The Flex-Hone for Rotors comes in coarse, medium and fine grits depending on the desired final surface finish. Although the coarse finish may work well to remove heavy buildup and corrosion, it leaves a relatively rough finish. In addition, the coarse grit can also take out the sharp edges on slots and cross-drilled holes. By removing these sharp edges, the rotors are much less prone to cracking from those machined areas.
Our process involved using all three grits in order from coarse to fine to reach a like-new surface finish. However, the medium grit will probably be strong enough to knock off the old transfer layer of pad material. This will create a fresh surface for the pads to bed into properly. As the grinding puts lots of iron particulates in the air, be sure to wear a facemask and safety glasses.
The set of test rotors we used came from a road-race car with a few track days worth of abuse. All four rotors featured a smooth, shiny surface with light circumferential grooving. While the instructions recommend users to attach the rotor securely to a brake lathe, we recognize that most people don’t have a lathe at home. Instead, we decided to remove the rotors from the vehicle and place them on a workbench. With our drill charged up and the coarse grit attached, we began honing away on the rotor. To achieve a consistent finish, the Flex-Hone head must stay square and flat against the rotor. Be sure to have at least a 50-percent overlap between passes to ensure that no rough or untouched edges remain. Use light, uniform pressure and keep the tool moving across the surface of the rotor.
After we finished removing the old transfer layer and exposed a new surface, we swapped out the coarse grit for medium grit. Working our way around the rotor using the same method as before, we kept honing until none of the marks left by the coarse grit were visible. Once no coarse marks remain, we switched to fine grit and remove any marks left by the medium grit attachment. This process will leave a finish very similar to a new rotor.