Siemens SINUMERIK 828D Function Manual page 1488

W1: Tool offset
18.5 Tool radius compensation 2D (TRC)
Calculation of intersection
When the intersections in blocks with variable compensation value are calculated, the intersection of the offset
curves (tool paths) is always calculated based on the assumption that the compensation value is constant.
If the block with the variable compensation value is the first of the two blocks to be examined in the direction of
travel, then the compensation value at the block end is used for the calculation; the compensation value at the
block start is used otherwise.
Figure 18-33 Intersection calculation with variable compensation value
Restrictions
If during machining on the inside of the circle the compensation radius becomes geater than the programmed
circle radius, then the machining is rejected with the following alarm:
Alarm 10758 "Curvature radius with variable compensation value too small"
Maintain stability of closed contour
If a radius of two circles is increased slightly, a third block may be necessary in order to maintain the stability of
the closed contour. This is the case if two adjacent blocks, which represent two possible intersection points for a
closed contour, are skipped due to the compensation.
A stable closed contour can be achieved by choosing the first intersection point instead of the second.
SD42496 $SC_CUTCOM_CLSD_CONT ≠ 0 (response of TRC for closed contour).
In that case, the second intersection point is always reached, even if the block is skipped. A third block is then not
required.
Basic Functions
1488
Function Manual, 09/2011, 6FC5397-0BP40-2BA0