What Is a Plumb Bob?
A plumb bob is a pointed metal weight attached to a string used to calibrate a straight vertical line in construction and surveying. Although simple in design, the tool has great accuracy because it relies on the force of gravity to pull the pointed weight plumb, or to a true vertical. The ancient Egyptians used plumb bobs in astronomy, navigation, canal building and the construction of the pyramids. Does this Spark an idea?
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Types of Plumb Bobs
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A plumb bob can be purchased from a hardware store, but you can also fashioned one out of items found at home. A child's spinning top, a conical fishing bobble and a sand-filled tin can with a nail punctured at dead center can all function as a plumb bob weight.
How to Use a Plumb Bob
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Attach the plumb bob to a piece of string. Attach the string to the ceiling or beam perpendicular to the vertical distance to which the plumb bob will align. Allow the plumb bob to dangle down above the parallel floor surface. The plumb bob's weight will pull the string straight, creating a perfectly vertical line to use as a reference.
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A Plumb Bob Versus a Spirit Level
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Many people keep a spirit level, or bubble level, handy to judge the straightness of vertical and horizontal distances in small projects. The advantage of a plumb bob is that its useful range can be extended to much greater distances. A level relies on a straightedge that can balance on the surface of the object that needs adjusting, such as a picture frame. However, a plumb bob can be temporarily attached to a ceiling or hanging beam to establish a true vertical on taller projects, such as repositioning a wall or remodeling a fireplace.
Additional Tips for Operating a Plumb Bob
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To keep a plumb bob from swinging like a pendulum, take a few precautions. Use a plumb bob with a heavy weight of 6 to 8 oz. or more, and use rope that doesn't stretch. Fixing a pulley from the desired vertical height where the plumb bomb should descend can help lower it with less friction, but typically a plumb bob is simply hung from a nail in a wall. Mark the plumb point as soon as the plumb bob stops oscillating. To keep the line plumb for a longer time, suspend the weight in a container of viscous transparent oil.
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