HEIDENHAIN TNC 620 User Manual page 295

Testing and running | Running CAM programs
Further adaptations
Take the following points into account with CAM programming:
For slow machining feed rates or contours with large radii, define
the chord error to be only one-third to one-fifth of tolerance T in
Cycle 32. Additionally, define the maximum permissible point
spacing to be between 0.25 mm and 0.5 mm. The geometry error
or model error should also be specified to be very small (max.
1 µm).
Even at higher machining feed rates, point spacings of greater
than 2.5 mm are not recommended for curved contour areas
For straight contour elements, one NC point at the beginning of
a line and one NC point at the end suffice. Avoid the output of
intermediate positions
In programs with five axes moving simultaneously, avoid large
changes in the ratio of path lengths in linear and rotational
blocks. Otherwise large reductions in the feed rate could result at
the tool reference point (TCP)
The feed-rate limitation for compensating movements (e.g. via
M128 F...) should be used only in exceptional cases. The feed-
rate limitation for compensating movements can cause large
reductions in the feed rate at the tool reference point (TCP).
NC programs for 5-axis simultaneous machining with spherical
cutters should preferably be output for the center of the sphere.
The NC data are then generally more uniform. In Cycle 32,
you can additionally set a higher rotary axis tolerance TA (e.g.,
between 1° and 3°) for an even more constant feed-rate curve at
the tool center point (TCP).
For NC programs for 5-axis simultaneous machining with toroid
cutters or spherical cutters, where the NC output is for the south
pole of the sphere, choose a lower rotary axis tolerance. 0.1°
is a typical value. However, the maximum permissible contour
damage is the decisive factor for the rotational axis tolerance.
This contour damage depends on the possible tool tilting, tool
radius and engagement depth of the tool.
With 5-axis hobbing with an end mill, you can calculate the
maximum possible contour damage T directly from the cutter
engagement length L and permissible contour tolerance TA:
T ~ K x L x TA with K = 0.0175 [1/°]
Example: L = 10 mm, TA = 0.1°: T = 0.0175 mm
HEIDENHAIN | TNC 620 | User's Manual for Setup, Testing and Running NC Programs | 01/2022
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