Page 437 - Shigley's Mechanical Engineering Design
P. 437
bud29281_ch08_409-474.qxd 12/16/2009 7:11 pm Page 412 pinnacle 203:MHDQ196:bud29281:0073529281:bud29281_pagefiles:
412 Mechanical Engineering Design
Table 8–1
Nominal Coarse-Pitch Series Fine-Pitch Series
Diameters and Areas of Major Tensile- Minor- Tensile- Minor-
Stress
Stress
Coarse-Pitch and Fine- Diameter Pitch Area A t Diameter Pitch Area A t Diameter
p
d
p
Area A r
Area A r
Pitch Metric Threads.* mm mm mm 2 mm 2 mm mm 2 mm 2
1.6 0.35 1.27 1.07
2 0.40 2.07 1.79
2.5 0.45 3.39 2.98
3 0.5 5.03 4.47
3.5 0.6 6.78 6.00
4 0.7 8.78 7.75
5 0.8 14.2 12.7
6 1 20.1 17.9
8 1.25 36.6 32.8 1 39.2 36.0
10 1.5 58.0 52.3 1.25 61.2 56.3
12 1.75 84.3 76.3 1.25 92.1 86.0
14 2 115 104 1.5 125 116
16 2 157 144 1.5 167 157
20 2.5 245 225 1.5 272 259
24 3 353 324 2 384 365
30 3.5 561 519 2 621 596
36 4 817 759 2 915 884
42 4.5 1120 1050 2 1260 1230
48 5 1470 1380 2 1670 1630
56 5.5 2030 1910 2 2300 2250
64 6 2680 2520 2 3030 2980
72 6 3460 3280 2 3860 3800
80 6 4340 4140 1.5 4850 4800
90 6 5590 5360 2 6100 6020
100 6 6990 6740 2 7560 7470
110 2 9180 9080
*The equations and data used to develop this table have been obtained from ANSI B1.1-1974 and B18.3.1-1978.
The minor diameter was found from the equation d r = d −1.226 869p, and the pitch diameter from d p = d −
0.649 519p. The mean of the pitch diameter and the minor diameter was used to compute the tensile-stress area.
Square and Acme threads, whose profiles are shown in Fig. 8–3a and b, respec-
tively, are used on screws when power is to be transmitted. Table 8–3 lists the pre-
ferred pitches for inch-series Acme threads. However, other pitches can be and often
are used, since the need for a standard for such threads is not great.
Modifications are frequently made to both Acme and square threads. For instance,
the square thread is sometimes modified by cutting the space between the teeth so as
to have an included thread angle of 10 to 15 . This is not difficult, since these threads
◦
are usually cut with a single-point tool anyhow; the modification retains most of the
high efficiency inherent in square threads and makes the cutting simpler. Acme threads