Machinery's Handbook, 31st Edition
1832
Set Screws
1 ∕ 2 -inch (12.7 mm) diameter set screws the safe holding force is 500 pounds (2224 N), for 3 ∕ 4 -inch (19 mm) diameter set screws the safe holding force is 1300 pounds (5783 N), and for 1-inch (25.4 mm) diameter set screws the safe holding force is 2500 pounds (11121 N). The power or torque that can be safely transmitted by a set screw may be determined from the formulas, P = ( DNd 2.3 ) ÷ 50; or T = 1250 Dd 2.3 in which P is the horsepower trans mitted; T is the torque in inch-pounds transmitted; D is the shaft diameter in inches; N is the speed of the shaft in revolutions per minute; and d is the diameter of the set screw in inches. Example: How many 1 ∕ 2 -inch diameter set screws would be required to transmit 3 horse power at a shaft speed of 1000 rpm if the shaft diameter is 1 inch? Using the first formula given above, the power transmitted by a single 1 ∕ 2 -inch diameter set screw is determined: P = [1 × 1000 × ( 1 ∕ 2 ) 2.3 ] ÷ 50 = 4.1 hp. Therefore a single 1 ∕ 2 -inch diameter set screw is sufficient. Example: In the previous example, how many 3 ∕ 8 -inch diameter set screws would be required? P = [1 × 1000 × ( 3 ∕ 8 ) 2.3 ] ÷ 50 = 2.1 hp. Therefore two 3 ∕ 8 -inch diameter set screws are required. Table 5. British Standard Whitworth (BSW) and British Standard Fine (BSF) Bright Square Head Set Screws (With Flat Chamfered Ends)
C
E
A
B
F
D
H
H
H
K
K
K
45°
45°
G
45°
G
G
No. 1 Standard
No. 2 Standard
No. 3 Standard
Nominal Size and Max. Dia., Inches
Number of Threads per Inch
Width Across Flats A
Depth of Head B 0.250 0.313 0.375 0.438 0.500 0.625 0.750 0.875 1.000
Width Across Flats C
Depth of Head D 0.250 0.313 0.375 0.438 0.500 0.625 0.750 0.875 1.000
Width Across Flats E
Depth of Head F 0.250 0.313 0.375 0.438 0.500 0.625 0.750 0.875 1.000
BSW
BSF
20 18 16 14 12 11 10
26 22 20 18 16 14 12 11 10
0.250 0.313 0.375 0.438 0.500 0.625 0.750 0.875 1.000
0.313 0.375 0.438 0.500 0.563 0.750 0.875 1.000 1.125
0.375 0.438 0.500 0.625 0.750 0.875 1.000 1.125 1.250
1 ∕ 4
5 ∕ 16
3 ∕ 8
7 ∕ 16
1 ∕ 2
5 ∕ 8
3 ∕ 4
9 8
7 ∕ 8
1
* Depth of Head B , D and F same as for Width Across Flats, No. 1 Standard. Dimensions A , B , C , D , E , and F are in inches.
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