# FANUC Series 16/18/160/180-Model C Machining Center Operators Manual

PROGRAMMING
4. INTERPOLATION FUNCTIONS
B–62764EN/01
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Tool length offset must be specified in the polar coordinate interpolation
cancel mode before G12.1 is specified. It cannot be
specified in the polar coordinate interpolation mode. Furthermore, no
offset values can be changed in the polar coordinate interpolation mode.
A tool offset must be specified before the G12.1 mode is set. No offset
can be changed in the G12.1 mode.
For a block in the G12.1 mode, the program cannot be restarted.
Polar coordinate interpolation converts the tool movement for a figure
programmed in a Cartesian coordinate system to the tool movement in the
rotation axis (C–axis) and the linear axis (X–axis). When the tool moves
closer to the center of the workpiece, the C–axis component of the
feedrate becomes larger and may exceed the maximum cutting feedrate
for the C–axis (set in parameter (No. 1422)), causing an alarm (see the
figure below). To prevent the C–axis component from exceeding the
maximum cutting feedrate for the C–axis, reduce the feedrate specified
with address F or create a program so that the tool (center of the tool when
cutter compensation is applied) does not move close to the center of the
workpiece.
L :Distance (in mm) between the tool center and workpiece center when the tool center is the nearest to the
workpiece center
R :Maximum cutting feedrate (deg/min) of the C axis
Then, a speed specifiable with address F in polar coordinate interpolation can be given by the formula below.
Specify a speed allowed by the formula. The formula provides a theoretical value; in practice, a value slightly
smaller than a theoretical value may need to be used due to a calculation error.
L
1
L
2
L
3
θ3
θ2
θ1
X
Consider lines L1, L2, and L3. X is the distance the tool moves per time unit
at the feedrate specified with address F in the Cartesian coordinate system.
As the tool moves from L1 to L2 to L3, the angle at which the tool moves per
time unit corresponding to X in the Cartesian coordinate system increases
fromθ1 toθ 2 to θ3.
In other words, the C–axis component of the feedrate becomes larger as the
tool moves closer to the center of the workpiece. The C component of the
feedrate may exceed the maximum cutting feedrate for the C–axis because
the tool movement in the Cartesian coordinate system has been converted to
the tool movement for the C–axis and the X–axis.
F < L × R ×
180
π
(mm/min)
WARNING
D Tool length offset
command
D Tool offset command
D Program restart
D Cutting feedrate for the
rotation axis