9
PM-236 v4 -207.indd
Figure 3-2
Using the threading dial
The dial worm gear has 16T; the leadscrew is 8 TPI,
so the carriage moves 2 inches for each revolution of
the dial when the split-nut is disengaged (when the
split-nut is engaged the dial is stationary).
The symbol "/" in the table means "forget the dial"
— engage at random for any TPI value that is an
even multiple of 4. For
all other
standard TPI threads
the split-nut is engaged when the datum coincides
with a specific line — or lines — on the threading dial.
1 - 8
Not the same as "/" (re-engage anywhere). Ap-
plies to TPI values that are odd multiples of 4; start on
any line (not a half space), re-engage on any line.
2.4.6.8
Applies to even number TPI values that are not multiples of 4 (10, 14, etc.): re-engage at the line you started with
OR
any other line at right angles to it — start on 1, re-engage on 3, 5 or 7; or, start on 2, re-engage on 4, 6 or 8.
4.8
Applies to odd number TPI values (7, etc.): re-engage at the line you started with
OR
the diametrically opposite line — can
be any line pair, 1 & 5, 2 & 6, etc., not necessarily 4 & 8.
8
Applies to fractional values (4-1/2, etc.): re-engage on the
same line
you started with for the first pass — can be any line
number, not just the 8.
TPI
Line
TPI
Line
TPI
Line
TPI
Line
4
/
8
/
16
/
32
/
4-1/2
8
9
4.8
18
2.4.6.8
36
1 - 8
9-1/2
8
19
8
38
2.4.6.8
5
4.8
10
2.4.6.8
20
1 - 8
40
/
5-1/2
8
11
4.8
22
2.4.6.8
44
1 - 8
6
4.8
12
1 - 8
24
/
48
/
6-1/2
8
13
4.8
26
2.4.6.8
52
1 - 8
7
4.8
14
2.4.6.8
28
1 - 8
56
/
7-1/2
8
15
4.8
30
2.4.6.8
THREADS PER INCH
UPPER
GEAR 24T
Speed
MII
16
18
19
20
22
24
26
28
30
MI
32
36
38
40
44
48
52
56
60
Gearbox
A2
A3
C3
A4
C3
C3
C3
A5
B4
Lower gear
48T
, exceptions in
RED
38
44
52
THREADS PER INCH
UPPER
GEAR 48T
Speed
MII
4
4-1/2 9-1/2
5
5-1/2
6
6-1/2
7
7-1/2
MI
8
9
19
10
11
12
13
14
15
Gearbox
A2
A3
C3
A4
C3
C3
C3
A5
B4
Lower gear
24T
, exceptions in
RED
38
22
26
Figure 3-20
Gear-
box and external
gear selections
for standard
threads
Figure 3-22
Threading dial
visualization for
selected U.S.
threads