Smithy CNC Mills - Manual (Page 117)

5. Restart the spindle in the direction it was going.
It is unclear how the operator is to manually move the tool because a change to
manual mode resets the program to the top. We will attempt to clarify that step
in this procedure.
1.11 G89 Cycle
The G89 cycle is intended for boring. This cycle uses a P value, where P speci-
fies the number of seconds to dwell.
0. Preliminary motion, as described above.
1. Move the Z-axis only at the current feed rate to the Z position.
2. Dwell for the given number of seconds.
3. Retract the Z-axis at the current feed rate to clear Z. This cycle is like G82
except that the tool is drawn back at feedrate rather than rapid.
1.12 G98 G99
G98 - initial level return in canned cycles
G99 - R value return in canned cycles
These codes are treated together because they behave very much alike.†You
will recall that when Z is above R the preparatory move is from the current loca-
tion to the X, Y values. If G98 is not specified, then the canned cycle will return
to the R value rather than the Z value that was used on the approach.
N01 G0 X1 Y2 Z3
N02 G90 G81 X4 Y5 Z-0.6 R1.8
Adding G98 to the second line above means that the return move will be to the
value of OLD_Z since it is higher that the R value specified.
SmithyCNC Programmer’s Reference Manual: Mill Canned Cycles
SmithyCNC Programmer’s Reference Manual: Mill Canned Cycle 10-14