HEIDENHAIN TNC 320 User Manual page 232

Cutting motion
The starting point, and therefore the milling direction, is selectable
because the TNC always moves from point
movement from point 1 / 2 to point
any corner of the surface to be machined.
If you are using an end mill for the machining operation, you can
optimize the surface finish in the following ways:
A shaping cut (spindle axis coordinate of point
spindle-axis coordinate of point 2) for slightly inclined surfaces.
A drawing cut (spindle axis coordinate of point
spindle-axis coordinate of point 2) for steep surfaces.
When milling twisted surfaces, program the main cutting direction
(from point 1 to point 2) parallel to the direction of the steeper
inclination.
If you are using a spherical cutter for the machining operation, you can
optimize the surface finish in the following way:
When milling twisted surfaces, program the main cutting direction
(from point 1 to point 2) perpendicular to the direction of the
steepest inclination.
Please note while programming:
From the current position, the TNC positions the tool in a
linear 3-D movement to the starting point 1. Pre-position
the tool in such a way that no collision between tool and
fixtures can occur.
The TNC moves the tool with radius compensation R0 to
the programmed positions.
If required, use a center-cut end mill (ISO 1641).
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1 to point 2 and in the total
3 / 4. You can program point
1 greater than
1 smaller than
1 at
Fixed Cycles: Multipass Milling