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

When only a start point and I, J, and K data are given, two types of involute
curves can be created. One type of involute curve extends towards the
base circle, and the other extends away from the base circle. When the
specified end point is closer to the center of the base circle than the start
point, the involute curve extends toward the base circle. In the opposite
case, the involute curve extends away from the base circle.
The cutting feedrate specified in an F code is used as the feedrate for
involute interpolation. The feedrate along the involute curve (feedrate
along the tangent to the involute curve) is controlled to satisfy the
specified feedrate.
As with circular interpolation, the plane to which to apply involute
interpolation can be selected using G17, G18, and G19.
Cutter compensation C can be applied to involute curve machining. As
with linear and circular interpolation, G40, G41, and G42 are used to
specify cutter compensation.
G40 : Cutter compensation cancel
G41 : Cutter compensation left
G42 : Cutter compensation right
Cutter compensation for an involute curve is implemented as described
First, near the start point of an involute curve, an arc with a curvature close
to the curvature of the involute curve is found. Next, an offset intersection
between the arc and the linear line or arc in the previous block is found.
Similarly, an offset intersection is found near the end point. Then, the
involute curve passing through the two points is used as the tool center
In involute interpolation mode, cutter compensation cannot be started or
Tool center path
Start point
Arc with a curvature
closer to the curva-
ture of the involute
curve near the start
End point
Arc with a curvature closer to the
curvature of the involute curve near
the end point
D Choosing from two types
of involute curves
D Feedrate
D Plane selection
D Cutter compensation C

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