Siemens SINUMERIK 840D sl Function Manual page 147

pTCutMod or ptCut- ModS and in system variables $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 places), 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°.
Cutting edge reference point
The cutting edge center point and the cutting edge reference point are defined for turning tools.
The position of these two points relative to each other is defined by the cutting edge position.
The distance of the two points for cutting edge positions 1 to 4 is equal to √2 times the cutting
edge radius; for cutting edge positions 5 to 8 it is equal to 1 times the cutting edge radius. In the
first case, the cutting edge reference point relative to the cutting edge center point lies in the
machining plane on a bisecting line, while in the second case it lies on a coordinate axis.
If your rotate the tool by a random angle around an axis vertical to the machining plane, the the
cutting edge reference point would also rotate if it had a fixed position relative to the tool. The
above-mentioned condition (position on an axis or a bisecting axis) is not fulfilled in most cases.
This is not desirable. Instead, the cutting edge reference point should always be modified in
such a way that the distance vector between cutting edge reference point and cutting edge
center point has one of the mentioned 8 directions. The cutting edge position must be modified
for this if necessary.
The ratios are shown with examples in the figure below:
Tools
Function Manual, 06/2019, A5E47435126B AA
2.9 Modification of the offset data for rotatable tools
W1: Tool offset
147