How to Use a Plumb Bob for Accurate Vertical Alignment

  • Beginner
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What You'll Need
Plumb bob
Tape measure

A plumb bob is a simple old fashioned tool that is used by builders and DIY enthusiasts to measure the exact vertical alignment in structures. It is a tool that has been used since the Ancient Egyptians and uses gravity to pinpoint the exact vertical. You can straighten windows, doors, and any other tall structures using this device. The plumb bob is both accurate and cheap, which makes it a great addition to your tool collection.

Step 1 - Preparation

A plumb bob is a weighted metal or brass bulb that hangs from a length of the string. It comes in all weights and sizes, so you will need to pick the most appropriate for your job. For use in the home, a bob of between 4 and 10 ounces is advisable. If it comes without string, you could try using household cotton string or any string that has no stretch. It could be helpful to have a range of string lengths to hand in case the structures you are measuring vary in length.

If the structure is high enough to need a ladder, make sure your ladder is placed securely on stable ground. Only use a plumb bob outside when there is little wind, as the slightest breeze could alter the alignment and give you incorrect measurements. If working outside, a heavier bob can help prevent any misreading from breezes.

Step 2 - Setting up the Plumb Bob

If there isn't a string already attached to your plumb bob, you need to fasten one to the top of the tool where you can see a hole in the center of the removable head, unless it is equipped with an eyelet instead at the top into which the string can be tied. The other end of the string will need to be secured at the reference point you're measuring from onto a nail has been partly driven-in for that purpose of hanging the plumb bob from.

Step 3 - Hang the Plumb Bob

Partially drive a nail or a screw into the top of the wall or the ceiling about an inch or two from the outside corner of your wall frame. The weight of the bob will force the string into a perfect line; this measurement should be taken as a reference point. Make sure you allow the plumb bob to hang slightly above the floor, leaving just enough room for it to swing freely.

To straighten a doorway, attach the plumb bob above the door frame and leave it to hang. Measure the distance from the string to the sides of the door frame at the top and bottom using a tape measure. The frame should be adjusted until both of these measurements are equal. This will correctly align your doorway.

Step 4 - Transfer Measurements

To get the floor coordinates from your ceiling points, nail the end of the string to the top point, and wait for the bob to stop moving. Where the point of the plumb bob falls is the exact aligned spot, so mark it with a pencil.