
B–63502EN/01
13. FUNCTIONS TO SIMPLIFY
PROGRAMMING
NC FUNCTION
109
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 (M series), G84/G88 (T series). 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.
Rigid tapping can be performed by executing any of the following
commands:
M29 S fffff before tapping command G74/G84 (M series)
or G84/G88 (T series)
M29 S fffff in the same block as tapping command G74/G84
(M series) or G84/G88 (T series)
G74/G84 (M series) or G84/G88 (T series) as rigid tapping G code
(Whether G74/G84 (G84/G88) is used as rigid tapping G code or
ordinary tapping G code can be selected with a parameter.)
13.2
RIGID TAP