Siemens SINUMERIK 840D sl Programming Manual page 292

Tool radius compensation
10.2 Contour approach and retraction (NORM, KONT, KONTC, KONTT)
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Approach/Retraction with KONTC
The contour point is approached/exited with constant curvature. There is no jump in
acceleration at the contour point. The path from the start point to the contour point is
interpolated as a polynomial.
Approach/Retraction with KONTC
The contour point is approached/exited with constant tangent. A jump in the acceleration can
occur at the contour point. The path from the start point to the contour point is interpolated as
a polynomial.
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In both cases (G450/G451), the following approach path is generated:
A straight line is drawn from the uncompensated approach point. This line is a tangent
to a circle with circle radius = tool radius. The center point of the circle is on the starting
point.
Retract:
The same applies to retraction as to approach, but in the reverse order.
Programming Manual, 09/2011, 6FC5398-1BP40-2BA0
Fundamentals