Siemens Sinumerik 840D sl Programming Manual page 23

Reference points
Zero points and reference points for turning
Zero points for milling
Fundamentals
Programming Manual, 01/2015, 6FC5398-1BP40-5BA2
R Reference point
Position defined by output cam and measuring system. The distance to the machine
zero M must be known so that the axis position at this point can be set exactly to this
value.
B Starting point
Can be defined by the program. The first machining tool starts here.
T Toolholder reference point
Is on the toolholder. By entering the tool lengths, the control calculates the distance
between the tool tip and the toolholder reference point.
N Tool change point
Fundamental Geometrical Principles
2.3 Zero points and reference points
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