How to Use A Plumb Bob. The plumb bob is an old-fashioned tool that is still in wide use today because of its accuracy. A simple brass or metal bulb with a point on the end uses gravity to help builders determine exact vertical alignment. Whenever you need to straighten a doorway, wall or other tall vertical structure that is longer than a conventional level, try a plumb bob. It's easy and inexpensive. Read on to learn how to use a plumb bob.
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Select a plumb bob that has some weight to it. They come in all sizes and weights, but for typical home use, you will need one between 4 and 10 oz. If string doesn't come with it, you can use just about any string that doesn't stretch. Cotton is a good choice.
Align a wall vertically by measuring and cutting a length of string as long as the distance from the floor to the ceiling. Fasten one end of the string by tying to the head of the plumb bob. There will be a loop or hole provided.
Nail the other end (the top end) to the ceiling an inch or two away from the outside corner of your wall frame. The plumb bob, because it is heavy, will form a perfectly vertical line from the ceiling to the floor. Use this as a reference to adjust your wall frame.
Transfer ceiling points to the exact vertical floor coordinate by nailing the string end to the top point and waiting until the plumb bob quits moving. The bottom point will be hanging directly over the aligned spot. Mark it out with a pencil for future reference.
Straighten a doorway by nailing the plumb bob in the wall, just above the center of the frame and allowing it to hang down the middle. Use a tape measure to determine the distance from the string to the frame sides at both the top and the bottom. Adjust the frame until both measurements are equal.
Use the plumb bob outside only when the wind is not blowing. Even a slight breeze will cause it to move, throwing off the alignment. Choose a heavier plumb bob for outside use even in windless conditions to help alleviate this factor.