Machinery's Handbook, 31st Edition
MEASURING SCREW THREADS 2131 Table for Measuring Whitworth Standard Threads by the Three-wire Method Dia. of Thread No. of Threads per Inch Dia. of Wire Used Dia. Measured over Wires Dia. of Thread No. of Threads per Inch Dia. of Wire Used Dia. Measured over Wires 1 ∕ 8 40 0.018 0.1420 2 1 ∕ 4 4 0.150 2.3247 3 ∕ 16 24 0.030 0.2158 2 3 ∕ 8 4 0.150 2.4497 1 ∕ 4 20 0.035 0.2808 2 1 ∕ 2 4 0.150 2.5747 5 ∕ 16 18 0.040 0.3502 2 5 ∕ 8 4 0.150 2.6997 3 ∕ 8 16 0.040 0.4015 2 3 ∕ 4 3 1 ∕ 2 0.200 2.9257 7 ∕ 16 14 0.050 0.4815 2 7 ∕ 8 3 1 ∕ 2 0.200 3.0507 1 ∕ 2 12 0.050 0.5249 3 3 1 ∕ 2 0.200 3.1757 9 ∕ 16 12 0.050 0.5874 3 1 ∕ 8 3 1 ∕ 2 0.200 3.3007 5 ∕ 8 11 0.070 0.7011 3 1 ∕ 4 3 1 ∕ 4 0.200 3.3905 11 ∕ 16 11 0.070 0.7636 3 3 ∕ 8 3 1 ∕ 4 0.200 3.5155 3 ∕ 4 10 0.070 0.8115 3 1 ∕ 2 3 1 ∕ 4 0.200 3.6405 13 ∕ 16 10 0.070 0.8740 3 5 ∕ 8 3 1 ∕ 4 0.200 3.7655 7 ∕ 8 9 0.070 0.9187 3 3 ∕ 4 3 0.200 3.8495 15 ∕ 16 9 0.070 0.9812 3 7 ∕ 8 3 0.200 3.9745 1 8 0.090 1.0848 4 3 0.200 4.0995 1 1 ∕ 16 8 0.090 1.1473 4 1 ∕ 8 3 0.200 4.2245 1 1 ∕ 8 7 0.090 1.1812 4 1 ∕ 4 2 7 ∕ 8 0.250 4.4846 1 3 ∕ 16 7 0.090 1.2437 4 3 ∕ 8 2 7 ∕ 8 0.250 4.6096 1 1 ∕ 4 7 0.090 1.3062 4 1 ∕ 2 2 7 ∕ 8 0.250 4.7346 1 5 ∕ 16 7 0.090 1.3687 4 5 ∕ 8 2 7 ∕ 8 0.250 4.8596 1 3 ∕ 8 6 0.120 1.4881 4 3 ∕ 4 2 3 ∕ 4 0.250 4.9593 1 7 ∕ 16 6 0.120 1.5506 4 7 ∕ 8 2 3 ∕ 4 0.250 5.0843 1 1 ∕ 2 6 0.120 1.6131 5 2 3 ∕ 4 0.250 5.2093 1 9 ∕ 16 6 0.120 1.6756 5 1 ∕ 8 2 3 ∕ 4 0.250 5.3343 1 5 ∕ 8 5 0.120 1.6847 5 1 ∕ 4 2 5 ∕ 8 0.250 5.4316 1 11 ∕ 16 5 0.120 1.7472 5 3 ∕ 8 2 5 ∕ 8 0.250 5.5566 1 3 ∕ 4 5 0.120 1.8097 5 1 ∕ 2 2 5 ∕ 8 0.250 5.6816 1 13 ∕ 16 5 0.120 1.8722 5 5 ∕ 8 2 5 ∕ 8 0.250 5.8066 1 7 ∕ 8 4 1 ∕ 2 0.150 1.9942 5 3 ∕ 4 2 1 ∕ 2 0.250 5.9011 1 15 ∕ 16 4 1 ∕ 2 0.150 2.0567 5 7 ∕ 8 2 1 ∕ 2 0.250 6.0261 2 4 1 ∕ 2 0.150 2.1192 6 2 1 ∕ 2 0.250 6.1511 2 1 ∕ 8 4 1 ∕ 2 0.150 2.2442 … … … … All dimensions are given in inches. Case 1: The screw thread or worm is to be milled with a cutter having an included angle equal to the nominal or standard thread angle that is assumed to be the angle in the axial plane. For example, a 60-degree cutter is to be used for milling a thread. In this case, the thread angle in the plane of the axis will exceed 60 degrees by an amount increasing with the lead angle. This variation from the standard angle may be of little or no practical importance if the lead angle is small or if the mating nut (or teeth in worm gearing) is formed to suit the thread as milled. Case 2: The screw thread or worm is to be milled with a cutter reduced to whatever normal angle is equivalent to the standard thread angle in the axial plane. For example, a 29-degree Acme thread is to be milled with a cutter having some angle smaller than 29 degrees (the reduction increasing with the lead angle) to make the thread angle standard in the plane of the axis. Theoretically, the milling cutter angle should always be corrected to suit the normal angle; but if the lead angle is small, such correction may be unnecessary.
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