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How to Make a Retractable Pulley

When building a pulley, the first thing to consider is the weight to be lifted or pulled. Lighter weights call for smaller pulleys and cheaper materials; conversely, heavier weights call for larger pulleys and tougher materials. Retractable pulleys are anchored to a base by a rope that passes around the wheel, and the wheel moves as the pulley is used, as opposed to a pulley whose wheel is stationary. Since retractable pulleys require a strong base, you must take into account the strength of the base itself.

Instructions

- 1
  Take the weight of the objects to be pulled or lifted and multiply that weight by 4. The tensile strength of the rope used must equal this number, as the working load for rope is roughly 25 percent of the total tensile strength. Note that since your retractable pulley must be tethered to a base, there must be a knot somewhere in the rope, which reduces the tensile strength by 50 percent at the point where the knot is tied.
- 2
  Find the thickness of the rope, and use this in combination with the weight of the objects lifted to select the correct pulley wheel. Pulley wheels usually accommodate one size of rope and have a maximum weight specified by the manufacturer. The pulley wheel should be a bare pulley wheel with a spoke and no extra accouterments.
- 3
  Anchor one end of the rope to your intended base. For example, if you are making a clothesline pulley, you should anchor the rope to one of the poles holding up the clothesline; you can do this by tying the rope to the base. Use another length of rope, having the same gauge as the original rope, to attach the spokes of the pulley either to the item to be lifted, or to a container which can hold the items.
- 4
  Feed one end of the anchored rope around the rim of the pulley, and pull it until it is taut. The pulley should be held up and suspended by the rope tension between the load and the and the base. Tie the other end of the anchored rope to the base with a loose knot. To use your pulley, untie one end and pull the rope until you have moved the load the desired distance.

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