
9.SPINDLE FUNCTION B-63783EN-1/01
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9.8 RIGID TAPPING
General
In tapping, the feed amount along the Z-axis per spindle rotation must
equal the thread pitch of the tapper. Therefore, the most desirable
tapping satisfies the following equation:
P = F/S
where, P: Thread pitch of the tapper (mm, inch)
F: Z-axis feedrate (mm/min, inch/min)
S: Spindle speed (min
-1
)
In the tapping cycle (G84) and reverse tapping cycle (G74), spindle
rotation and Z-axis feed are controlled independently. This means that
the above equation is not always satisfied. At the bottom of a hole, in
particular, spindle rotation and Z-axis feed both decelerate and stop,
then start moving and accelerate in the opposite direction. Since
spindle rotation and Z-axis feed accelerate/decelerate independently, it
is generally difficult to satisfy the above equation. For accurate tapping,
a spring is generally installed inside the holder of the tapper to provide
compensation.
With the rigid tapping cycle (G84.2) and reverse rigid tapping cycle
(G84.3), spindle rotation and Z-axis feed are controlled so that they are
always synchronized. In normal operation, the spindle rotation is
controlled to achieve the desired speed. In rigid tapping, on the other
hand, the spindle rotation is controlled considering the position also.
Spindle rotation and Z-axis feed are therefore controlled based on
two-axis linear interpolation. As a result, the equation P = F/S can also
be satisfied during deceleration and acceleration near the bottom of the
hole, thus enabling accurate tapping.
Use G84.2 for specifying the rigid tapping cycle, and G84.3 for the
reverse rigid tapping cycle.
The explanation given in this section assumes the tapping axis to be the
Z-axis. In actual operation, whether the tapping axis is always set to the
Z-axis or set to a programmed axis can be specified with bit 0 (FXY) of
parameter No. 6200.