Siemens SINUMERIK 828D Function Manual page 204

B1: Continuous­path Mode, Exact Stop, LookAhead
3.6 Contour/Orientation tolerance
Programming does not trigger a preprocessing stop. If possible, it does not interrupt NC block compression
either.
The programmed values are valid until they are reprogrammed or deleted by being written with a negative value.
They are also deleted at the end of a program, in the event of a channel reset, a mode group reset, an NCK reset
(warm restart), and POWER ON (cold restart). On deletion of these values, the values from the machine and
setting data are restored.
New values can be programmed and become effective in any block.
Note
The programmed tolerance also acts upon functions which are only implicitly dependent
upon the tolerance. These are currently:
• Limiting the chord error in the setpoint value calculation
• The basic functions of the free-form surface mode
Note
The following rounding functions are not affected by the programming of CTOL, OTOL, and
ATOL:
• rounding orientation with OSD
Reason: OSD does not use a tolerance, it uses a distance from the block transition.
• Rounding with G644
Reason: G644 is not used for processing, it is used for optimizing tool changes and other
movements in air.
• Rounding block transitions with uniform tangents and non-uniform curvature with G645
G645 virtually always behaves like G642 and, thus, uses the programmed tolerances.
The tolerance value from machine data MD33120 $MA_PATH_TRANS_POS_TOL is only
used in uniformly tangential block transitions with a jump in curvature, e.g. a tangential
circle/straight line transition. The rounding path at these points may also be located
outside the programmed contour, where many applications are less tolerant.
Furthermore, it generally takes a small, fixed tolerance to compensate for the sort of
changes in curvature which need not concern the NC programmer.
Read tolerance values
For more advanced applications or for diagnostics, the currently valid tolerances for the compressor functions
(COMPON, COMPCURV, COMPCAD), the smoothing types G642, G643, G645, OST, and the orientation
smoothing ORISON can be read via system variables irrespective of how they might have come about.
• For the display in the user interface, in synchronized actions or with a preprocessing stop in the part program
via the system variables:
204
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
Basic Functions