Synchronous Belts

SIZE DESIGNATIONS

Synchronous Belt sizes are identified by a standard number. The first digits specify the belt length to one-tenth inch followed by the belt section (pitch) designation. The digits following the belt section designation represent the nominal belt width times 100. For example, an L section belt 30.000 inches in pitch length and 0.75 inches in width would be specified as a 300L075 Synchronous Belt. The nomenclature for double-sided belts will be the same as for single-sided belts with the addition of the prefix “D” in front of the belt section – Example 300DL075.

STANDARD SECTIONS

Belt sections are specified in terms of “pitch”. Table 8 gives the Standard Belt Sections and their corresponding “pitch”.  

NOMINAL TOOTH DIMENSIONS

Table 9 and Figure 7 show the nominal tooth dimensions for each of the standard belt sections. The tooth dimensions for double-sided belts are identical to those of a single-sided belt.

PITCH LENGTHS

Standard belt pitch lengths, belt length designations and numbers of teeth are shown in Table 10.

WIDTHS

Standard belt widths and width designations are shown in Table 11.

Table 8 Standard Belt Selections - Inches (See Figure 7)
BELT SELECTION PITCH hg hd
MXL 0.080 0.045
XL 0.200 0.090
L 0.375 0.14
DXL 0.200 0.120 0.120
DL 0.375 0.180 0.180
Table 9 Nominal Tooth Dimensions – Inches (See Figure 7)
BELT SELECTION SS TOOTH ANGLE (DEGREES) ht bt ra rr
MXL (0.080) 40 0.020 0.045 0.005 0.005
XL (0.200) 50 0.050 0.101 0.015 0.015
L (0.375) 40 0.075 0.183 0.020 0.020
DXL (0.200) 40 0.050 0.101 0.015 0.015
DL (0.375) 40 0.075 0.183 0.020 0.020
Table 10 Standard Pitch Lengths and Tolerances – Inches (Continued)
BELT LENGTH DESIGNATION PITCH LENGTH PERMISSIBLE DEVIATION FROM STANDARD LENGTH NUMBER OF TEETH FOR STANDARD LENGTHS
MXL (0.080) XL (0.200) L (0.375)
36 3.600 ±0.016 45
40 4.000 ±0.016 50
44 4.400 ±0.016 55
48 4.800 ±0.016 60
56 5.600 ±0.016 70
60 6.000 ±0.016 75 30
64 6.400 ±0.016 80
70 7.000 ±0.016 35
72 7.200 ±0.016 90
80 8.000 ±0.016 100 40
88 8.800 ±0.016 110
90 9.000 ±0.016 45
100 10.000 ±0.016 125 50
110 11.018 ±0.018 55
112 11.200 ±0.018 140
120 12.000 ±0.018 60
124 12.375 ±0.018 33
124 12.400 ±0.018 155
130 13.000 ±0.018 65
140 14.000 ±0.018 175 70
150 15.000 ±0.018 75 40
160 16.000 ±0.020 200 80
170 17.000 ±0.020 85
180 18.000 ±0.020 225 90
187 18.750 ±0.020 50
190 19.000 ±0.020 95
200 20.000 ±0.020 250 100
210 21.000 ±0.024 105 56
220 22.000 ±0.024 110
225 22.500 ±0.024 60
230 23.000 ±0.024 115
240 24.000 ±0.024 120 64
250 25.000 ±0.024 125
255 25.500 ±0.024 68
260 26.000 ±0.024 130
270 27.000 ±0.024 72
285 28.500 ±0.024 76
300 30.000 ±0.024 80
322 32.250 ±0.026 86
330 33.000 ±0.026
Table 10 Standard Pitch Lengths and Tolerances - Inches (Continued 2)
BELT LENGTH DESIGNATION PITCH LENGTH PERMISSIBLE DEVIATION FROM STANDARD LENGTH NUMBER OF TEETH FOR STANDARD LENGTHS
MXL (0.080) XL (0.200) L (0.375)
345 34.500 ±0.026 92
360 36.000 ±0.026
367 36.750 ±0.026 98
390 39.000 ±0.026 104
420 42.000 ±0.030 112
450 45.000 ±0.030 120
480 48.000 ±0.030 128
507 50.750 ±0.032
510 51.000 ±0.032 136
540 54.000 ±0.032 144
560 56.000 ±0.032
570 57.000 ±0.032 160
600 60.000 ±0.032
630 63.000 ±0.034
660 66.000 ±0.034
700 70.000 ±0.034
750 75.000 ±0.036
770 77.000 ±0.036
800 80.000 ±0.036
840 84.000 ±0.038
850 85.000 ±0.038
900 90.000 ±0.038
980 98.000 ±0.040
1000 100.000 ±0.040
1100 110.000 ±0.042
1120 112.000 ±0.044
1200 120.000 ±0.044
1250 125.000 ±0.046
1260 126.000 ±0.046
1400 140.000 ±0.048
1540 154.000 ±0.052
1600 160.000 ±0.052
1700 170.000 ±0.054
1750 175.000 ±0.056
1800 180.000 ±0.056

