Siemens SINUMERIK 828D Function Manual page 1528

W1: Tool offset
18.7 Cutting data modification for tools that can be rotated
Shape of cutting edge
If a turning tool turns by an angle against the machining plane (i.e. around an axis in the machining plane,
typically a C axis) that is not a multiple of 180°, then the configuration of the (circular) tool cutting edge in the
machining plane becomes an ellipse. It is assumed that the deviations from the circular form arising on account
of such rotations is so insignificant that they can be ignored (tilt angle < 5°), i.e. the control always ignores the
tool orientation and assumes a circular cutting edge.
This also means that with reference to the active plane, the control accepts only a rotation by 180° as a setting
deviating from the initial position. This limitation is valid for the shape of cutting edge only. The tool lengths are
always considered correctly in random spatial rotations.
Cutting edge position, cut direction and angle
A rotation by 180° around an axis in the machining plane means that while using the tool at the same position,
the spindle rotation direction with reference to the use of the unturned tool must be inverted.
Cut direction and cutting edge position are also not modified like the cutting edge reference point (see below) if
the tool is rotated from the plane by +/- 90° (with a tolerance of app. 1°) because then the configuration of the
cutting edge is not defined in the current plane.
If the tool rotates in the plane (rotation around an axis vertical to the machining place or around the Y axis for
G18), the cutting edge position is determined from the resulting angle for the clearance and holder angles. If
these two angles are not specified for the tool (i.e. $TC_DP10 and $TC_DP24 are both zero), then the new
cutting edge position is determined from the turning angle alone. The cutting edge position changes only in 90°
steps, i.e. the cutting edge position remains independent of the initial state either in the value range 1 to 4 or 5 to
8. The new cutting edge position is then determined exclusively from the angle of rotation if the specified values
for holder angle and clearance angle are not allowed (negative values, resulting plate angle negative or more
than 90°). Clearance angle and holder angle are not modified in all these cases.
Depending on the rotation, the cut direction is modified in such a way that the resulting clearance angle remains
less than 90°. If the original cut direction and the original cutting edge position do not fit together (refer to "Cutting
edge position, cut direction and angle for turning tools"), then the cut direction is not modified during rotation of
the tool.
The angle of rotation in the plane, as it was determined from the tool holder with orientation capacity, is available
in the system variable $P_CUTMOD_ANG or $AC_CUTMOD_ANG. This angle is the original angle without any
final rounding to multiples of 45° or 90°.
Limit cases
If, for a turning tool, the cutting edge position, cut direction , clearance and holder angles have valid values so
that all cutting edge positions (1 to 8) are possible through suitable rotations in the plane, then the cutting edge
positions 1 to 4 are preferred to cutting edge positions 5 to 8 in the cases in which one of the cutting edges (main
or secondary cutting edge) is away from the coordinate axis by less than half the input increment ((0.0005° for an
input specification of 3 decimal digits).
The following is applicable in all other cases (milling tools or turning tools without valid cutting edge parameters)
in which rotation is possible only in 90° steps: If the amount of the rotation angle is smaller than 45° + 0.5 input
increments (corresponds to 45.0005° for an input specification of 3 decimal points), the cutting edge position and
cut direction are not changed, i.e. these cases are treated as rotations that are smaller than 45°. Rotations, the
amount of which deviates from 180° by less than 45° + 0.5 input increments are treated identically as rotations in
the range of 135° to 225°.
Basic Functions
1528
Function Manual, 09/2011, 6FC5397-0BP40-2BA0