Machinery's Handbook, 31st Edition
Synchronous Belts 2613 Widths: Standard pulley widths for each belt section are shown in Table 41. The nominal pulley width is specified in terms of the maximum standard belt width the pulley will ac - commodate. The minimum pulley width, whether flanged or unflanged, is also shown in Table 41 , along with flange dimensions and various pulley tolerances. Pulley Size Designation: Synchronous belt pulleys are designated by the number of grooves, the belt section, and a number representing 100 times the nominal width. For ex- ample, a 30 groove L section pulley with a nominal width of 0.75 in. would be designated by 30L075. Pulley tolerances are shown in Table 45. Table 45. Pulley Tolerances (All Sections)
Pitch to Pitch Tolerance
Outside Diameter Tolerance
Outside Diameter Range
Adjacent Grooves
Accumulative Over 90 Degrees
+0.002 − 0.000 +0.003 − 0.000 +0.004 − 0.000 +0.005 − 0.000 +0.006 − 0.000 +0.007 − 0.000 +0.008 − 0.000
± 0.001 ± 0.001 ± 0.001 ± 0.001 ± 0.001 ± 0.001 ± 0.001
± 0.003 ± 0.004 ± 0.005 ± 0.005 ± 0.006 ± 0.007 ± 0.008
Up thru 1.000
Over 1.000 to and including 2.000 Over 2.000 to and including 4.000 Over 4.000 to and including 7.000 Over 7.000 to and including 12.000 Over 12.000 to and including 20.000
Over 20.000
Radial Runout a
Axial Runout a
For outside diameters 8.0 in. and under 0.005 in. For each additional inch of outside diameter add 0.0005 in.
For outside diameters 1.0 in. and under 0.001 in. For each additional inch of outside diameter up through 10.0 in., add 0.001 in. For each additional inch of outside diameter over 10.0 in., add 0.0005 in.
a Total indicator reading. All dimensions in inches.
Cross Section Selection: The chart (Fig. 14) may be used as a guide to the selection of a synchronous belt for any combination of design horsepower and speed of the faster shaft. When the intersection of the design horsepower and speed of the faster shaft falls near a line between two areas on the chart, the possibilities in both areas should be explored. Special circumstances (such as space limitations) may result in selection of a belt cross section different from that indicated in the chart. Belt manufacturers should be contacted for specific data. Torque Ratings: It is customary to use torque load requirements rather than horsepower load when designing drives using the small pitch MXL section belts. These belts operate on small diameters resulting in relatively low belt speeds, so torque is essentially constant for all rpm. The torque rating formulas for MXL sections are: . . . . . . . . . Q d d Q d d Q d d 113 138 10 012 188 230 10 019 263 321 10 025 for belt width in. for belt width in. for belt width in. 3 2 3 2 3 2 = = − − = = = − = − − − 6 6 6 @ @ @ × × × where Q r = the maximum torque rating (lbf-in.) for a belt of specified width having six or more teeth in mesh and a pulley surface speed of 6500 fpm or less. Torque ratings for drives with less than six teeth in mesh must be corrected as shown in Table 46. d = pitch diameter of smaller pulley, inch. r r r
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