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Brake lathes are specialty machines that serve one purpose – smoothing and evening rotors so that the brake pad can maintain consistent contact during operation. We teach you how to use a brake lathe for both automatic and manual, and whether or not you should invest in one for your home shop.
How to Use an Automatic On-Car Brake Lathe
Automatic on-car brake lathes make quick work of machining brake rotors.
- Remove the brake pads. You’ll need to get the wheel off, first. Then, remove the slider bolt, pivot the brake caliper up, and slide out the brake pad.
- Install the hub adapter. The hub adapter will act as a proxy for the wheel while the brake disc is being cut by the lathe, providing real-time feedback and automatic adjustment.
- Connect the lathe to the hub adapter. Move the cutting head out of the way, and align the holes on the lathe with the dowel pin on the adapter. Tighten the large draw knob by hand. It should slide in easily, without being forced.
- Position the cutting head. Center the head so the cutting arms are straddling the rotor. Push the cutting head squarely and firmly into place and secure it with an Allen wrench.
- Set the shut-off cam. Turn the knob until the tips clear the outside edge of the rotor, then loosen the cam screw. Pull the cam back until it rests on the automatic shut-off switch.
- Compensate for run-out. Press the on/off switch to turn the motor on. Activate the automatic lateral run-out adjustment feature. Wait for confirmation on the screen that the disc is ready to be cut.
- Prepare to cut. Use the cut-depth knobs to adjust the position of the cutting head. Adjust the inside tool arm first, then the outside tool arm. Lock the arms in place. Turn the motor off and position the chip deflector around the rotor and cutting arms.
- Make the cut. Turn the motor back on. Engage the automatic feed. The cutting process may take a few minutes. When the cut is complete, the lathe will automatically shut off. Measure and record the new disc measurements.
- Match the other side. Follow the same procedure on the other side to ensure your brake discs perform evenly. You will need to rotate the machine upside down.
How to Use an Off-Car/Bench Brake Lathe
Off-car or bench brake lathes can also be used to machine rotors.
- Choose wisely. Look for a lathe with an arbor of at least one inch; with adapters, these lathes can handle most jobs. A variable-speed lathe will give you the most control.
- Remove the wheel and rotor from the car. Slide the rotor onto the lathe spindle.
- Position the cutter. Unlock the cutting head and position it so that the cutting arms straddle the rotor. Lock the cutting head in place. Turn the crank to bring the bits close to the rotor.
- Check for run-out. Use a dial indicator or perform a scratch test to establish how much run-out you’re dealing with. A warped rotor cannot be fixed through resurfacing, so if there is a significant run-out, you may need to replace the rotor.
- Set the depth of the cut. Start the lathe and set the speed. Run the bits forward until they are at the inner aspect of the braking surface. Adjust the bits to the depth of cut you desire.
- Make the cut. Move the cutting head across the braking surface skimming the bits along the surface and moving material from the surface of the rotor. Turn the lathe off.
Do You Need a Brake Lathe?
Rust on the rotor can cause pitting and surface unevenness, which may prevent the brake pad from doing its job, and brake lathes are often the only option other than replacing the rotor.
For this reason, brake lathes are commonly found in garages that specialize in brake work. There are two kinds of brake lathes, on-car and off-car. Both kinds cost thousands of dollars, and must be carefully maintained in order to stay in alignment.
A brake lathe is not a practical tool for most home garages. Let your mechanic make this expensive investment and save your home shop dollars for something else.
For a more versatile lathe, look at the best midi-lathes.
Brake lathes resurface brake discs to improve vehicle performance and delay rotor replacement. Automatic/on-car and manual/off-car versions are available. Unless you are a professional mechanic who specializes in brake work, a brake lathe is unlikely to be a smart investment.