Figure 7 Tooth Dimensions

Figure 7 Tooth Dimensions

LENGTH TOLERANCES

The belt length tolerances shown in Table 10 apply to all belt sections and represent the total manufacturing tolerance on the belt length. For fixed center drives consult the belt manufacturer.

WIDTH TOLERANCE

Belt width tolerances for all belt sections are given in Table 11.

LENGTH DETERMINATION

The pitch length of a belt shall be determined by placing the belt on a measuring fixture comprising two pulleys of equal diameter, a method of applying force and a means of measuring the center distance between the two pulleys.

One of the two pulleys is fixed in position while the other is movable along a graduated scale. Recommended measuring pulley dimensions are shown in Table 12.

The fixture is shown schematically in Figure 9. Any pair of equal diameter pulleys of the proper pitch and manufactured to the specifications shown in the “Synchronous Belt Pulleys” section may be used for measuring provided the clearance between the theoretical belt tooth width and the groove width of the measuring pulley is not less than the minimum values shown in Table 12. Measuring forces for the standard belt sections and widths are shown in Table 13.

In measuring the length of a belt, the belt should be rotated at least two revolutions of the belt in order to (a) seat the belt properly in the pulley grooves, (b) divide equally the total force between the two strands of the belt, and (c) determine the midpoint of the center distance travel of the movable pulley which shall define the center distance. The pitch length shall be calculated by adding the pitch circumference of one of the measuring pulleys to twice the measured center distance between the two pulleys. 

Table 11 Standard Belt Wtdths and Tolerances — Inches
BELT SELECTION STANDARD BELT WIDTHS TOLERANCES ON WIDTH FOR BELT PITCH LENGTHS
DESIGNATION DIMENSIONS UP TO AND INCLUDING 33 INCHES OVER 33 INCHES UP TO AND INCLUDING 66 INCHES OVER 66 INCHES
MXL (0.080) 012 0.12 +0.02 - -
MXL (0.080) 019 0.19 -0.03
MXL (0.080) 025 0.25
XL (0.200) 025 0.25 +0.02 - -
XL (0.200) -0.03
XL (0.200) 037 0.38
L (0.375) 050 0.50 +0.03 +0.03 -
L (0.375) 075 0.75 -0.03 -0.05
L (0.375) 100 1.00

Measuring pulley and belt and pitch length

Table 12 Belt Length Measuring Pulleys - Inches
* Total Indicator Reading (Maximum)
BELT SELECTION NUMBER OF TEETH PITCH CIRCUMFERENCE OUTSIDE DIAMETER RADIAL RUNOUT T.I.R.* AXIAL RUNOUT T.I.R.* MINIMUM CLEARANCE (SEE FIG. 8)
MXL (0.080) 20 1.600 0.4893
±0.0005		 0.0005 0.001 0.010
XL (0.200) 10 2.000 0.6166
±0.0005		 0.0005 0.001 0.012
L (0.375) 16 6.000 1.8799
±0.0005		 0.0005 0.001 0.013
Table 13 Total Measuring Force — Poundș Force (lbf)
BELT SELECTION BELT WIDTH (INCHES)
0.12 0.19 0.25 0.38 0.50 0.75 1.00 1.50 2.00 3.00 4.00 5.00
MXL (0.080) 3 4.5 5
XL (0.200) 8 12
L (0.375) 24 40 55