
of a measurement using a scale whose zero point
is fixed at the datum and which you can rotate to
different angles in the plane around the pole.
Positions in this plane are defined by:
l
Polar Radius PR - The distance from the
circle center (CC) to the defined position.
l
Polar Angle PA - The angle between the
reference axis and the scale.
ig. 1 .I 1: Directions and designations of
additional axes
10
0”
X
Fig. 1.12: Positions on an arc with polar coordinates
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TNC 370
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