There is much controversy over when to machine the rotors. Some technicians are of the opinion that rotors should be machined any time the pads are replaced. Others machine new rotors prior to installation (we don’t recommend this with DBA rotors). Some vehicle manufacturers recommend only turning the rotors if the thickness variations exceed 0.15mm / 0.006 inches. We will leave this decision to the technician.
What you need to know is that all DBA rotors can be machined successfully, as long as they are not machined to or below minimum thickness. This includes cross‐drilled and slotted rotors, and you may be asked this question by your customers.
The following points must be noted if DBA slotted or DBA Gold rotors need to be machined.
1. Machine the disc taking the finest cut using the slowest feed rate.
2. After machining, clean the disc with 240 grit emery on both surfaces (do this while the disc is still spinning)
3. Clean the disc surfaces with a solvent such as Acetone. Do not use any oil or silicon based solvents.
After machining, the gray residue on the face of the disc rotor is graphite. Without thorough cleaning, the graphite will act as a lubricant. It can cause noise, glazed pads and inefficient stopping from any type of brake pad.
Disc Brakes Australia