Siemens SINUMERIK 840D sl Function Manual page 1845

Figure 2-18
KONTT and KONTC compared
The figure below shows the differences in approach/retraction behavior between KONTT and
KONTC. A circle with a radius of 20 mm about the center point at X0 Y-40 is compensated
with a tool with an external radius of 20 mm. The tool center point therefore moves along a
circular path with radius 40 mm. The end point of the approach blocks is at X40 Y30. The
transition between the circular block and the retraction block is at the zero point. Due to the
extended continuity of curvature associated with KONTC, the retraction block first executes a
movement with a negative Y component. This will often be undesired. This response does
not occur with the KONTT retraction block. However, with this block, an acceleration step
change occurs at the block transition.
If the KONTT or KONTC block is the approach block rather than the retraction block, the
contour is exactly the same, but is simply machined in the opposite direction, i.e., the
approach and retraction behavior are symmetrical.
Basic logic functions: Tool Offset (W1)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Approach and retraction with constant curvature during inside machining of a full circle:
3D representation.
Detailed Description
2.4 Tool radius compensation 2D (TRC)
57