Siemens SINUMERIK 828D Programming Manual page 314

Tool radius compensation
10.4 Smooth approach and retraction
Selecting the approach and retraction direction
Use the tool radius compensation (G140, basic setting) to determine the approach and
retraction direction with positive tool radius:
● G41 active → approach from left
● G42 active → approach from right
G141, G142 and G143 provide further approach options.
The G codes are only significant when the approach contour is a quadrant or a semicircle.
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Programming Manual, 07/2010, 6FC5398-1BP40-0BA0
Fundamentals