Siemens SINUMERIK 840DE Programming Manual page 141

N110 G1 X23.293 Z0 F10
N115 X40 Z-30 F0.2
N120 CT X58.146 Z-42
N125 G1 X70
Description
In the case of splines, the tangential direction is defined by the straight line through the last
two points. This direction is generally not the same as the direction at the end point of the
spline with A and C splines with active ENAT or EAUTO.
The transition of B splines is always tangential, the tangent direction is defined as for A or C
splines and active ETAN.
Frame change
If a frame change takes place between the block defining the tangent and the CT block, the
tangent is also subjected to this change.
Limit case
If the extension of the start tangent runs through the end point, a straight line is produced
instead of a circle (limit case: circle with infinite radius). In this special case, TURN must
either not be programmed or the value must be TURN=0.
Note
When the values tend towards this limit case, circles with an unlimited radius are produced
and machining with TURN unequal 0 is generally aborted with an alarm due to violation of
the software limits.
Position of the circle plane
The position of the circle plane depends on the active plane (G17-G19).
If the tangent of the previous block does not lie in the active plane, its projection in the active
plane is used.
If the start and end points do not have the same position components perpendicular to the
active plane, a helix is produced instead of a circle.
Fundamentals
Programming Manual, 10.2004 Edition, 6FC5 298-7AB00-0BP1
4.11 Circular interpolation with tangential transition (CT)
;Program circle with tangential
;transition
Programming Motion Commands
4-35