Accurate control of rotor tolerance is necessary for proper performance of the disc brakes. Machining of rotors should be done only with precision equipment.

All brake rotors have a minimum thickness dimension cast into them. This dimension is the minimum wear dimension and not a refinish dimension. Do not use a brake rotor that does not meet the specifications as shown in the specifications at the beginning of this section.

If rotors are removed, remove rust and scale from the rotor/hub and rotor/wheel mating surfaces. Failure to do so can cause excessive lateral runout when the rotor is mounted on the brake lathe or when the rotor is installed to the hub.

When refinishing rotors, always use sharp cutting inserts (bits, tips). Dull or worn inserts leave a poor surface finish which will affect braking performance. Make sure the brake lathe is clean and free of debris before turning rotors. Remove metal filings from the mating surface between the lathe and the cutting assembly. Remove filings from behind the tool bit holders.

Some brake lathes (Accu-turn or equivalent) can refinish a rotor's surface with one cut, regardless of the depth. However, the rotor must not vibrate during the refinishing operation. Use the vibration damping devices provided with the lathe.

Manufacturers of brake lathes that cannot control rotor vibration during deep cuts recommend several cuts to achieve the desired finish. Following the instructions provided with the lathe will help ensure high-quality machining. Again, always use the vibration dampening devices provided with the lathe.

Regardless of the brake lathe used, a shallow finish cut will not yield the best surface finish. A shallow cut of 0.05  mm (0.002 in) smears the rotor's surface, creating a rougher-than-desired finish. Cutting at least 0.127 mm (0.005 in) (per side) will leave a smoother surface, resulting in better brake performance.

Make sure to use the proper cutting inserts. use the cutting inserts recommended by the brake lathe's manufacturer. Check the cutting inserts' condition regularly. Replace them at the first sign of inferior refinishing. Following all the lathe's machining instructions will facilitate acquiring the desired surface finish.

All brake lathes use a single-point cutting tool. This tool will not yield the necessary surface finish. A secondary finishing operation must be performed. To obtain the necessary finish, follow this procedure: With the rotor turning in the brake lathe, sand each side of the rotor for a minimum of 90 seconds with 150 grit sand paper mounted on a sanding block. Use moderate pressure. After sanding, clean the rotor thoroughly. Use Saturn Brake Cleaner P/N 21007432 (or equivalent).

Caution: The surface finish quality of a machined rotor should be as high as a new rotor. Failure to obtain this best possible rotor surface finish will negatively affect braking performance.

Notice: Rotors or drums should always be replaced if machining results in a rotor or drum that does not meet the manufacturer's specifications for minimum rotor thickness or maximum drum diameter.

When installing new brake rotors, do not refinish the surfaces as these parts are at the correct level of surface finish.

A brake rotor is a precision machined part. It must be properly machined to provide proper service.

1. All rust and corrosion must be removed from the mounting surfaces of the rotor. Use a wire brush or a wire wheel and a drill to remove all corrosion and scale from the mounting surfaces of the rotor.

Any attempt to remachine a rotor must result in a surface finish equal to the quality of a new rotor. Failure to obtain this best possible rotor surface finish will negatively affect braking performance.

2. Make sure the correct bell clamps are used to mount the brake rotor on the brake lathe. Some bell clamps may appear to fit flush inside the brake rotor, but actually they may be too large, forcing the brake rotor to wobble when it turns on the lathe. The bell clamp outside diameter (D) must be less than 139 mm (5.47 in). If a brake rotor does not turn on a plane that is parallel to the brake lathe's cutting tip, lateral runout will be machined into the brake rotor.



3. Both surfaces of the inside bell clamp must be parallel or the rotor will not turn on a parallel plane with the cutting tip. If a bell clamp is dropped or damaged in any way, contact the brake lathe's manufacturer to obtain a new bell clamp.



4. Use the largest possible spacers (1) to hold the  bell clamps (2) on the lathe's spindle. This makes sure that there is the most mass possible on the spindle, helping the rotor to turn on a parallel plane with the brake lathe's cutting tip.
5. Use a magnetic dial indicator base and a dial indicator with graduations of 0.0001 inch (0.002 mm) to make sure that the rotor turns squarely on the brake lathe. Attach the dial indicator on the lathe and check rotor runout. Mark the highest point of lateral runout on the rotor. Loosen the attachment hardware and rotate the rotor 180 degrees while holding the inside  bell clamp (2) in its original position. Tighten attachment hardware and recheck rotor runout. Any runout must follow the rotor. The marked high spot must remain the high spot. If not, some problem exists in the attachment of the rotor on the lathe, such as bent bell clamps, incorrect bell clamps, or untrue mounting surfaces.
6. Visually check the machined rotor's surface finish. Any deterioration in surface finish quality usually indicates worn cutting tips. Always use cutting tips recommended by the brake lathe manufacturer.
7. A secondary finishing operation improves rotor surface finish. Some brake lathe manufacturers offer lathe-mounted tools for this purpose. If no such tool is available, Saturn recommends using silicon carbide 150 grit emery paper mounted on a sanding block. Using moderate pressure, hold paper against the rotor as it turns in the lathe for 90 seconds per side.
8. Thoroughly clean machined rotors with a spray solvent such as Saturn Choke and Brake Cleaner, or equivalent.