Siemens SINUMERIK 840DE Programming Manual page 332

Tool offsets
8.9 Contour approach and retraction (NORM, KONT, KONTC, KONTT)
Travel round contour at starting point, G41, G42, KONT
Two cases are distinguished here:
1. Starting point lies in front of the contour
The approach strategy is the same as with NORM.
The path tangent at the starting point serves as a dividing line between the front and rear of
the contour.
1. Starting point lies behind the contour
The tool travels round the starting point either along a circular path or over the intersection of
the equidistant paths depending on the programmed corner behavior G450/G451.
The commands G450/G451 apply to the transition from the current block to the next block.
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Programming Manual, 10.2004 Edition, 6FC5 298-7AB00-0BP1
Fundamentals