By Dean McDonald, founder, Crane Rope Solutions
A wire rope has a nominal diameter, the size you buy (26 mm or 1-1/4 in), and a diameter tolerance, how much the actual size can vary along its length. A 26 mm rope with a tolerance of 0 to +5% can measure anywhere from 26 mm to 27.3 mm, depending on where you measure it.
Now picture a drum 25 wraps wide. If every wrap is 1.3 mm larger than it should be, the layer is 32.5 mm too wide by the time it reaches the far flange, and the next layer won't spool properly.
That's an extreme case to show the idea, but the problem is real and common. When bad spooling happens, the usual reaction is "we lost tension on the drum," so the crew applies as much tension as they can. Now the rope is shearing against the wrap beside it, and premature wear starts.
From our inspections
Case study: Measuring drum pitch and choosing rope tolerance
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