Synchronous Drive Specifications

SCOPE

This standard applies to those belts and pulleys intended for mechanical power transmission, and where positive indexing or synchronous type service may be required. These specifications cover three standard belt sections, which are established on the basis of belt pitch. These sections are designated MXL (0.080 inch pitch), XL (0.200 inch pitch), and L (0.375 inch pitch). It also covers dimensions for two double-sided sections: DXL (0.200 inch pitch), and DL (0.375 inch pitch). Dimensions of synchronous belts and pulleys together with basic design data are covered in this standard. Dimensions in customary English units are provided. This standard does not apply to automotive drives for which other standards exist.

SYNCHRONOUS BELT PULLEYS

DIAMETERS

Table 1 lists the standard pulley diameters by belt section (pitch). Figure 1 defines the pitch, pitch diameter, outside diameter, and the pitch line differential.

WIDTHS

The standard pulley widths are shown in Table 2 for each belt section. The nominal pulley width is specified in terms of the maximum standard belt width the pulley will accommodate. For example, only one standard nominal width is specified for the XL Belt Section – 0.38 inches. This pulley width can be used for the standard XL belt widths of 0.25 and 0.38 inches. The actual minimum pulley width, whether flanged or unflanged, is also specified in Table 2 and shown in Figures 2 and 3.

SIZE DESIGNATION

Pulleys are designated by the number of grooves, the belt section, and a number representing 100 times the nominal width. For example, a 30 groove L section pulley with a nominal width of 0.75 inches would be designated by the number 30L075.

GROOVE PROFILE

The groove profile is defined as the profile formed by the generating tool rack form described in Table 3 and Figure 4. The sides of the grooves shall be free of surface defects, and the edges of all grooves shall be rounded. The flanks of the grooves shall have a finish of 125 microinches, or better.

FLANGE DIMENSIONS

The details of suggested pulley flange design are shown in Table 4 and Figure 5.

KEYSEATS

Keyseats in the hubs of pulleys are shown in Figure 6 and shall conform to the dimensions and tolerances given in Table 5. BORE

TOLERANCES

Table 6 gives the bore tolerances for belt pulleys.

MISCELLANEOUS TOLERANCES

Table 7 includes the following miscellaneous pulley tolerances: Outside Diameter, Radial Runout, Axial Runout, Pitch Accuracy

Table 1  Standard Pulley Diameters – Inches
No. of
Grooves		 BELT SELECTION
MXL (0.080)
Diameters		 XL (0.200)
Diameters		 L (0.375)
Diameters
Pitch Outside Pitch Outside Pitch Outside
10 0.255 0.235 0.637 0.617 1.194* 1.164*
12 0.306 0.286 0.764 0.744 1.432* 1.402*
14 0.357 0.337 0.891 0.871 1.671 1.641
16 0.407 0.387 1.019 0.999 1.910 1.880
18 0.458 0.438 1.146 1.126 2.149 2.119
20 0.509 0.489 1.273 1.253 2.387 2.357
22 0.560 0.540 1.401 1.381 2.626 2.596
24 0.611 0.591 1.528 1.508 2.865 2.835
26 0.662 0.642 3.104 3.074
28 0.713 0.693 1.783 1.763 3.342 3.312
30 0.764 0.744 1.910 1.890 3.581 3.551
32 0.815 0.795 2.037 2.017 3.820 3.790
34 0.866 0.846
36 0.917 0.897 2.292 2.272 4.297 4.267
40 1.019 0.999 2.546 2.526 4.775 4.745
42 1.070 1.050 2.674 2.654
44 1.120 1.100 2.801 2.781 5.252 5.222
48 1.222 1.202 3.056 3.036 5.730 5.700
60 1.528 1.508 3.820 3.800 7.162 7.132
72 1.833 1.813 4.584 4.564 8.594 8.564
84 10.027 9.997

* Usually not available in all widths - consult supplier

Figure 1 Pulley Dimensions

Table 2 Standard Pulley Widths – Inches (See Figures 2 & 3)
BELT SELECTION STANDARD NOMINAL PULLEY WIDTH STANDARD PULLEY WIDTH DESIGNATION MINIMUM PULLEY WIDTH
FLANGED
bf		 UNFLANGED
bf
MXL (0.080) 0.25 025 0.28 0.35
XL (0.200) 0.38 037 0.41 0.48
L (0.375) 0.50 050 0.55 0.67
0.75 075 0.80 0.92
1.00 100 1.05 1.17
Table 3 Pulley Generating Tool Rack Form Dimensions – Inches (See Figures 1 & 4)
BELT SELECTION NUMBER OF
GROOVES		 Pb
± 0.0001		 β
± 0.25
(Degrees)		 hr
+0.002
-0.000		 bg
+0.002
-0.000		 r1
± 0.001		 r2
± 0.001		 2a
MXL 10 thru 23
24 & over		 0.0800 56
40		 0.025 0.024
0.265		 0.012 0.009 0.020
XL 10 & over 0.2000 50 0.055 0.050 0.024 0.024 0.020
L 10 & over 0.3750 40 0.084 0.122 0.034 0.021 0.030

Pulley generating tool rack form

Table 4 Flange Dimensions – Inches (See Figure 5)
BELT SELECTION MINIMUM FLANGE THICKNESS MINIMUM FLANGE HEIGHT*
*Flange outside diameter equals pulley outside diameter plus twice flange height.
MXL (0.080) 0.023 0.020
XL (0.200) 0.029 0.040
L (0.375) 0.050 0.065

