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Design Info
Pulley Guidelines
When cable is used over pulleys, the cable life can be significantly prolonged by proper groove design. Laboratory tests prove that improper groove design reduces cable bending life to 90%. These same tests show that doubling a pulley diameter can increase cable bending life up to thirteen times. Also, pulley diameters less than sixteen rope diameters fall into a range in which cable life is relatively low.
Cable life is reduced as the groove radius changes from the contour of the cable to a flat surface. For maximum cable life, the groove should make contact with the cable on at least 1/3 of the cable circumference.
Recommended Minimum Pulley Diameters to Maximize Life
| Cable Construction |
Pulley Diameters (Root) |
| 3 x 7 |
50 times rope (uncoated dia.) |
| 7 x 7 |
40 times rope (uncoated dia.) |
| 7 x 19 |
25 times rope (uncoated dia.) |
| 7 x 49 |
15 times rope (uncoated dia.) |
How Pulley Size Affects Cable Strength
The radius of bend has affect on the strengh of cable. In order to take this into account in selecting the size pulley to be used with a given diameter cable, the following table can be used as a guide:
| Ratio "A" = Pulley DIA./Cable DIA. |
Strength Efficiency Compared
to Catalog Strength In % |
| 40 |
95 |
| 30 |
93 |
| 20 |
91 |
| 15 |
89 |
| 10 |
86 |
| 8 |
83 |
| 6 |
79 |
| 4 |
75 |
| 2 |
65 |
| 1 |
50 |
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