12. FUNCTIONS TO SIMPLIFY
PROGRAMMING
B–63172EN/01
NC FUNCTION
74
In tapping, the feed amount of drilling axis for one rotation of spindle
should be equal to the pitch of screw of tapper. Namely, the following
conditions must be satisfied in the best tapping:
P=F/S,
where P : Pitch of screw of tapper (mm)
F : Feed rate of drilling axis (mm/min)
S : Spindle speed (rpm)
The rotation of spindle and feed of Z axis are independently controlled in
the tapping cycle G74/G84. Therefore, the above conditions may not
always be satisfied. Especially at the hole bottom, both the rotation of
spindle and feed of drilling axis reduce the speed and stop. After that, they
move in the inverse direction while increasing the speed. However, the
above conditions may not be satisfied in general since each
acceleration/deceleration is performed independently. Therefore, in
general, the feed is compensated by mounting a spring to the inside of
holder of tapper to improve the accuracy of tap cutting.
The rotation of spindle and feed of drilling axis are controlled so that they
are always synchronous each other in the rigid tapping cycle. Namely, in
other than rigid tapping, control for speed only is performed. In the rigid
tapping however, position control is also performed during the rotation
of spindle, that is, the rotation of spindle and feed of drilling axis are
controlled as linear interpolation of two axes.
This allows the following condition to be satisfied also during
acceleration/deceleration at the hole bottom and a tapping of improved
accuracy to be made.
P = F/S
The pitch of screw tap can be directly specified.
For rigid tapping, specify M29 Sfffff before tapping command
G74/G84.
Rigid tapping can be canceled by G80 (canned cycle cancel).
Distributed
pulse
Spindle
motor
Gear ratio
n : m
Spindle
Gear ratio
1 : p
Spindle
amplifier
D/A
converter
Position
coder
Error
counter
Spindle control
(voltage calculation of
spindle speed rpm)
×4
DMR
×4
CMR
12.2
RIGID TAP (ONLY
FOR Power Mate i–D)