Siemens SINUMERIK 808D ADVANCED Programming And Operating Manual page 163

See the following illustration for the example of infeed depth:
Machining section 1 has a total depth of 39 mm. If the maximum infeed depth is 5 mm, eight roughing cuts are required.
These are carried out with an infeed of 4.875 mm.
In machining step 2, 8 roughing steps, too, are carried out with an infeed of 4.5 mm each (total difference 36 mm).
In machining step 3, two roughing passes are carried out with a current infeed of 3.5 (total difference 7 mm).
FAL, FALZ and FALX (finishing allowance)
A finishing allowance for roughing can be specified either using the parameters FALZ and FALX if you want to specify
different finishing allowances axis-specifically or via the parameter FAL for a finishing allowance that follows the contour. In
this case, this value is taken into account in both axes as a finishing allowance.
No plausibility check is carried out for the programmed values. In other words: If all three parameters are assigned values,
all these finishing allowances are taken into account by the cycle. It is, however, reasonable to decide either on the one or
other form of definition of a finishing allowance.
Roughing is always carried out up to these finishing allowances. The resulting residual corner is also removed parallel to the
contour after each paraxial roughing process immediately so that no additional residual corner cut is required after
completion of roughing. If no finishing allowances are programmed, stock is removed when roughing up to the final contour.
FF1, FF2 and FF3 (feedrate)
It is possible to specify different feedrates for the individual machining steps, as shown in Figure NO TAG.
Programming and Operating Manual (Turning)
163
6FC5398-5DP10-0BA2, 06/2015