Siemens SINUMERIK 828D Function Manual page 1513

W1: Tool offset
18.6 Toolholder with orientation capability
MD20180
The rotary axis position is used with its programmed or calculated value, when the machine data:
MD20180 $MC_TOCARR_ROT_ANGLE_INCR[i] = 0 (Rotary axis increment of the tool carrier that can be
oriented)
If the machine data is not zero however, the position used is the nearest grid point obtained for a suitable integer
value n from the equation:
φ = $MC_TOCARR_ROT_ANGLE_OFFSET[i] + n * $MC_TOCARR_ROT_ANGLE_INCR[i]
This functionality is required if the rotary axes need to be indexed and cannot, therefore, assume freely-defined
positions (e.g. with Hirth tooth systems). System variable $P_TCANG[i] delivers the approximated valued and
system variable $P_TCDIFF[i] the difference between the exact and the approximated value.
Frame orientation TCOFR
With TCOFR (determination of the angle from the orientation defined by an active frame), the increments are
scaled after determination of the angle from the active frame rotation. If the requested orientation is not possible
due to the machine kinematic, the machining is aborted with an alarm. This also applies if the target orientation is
very close to an achievable orientation. In particular the alarm in such situations cannot be prevented through the
angle approximation.
TCARR frame offset
A frame offset as a result of a toolholder change becomes effective immediately on selection of TCARR=.... A
change in the tool length, on the other hand, only becomes effective immediately if a tool is active.
TCOFR/TCOABS frame rotation
A frame rotation does not take place on activation and a rotation, which is already active, is not changed. As in
case T (only the tool can be rotated), the position of the rotary axes used for the calculation is dependent on the
G code TCOFR / TCOABS and determined from the rotation component of an active frame or from the entries
$TC_CARRn.
Activation of a frame changes the position in the workpiece coordinate system accordingly, without compensating
movement by the machine itself. The ratios are shown in the figure below:
Basic Functions
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Function Manual, 09/2011, 6FC5397-0BP40-2BA0