14. FUNCTIONS TO SIMPLIFY
A drilling G code specifies positioning axes and a drilling axis as shown
below. The C–axis and X– or Z–axis are used as positioning axes. The
X– or Z–axis, which is not used as a positioning axis, is used as a drilling
Although canned cycles include tapping and boring cycles as well as
drilling cycles, in this chapter, only the term drilling will be used to refer
to operations implemented with canned cycles.
Table14.1(b) Positioning axis and drilling axis
Positioning plane Drilling axis
G83, G84, G85 X axis, C axis Z axis
G87, G88, G89 Z axis, C axis X axis
G83 and G87, G84 and G88, and G85 and G89 have the same function
respectively except for axes specified as positioning axes and a drilling
G83AG85 / G87A89 are modal G codes and remain in effect until
canceled. When in effect, the current state is the drilling mode.
Once drilling data is specified in the drilling mode, the data is retained
until modified or canceled.
Specify all necessary drilling data at the beginning of canned cycles; when
canned cycles are being performed, specify data modifications only.
In G code system A, the tool returns to the initial level from the bottom
of a hole. In G code system B or C, specifying G98 returns the tool to the
initial level from the bottom of a hole and specifying G99 returns the tool
to the point–R level from the bottom of a hole.
The following illustrates how the tool moves when G98 or G99 is
specified. Generally, G99 is used for the first drilling operation and G98
is used for the last drilling operation.
The initial level does not change even when drilling is performed in the
G98(Return to initial level ) G99(Return to point R level)
Point R level
D Drilling mode
D Return point level