Any flaws and imperfections that are on the surface of the brake disc could be dangerous and hazardous to the car. Often, the discs will get skimmed if imperfections such as rust, indents or other specks are on the surface.
Reasons to consider skimming also include a shuddering or squealing sound when applying the brakes, vibration and spongy brake pedals. These are uncomfortable and irritating factors that a person can sense whilst driving.
Before considering skimming, you have to make sure that the part is fit to go through the procedure. The disc has to be thick enough as more of the surface will be machined off, and if irreparable damage and wear has not occurred. The deeper the damage the more difficult it is to machine off. This is due to all the layers that have been damaged and need to be removed.
Instead of purchasing a brand new brake disc, skimming could be an affordable alternative option. It is cheaper and takes a short amount of time to do. The technique uses a specialised machine called a lathe. A lathe clamps the workpiece on the jaw and rotates whilst a moveable cutting tool cuts away surface layer by surface layer. This is a specialised lathe that automatically attaches itself to the hub of the wheel and measures less than the thickness of a hair before starting the cutting process.
Skimming can also be done on a separate machine detached from the car. It is the same lathe machine but the mechanic is more in control of the specifications. The tolerance number is slightly harder to get under manual settings unless the most recent model of the lathe is being used.
Anyone could consider the skimming process whenever they hear squealing, feel shuddering or vibration, or experience a spongy pedal. These could eventually cause wear that will eliminate the function of the brake disc entirely.
Mechanics and engineers have approved the technique and some might say that it is better than getting a brand new part. All brake discs can be skimmed at least once in their lifetime before needing to be replaced. Replacement occurs when the part has reached minimum thickness that is no longer standard.