Siemens sinumerik 840D sl Operating Manual page 394

Programming technology functions (cycles)
8.5 Contour milling
Parameters Description
CP Positioning angle for machining area
- (only for ShopTurn, machining surface, face Y)
C0 Positioning angle for machining surface
- (only for ShopTurn, machining surface, peripheral surface Y)
Reference point Z or X
Z0 or - (only for G code and ShopTurn, machining surface, face C/Y) or
X0 - (only for ShopTurn, machining surface, peripheral surface C/Y)
Final drilling depth (abs) or final drilling depth referred to Z0 or X0 (inc)
Z1 or - (only for C code and ShopTurn, machining surface, face Y/C) or
X1 - (only for ShopTurn, machining surface, peripheral surface Y/C)
Maximum depth infeed - (only for machining ∇ and ∇∇∇)
DZ or - (only for G code and ShopTurn, machining surface, face C/Y) or
DX - (only for ShopTurn, machining surface, peripheral surface C/Y)
Depth finishing allowance - (only for machining ∇)
UZ or - (only for G code and ShopTurn, machining surface, face C/Y) or
UX - (only for ShopTurn, machining surface, peripheral surface C/Y)
Finishing allowance, plane
UXY or - (only for G code and ShopTurn, machining surface, face C/Y) or
UYZ - finishing allowance plane - (only for ShopTurn, machining surface, peripheral surface
C/Y)
Approach Planar approach mode:
Quadrant:

Part of a spiral (only with path milling left and right of the contour)
Semi-circle:

Part of a spiral (only with path milling left and right of the contour)
Straight line:

Slope in space
Perpendicular:

Perpendicular to the path (only with path milling on the center-point path)
axis-by-axis - (only for "quadrant, semi-circle or straight line" approach)
Approach strategy 
spatial - (only for "quadrant, semi-circle or straight line" approach)

R1 Approach radius - (only for "quadrant or semi-circle" approach)
L1 Approach distance - (only for "straight line" approach)
FZ Depth infeed rate
Retraction Planar retraction mode:
Quadrant:

Part of a spiral (only with path milling left and right of the contour)
Semi-circle:

Part of a spiral (only with path milling left and right of the contour)
Straight line:

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Operating Manual, 07/2010, 6FC5398-8CP40-0BA0
Unit
Degrees
Degrees
mm
mm
mm
mm
mm
mm
mm
mm
Turning