Siemens SINUMERIK 840Di sl Programming Manual page 359

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.
Fundamentals
Programming Manual, 11/2006, 6FC5398-1BP10-2BA0
8.9 Contour approach and retraction (NORM, KONT, KONTC, KONTT)
Tool offsets
359