FANUC Series 16/18/160/180-Model C for Lathe Operator Manual

APPENDIX
D. NOMOGRAPHS
B–62754EN/01
744
The leads of a thread are generally incorrect in δ
1
and δ
2
, as shown in Fig.
D.1 (a)
, due to automatic acceleration and deceleration.
Thus distance allowances must be made to the extent of δ
1
and δ
2
in the
program.
Fig.D.1(a) Incorrect thread position
δ
2
δ
1
2
+ T
1
V
V +
1
60
RL
T
1
: Time constant of servo system (sec)
V : Cutting speed (mm/sec)
R : Spindle speed (rpm)
L : Thread feed (mm)
Time constant T
1
(sec) of
the servo system: Usually
0.033 s.
(1). . . . . . .
(mm)
1
+ {t–T
1
) T
1
exp(
t
T
1
)}V
a + exp(
t
T
1
)
(2). . . . . . .
(3). . . . . . .
T
1
: Time constant of servo system (sec)
V : Cutting speed (mm/sec)
Time constant T
1
(sec) of
the servo system: Usually
0.033 s.
The lead at the beginning of thread cutting is shorter than the specified
lead L, and the allowable lead error is L. Then as follows.
a +
L
L
When the value of HαI is determined, the time lapse until the thread
accuracy is attained. The time HtI is substituted in (2) to determine δ
1
:
Constants V and T
1
are determined in the same way as for δ
2
. Since the
calculation of δ
1
is rather complex, a nomography is provided on the
following pages.
D.1
INCORRECT
THREADED LENGTH
Explanations
D How to determine δ
2
D How to determine δ
1

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