How to tell if a disc needs machining (changing brakes)?

Hi. I know how to change the brake pads but how can i tell if i need to take the car to a mechanic to get the disc machined?How to tell if a disc needs machining (changing brakes)?
they should be machined to do the job right but if you didn't get any vibration in the brake pedal when coming to a stop with the old pads on more than likely the rotors aren't warped any and you can get away without machining them.How to tell if a disc needs machining (changing brakes)?
If the vehicle is relatively new ( less than 5 years old ) and the rotors show no obvious signs of %26quot;grooves%26quot;, then it will be OK.........beyond that time frame or if there are grooves in the metal, then a mechanic can use a micrometer to see the thickness of the metal and if the rotor can be turned or notHow to tell if a disc needs machining (changing brakes)?
Uneven wear on the disc surface or reduced surface area contact between disc and brake pads...

However, its not advisable to machine (unless certified expert).

These disc are specially heat treated to withstand high temperature during hard braking and if not properly heat treated after machining will cause warping on disc.How to tell if a disc needs machining (changing brakes)?
when you come to a stop, the brake petal will move sightly in and out, you will feel it through

you foot ! or you could mic them!How to tell if a disc needs machining (changing brakes)?
It's probably cheaper to buy a new disc unless it's a special. If there are ridges more than 0.5-1.0 mm deep then the disc needs skimmed or replaced.How to tell if a disc needs machining (changing brakes)?
I always have the rotors resurfaced when I change the brake pads. You want a true surface or the new pads will chatter.How to tell if a disc needs machining (changing brakes)?
I never do it unless the pedal pulses. The shops alway say %26quot;replace%26quot; but I never do, and dont have any issues, EVER!