How to Use a Drum Micrometer

How to Use a Drum Micrometer

How to Use a Drum Micrometer : Multi-thousand tips to make your life easier.

Do you need to find out the exact measurement of your brake drum’s inside diameter? Then learn how to properly use a drum micrometer.  Once you become more familiar with the tool, you can readily work on your car’s drum brake systems, especially if you have a four-wheel antique. You can use it to take care of your car’s rear brakes, too.

Understand that your brake drum’s inside diameter begins to wear during the brake shoe replacement process. Watch out for your brake drum when you machine it on a lathe. After a while, your brake drum’s inside diameter changes. When the drum becomes too thin or its inside diameter becomes too wide, it will become less effective.

Don’t forget that all vehicle types have a so-called “discard” measurement for brake drums. The “discard” measurement sets the limit on how far your brake drum’s inside diameter can go. A drum micrometer can help you determine how close your brake drum is to the “discard” measurement.

Here are some guidelines for you:

• Lay your brake drum upside down on a working table. Make sure the surface is level. You should also check your brake drum’s inside diameter. Is it facing upward? If not, adjust it accordingly.
• Inspect your brake drum’s inside diameter. Do you notice any heat cracks? Is scoring already present? Scoring leads to uneven surfaces. Uneven surfaces can cut deeply into your brake drum’s interior surface. Why?  It is where you place your brake shoes.
• If scoring is already present, examine it further. Which score line is the deepest?  Bring out your drum micrometer to measure it. That should let you know if you can machine your brake drum.
• Check the indicators on your drum micrometer. Are they properly positioned? Are they evenly distributed inside your brake drum? If not, exert pressure on them. Keep the pressure light and even. The pressure will let the misplaced indicators fit or line up with the scoring in your brake drum’s inside diameter.
• Hold your brake drum. You can ask someone to help you, if necessary. Otherwise, simply position your hands at each end of your drum micrometer. Continue by turning your drum micrometer.
• Move the drum micrometer clockwise around your brake drum’s inside circumference. Focus on your drum micrometer’s dial indicator. Is there any variance? Measure it. A measurement anomaly clearly indicates that your brake drum has started warping. In other words, it is already useless.
• Record the exact measurement indicated in your drum micrometer’s reading. Compare your reading with the circumference measurement. Is there any variance? 
• Generally, you can find a measurement stamp on your brake drum. It is right on the outside face. The measurement stamp reads: “machine to.” This should be your last consideration. Once you have checked its measurement, you can tell if your brake drum has to be replaced. Realize that reading the measurement may be challenging because the part has been exposed. 

The entire process may turn out to be tedious.  So be patient. You may have to remove any dust or rust, if needed.