Siemens Sinumerik 840D sl Programming Manual page 25

Three-finger rule
The orientation of the coordinate system relative to the machine depends on the machine type.
The axis directions follow the so-called "three-finger rule" of the right hand (according to DIN
66217).
Seen from in front of the machine, the middle finger of the right hand points in the opposite
direction to the infeed of the main spindle. Therefore:
● the thumb points in the +X direction
● the index finger points in the +Y direction
● the middle finger points in the +Z direction
Figure 2-1
Rotary motions around the coordinate axes X, Y and Z are designated A, B and C. If the rotary
motion is in a clockwise direction when looking in the positive direction of the coordinate axis,
the direction of rotation is positive:
Fundamentals
Programming Manual, 01/2015, 6FC5398-1BP40-5BA2
"Three-finger rule"
Fundamental Geometrical Principles
2.4 Coordinate systems
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