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Loos & Company Technical Information

Loos & Company Glossary of Terms

Technical Information

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Pulley Diameter

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Standard Length Tolerances

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Cable Diameter Related to Pulley or Sheave Diameter

The service life of Cable and Wire Rope can be increased if (1) it operates over the largest possible pulley or sheave diameter, and (2) it is properly supported in the pulley or sheave groove. The Working life of the individual wire strands is greatly reduced as the pulley or sheave diameter is diminished. The chart  below shows minimum tread diameters
over which various sizes and constructions of cable should operate.


Minimum Tread Diameter for Pulleys or Sheaves

Ratio of cable diameter to pulley diameter

Desirable Minimum

Critical Minimum

42:1 24:1 12:1 28:1 18:1 10:1

Cable Diameter

in Inches

6x7

or

7x7

6x19

or

7x19

6x31

7x31

6x37

6x7

or

7x7

6x19

or

7x19

6x31

7x31

6x37

1/16 2-5/8 ---- ---- 1-3/4 ---- ----
3/32 2-15/16 2-1/4 ---- 2-5/8 1-11/16 ----
1/8 5-1/4 3 ---- 3-1/2 2-1/4 ----
5/32 6-9/16 3-3/4 ---- 4-3/8 2-7/8 ----
3/16 7-7/8 4-1/2 ---- 5-1/4 3-3/8 ----
7/32 9-13/16 5-1/4 ---- 6-1/8 4 ----
1/4 10-1/2 6 3 7 4-1/2 2-1/2
5/16 13-1/8 7-1/2 3-3/4 8-3/4 5-5/8 3-1/8
3/8 15-3/4 9 4-1/2 10-1/2 6-3/4 3-3/4
7/16 18-3/8 10-1/2 5-1/4 12-1/4 7-7/8 4-3/8
1/2 21 12 6 14 9 5

**When designing Aircraft Control Cable Systems, minimum ratio of cable diameter to pulley diameter is 35:1

Pulley Grooves

When designing a pulley groove, the groove should be 150% the maximum tolerance of the wire rope.

Example:

A 1/8" 7x19 aircraft cable has a minimum tolerance of .014" (.125" minimum, .139" maximum). Multiplying the .014" maximum tolerance by 150% = .021". Adding .021" to the .139" maximum diameter = .160", which should be the pulley groove dimension.