HEIDENHAIN TNC 640 User Manual page 491

Miscellaneous Functions | Miscellaneous functions for path behavior
Calculating the radius-compensated path in advance
(LOOK AHEAD): M120
Standard behavior
If the tool radius is larger than the contour step that needs to
be machined with radius compensation, the control interrupts
program run and generates an error message. M97 inhibits the
error message, but this results in dwell marks and will also move
the corner.
Further information: "Machining small contour steps: M97",
page 486
The control might damage the contour in case of undercuts.
Behavior with M120
The control checks radius-compensated contours for undercuts and
tool path intersections, and calculates the tool path in advance from
the current block. Areas of the contour that would be damaged
by the tool will not be machined (shown darker in the figure). You
can also use M120 to calculate the tool radius compensation for
digitized data or data created on an external programming system.
This means that deviations from the theoretical tool radius can be
compensated.
The number of blocks (99 max.) calculated in advance, can be
defined with LA (Look Ahead) following M120. Note that the larger
the number of blocks you choose, the higher the block processing
time will be.
Input
If you enter M120 in a positioning block, the control continues the
dialog for this block by prompting you for the number of LA blocks
to be calculated in advance.
Effect
M120 must be included in an NC block that also contains an RL or
RR radius compensation. M120 is then effective from this block
until
radius compensation is canceled with R0
M120 LA0 is programmed
M120 is programmed without LA
another program is called with PGM CALL
the working plane is tilted with Cycle 19 or with the PLANE
function
M120 becomes effective at the start of the block.
HEIDENHAIN | TNC 640 | Conversational Programming User's Manual | 10/2017
11
491