Table 5 Standard Hub Keyseat Dimensions – Inches (See Figure 6)
SHAFT DIAMETER WIDTH, wk* DEPTH, wk*
+0.015
-0.000
*Tolerance on width, wk:
For width up through 1/2 (0.500)......+0.002, -0.000 inches
For width over 1/2 (0.500)
up through 1 (1.000)..........+0.003, -0.000 inches
For width over 1 (1.000).................+0.004, -0.000 inches
Up Through 7/16 (0.44)
Over 7/16 (0.44) To and Incl 9/16 (0.56)
Over 9/16 (0.56) To and Incl 7/8 (0.88)
Over 7/8 (0.88) To and Incl 1-1/4 (1.25)		 3/32 (0.094)
1/8 (0.125)
3/16 (0.188)
1/4 (0.250)		 3/64 (0.047)
1/16 (0.062)
3/32 (0.094)
1/8 (0.125)
Over 1-1/4 (1.25) To and Incl 1-3/8 (1.38)
Over 1-3/8 (1.38) To and Incl 1-3/4 (1.75)
Over 1-3/4 (1.75) To and Incl 2-1/4 (2.25)
Over 2-1/4 (2.25) To and Incl 2-3/4 (2.75)		 5/16 (0.312)
3/8 (0.375)
1/2 (0.500)
5/8 (0.625)		 5/32 (0.156)
3/16 (0.188)
1/4 (0.250)
5/16 (0.312)
Over 2-3/4 (2.75) To and Incl 3-1/4 (3.25)
Over 3-1/4 (3.25) To and Incl 3-3/4 (3.75)
Over 3-3/4 (3.75) To and Incl 4-1/2 (4.50)
Over 4-1/2 (4.50) To and Incl 5-1/2 (5.50)		 3/4 (0.750)
7/8 (0.875)
1 (1.000)
1-1/4 (1.250)		 3/8 (0.375)
7/16 (0.438)
1/2 (0.500)
5/8 (0.625)
Table 6 Pulley Bore Tolerances – Inches
DIAMETER OF BORE LENGTH OF BORE
Up Thru 0.75 Over 0.75 To And Including 1.00 Over 1.00 To And Including 1.25 Over 1.25 To And Including 1.50 Over 1.50 To And Including 2.00 Over 2.00 To And Including 2.50 Over 2.50 To And Including 3.00 Over 3.00 To And Including 3.50 Over 3.50 To And Including 4.00 Over 4.00 To And Including 4.50 Over 4.50 To And Including 5.50 Over 5.50 To And Including 6.00
Up thru 0.50 +0.0015
+0.0005		 +0.0015
+0.0005		 +0.0015
+0.0005		 +0.0015
+0.0005		 +0.0015
+0.0005
Over 0.50 To And Including 1.00 +0.0015
+0.0005		 +0.0015
+0.0005		 +0.0015
+0.0005		 +0.0015
+0.0005		 +0.0020
+0.0005		 +0.0020
+0.0005		 +0.0020
+0.0005
Over 1.00 To And Including 1.50 +0.0015
+0.0005		 +0.0015
+0.0005		 +0.0015
+0.0005		 +0.0020
+0.0010		 +0.0020
+0.0010		 +0.0020
+0.0010		 +0.0020
+0.0010		 +0.0000
+0.0010
Over 1.50 To And Including 2.00 +0.0020
+0.0005		 +0.0020
+0.0005		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0030
+0.0010
Over 2.00 To And Including 2.50 +0.0020
+0.0005		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0030
+0.0010
Over 2.50 To And Including 3.00 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0025
+0.0010		 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0035
+0.0015
Over 3.00 To And Including 3.50 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0035
+0.0010		 +0.0035
+0.0010		 +0.0040
+0.0015
Over 3.50 To And Including 4.00 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0040
+0.0015		 +0.0040
+0.0015		 +0.0040
+0.0015
Over 4.00 To And Including 4.50 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0040
+0.0015		 +0.0040
+0.0015		 +0.0040
+0.0015
Over 4.50 To And Including 5.00 +0.0030
+0.0010		 +0.0030
+0.0010		 +0.0040
+0.0015		 +0.0040
+0.0015		 +0.0040
+0.0015

Table 7 Miscellaneous Pulley Tolerances – Inches (All Sections)
OUTSIDE DIAMETER RANGE OUTSIDE DIAMETER TOLERANCE PITCH TO PITCH TOLERANCE
ADJACENT GROOVES ACCUMULATIVE OVER 90 DEGREES
Up Thru 1.000 +0.002
-0.000		 ±0.001 ±0.003
Over 1.000 To And Including 2.000 +0.003
-0.000		 ±0.001 ±0.004
Over 2.000 To And Including 4.000 +0.004
-0.000		 ±0.001 ±0.005
Over 4.000 To And Including 7.000 +0.005
-0.000		 ±0.001 ±0.005
Over 7.000 To And Including 12.000 +0.006
-0.000		 ±0.001 ±0.006
Over 12.000 To And Including 20.000 +0.007
-0.000		 ±0.001 ±0.007
Over 20.000 +0.008
-0.000		 ±0.001 ±0.008

Other Pulley Tolerances

RADIAL RUNOUT*

For outside diameters 8.0 inches
and under .....0.005 inches

For each additional inch of outside diameter
add.....0.0005 inches

AXIAL RUNOUȚ*

For outside diameters 1.0 inches
and under........0.001 inches

For each additional inch of outside diameter
up through 10.0 inches, add......0.001 inches

For each additional inch of outside diameter
over 10.0 inches, add.....0.0005 inches

*Total Indicator Reading