There are three cases that cause brake rotors to need to be resurfaced/turned and/or replaced.
1.Gouging of the rotor by the brake pad holding mechanism (the pad were rubbed completely
away and the metal holding the pad start digging into the rotor)
2.Warping of the rotor from extreme use (rotor gets too hot and warps upon cooling)
3.The rotor itself wears down to a point that it is too thin and could possibly break when used
(this generally occurs when brake pads made of a material that is harder than the rotor
material and the rotor wears down instead of the brake pad)
So you’ve been researching having your messed-up brakes replaced, and are wondering if you could just get your rotors resurfaced instead to save a little money. Brake rotor resurfacing is when a mechanic or technician uses a lathe (or sends them somewhere to get laithed) to grind down your existing brake rotors and even out the run-out to get you a little more mileage before replacing them. So is it worth it to have this service provided? Should you resurface your rotors, or have them replaced? Let’s take a look.
You definitely need to get them resurfaced if they are warped or damaged. Usually you can feel if they are warped through the brake pedal when stopping -- instead of a smooth stop it will kind of vibrate or pulsate when braking at higher speeds. It's very noticeable. This can be measured with a dial gauge and checked against the repair manual's recommendations for "runout". You will need a dial gauge, and some sort of a mount to hold the gauge steady while you spin the rotor.
Before having a damaged or warped set of rotors turned, check their thickness. If they're close to the minimum, resurfacing them will leave you with rotors that are too thin. If you're at this point, you should have rotors that are thick enough and not damaged. Many people recommend resurfacing of them so the pads and rotors can better mate and wear into each-other. We at Qualls Auto Salvage tend to agree with this!