How to Use a Brake Lathe

January 27, 2012

One of the simplest automotive maintenance jobs is the repair of the brake system, and a brake lathe can aid this. While it may seem complex at first, it is only appearance. However, despite the overall simplicity of the task it is still one of precision. Poorly maintained brake pads, rotors and disc can cause the vehicle's brake system to malfunction, or at the least make terrible noise as the owner drives around.

Step 1: Determine the Brake Rotor's Remaining Usefulness.

To utilize a Brake Lathe the first thing that must be determined is the remaining serviceability of the rotor that is about to be smoothed. To determine this you must use a micrometer and acquire the minimum thickness number that is supposed to be cast into the inner part of the rotor. This will vary between manufacturers and is of vital importance. If the rotor is thinner than is allowed then it must be replaced entirely instead of smoothed otherwise this can lead to usage issues and possible brake failure.

Step 2: Mounting

The rotor needs to be mounted on the arbor. This will require the proper adapters and spacers. If you are unaware of what these are then you will have to search online or inquire from the manufacturer. Once the rotor is mounted, place a silencer band around the rotor to keep noise to a minimum. Without this band the project could become intolerably loud.

Step 3: Preparation and Cutting

Rotate the detent knob until it is aligned with the slot in the detent nut. Now move the cutters into place so that the detent pin will align and slide into proper position. Make certain that the cutters are properly aligned on the left and right so that they will fully cut the rotors when in use. The detent nut will require tightening now, but not overly so. Too much torque on the nut can cause the cutters or the nut to become damaged in use.

Now set the speed and control settings to determine a cutting depth of up to 0.030 inches per pass. Most vehicles will not require any form of rough cutting if this or a lesser depth is required.

Once everything is set, turn on the power and watch the spindle turn. Turn the tool bit controls until the tool bits themselves barely make contact with the rotating surface. Turn the dial to zero, and then move the tool bits to toward the inside hub to the location where the rotor face begins.

Determine the cutting depth needed to true the rotor in one pass and set it accordingly. Use the lock knobs to hold the cutters in place and let the machine do its work.

Step 4: Finishing Up

Determine whether the drum boring bar is completely retracted. If it is not, then retract it now. Once it is fully retracted shift the feed selector to "Disc" and the disc feed should automatically start up.

Allow the cutters to reach completely to the edge then set the feed selector to a neutral position and allow the machine to come to a stop. Turn the power off. Recheck everything with the micrometers and determine if further truing will be required. If so, repeat the above steps with the new depths. If it does not require further servicing remove the rotor.

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