First, one must decide if there is enough remaining material for reasonably proper function. Most of the "steel" drag brake rotors do not present adequate material thickness to permit anything more than a deglazing or a very minor cleanup cut. Remember, that automotive braking systems of this nature are designed around friction and heat production, and it is the responsibility of the rotor (disc brakes) to absorb this heat as produced, functioning as a heat-sink initially, before dispelling it into the atmosphere; and if your already overheating the disc now, this causing the resultant warpage, then how well do you think they're going to work after the removal of any significant sum of material?
I my opinion grinding is the best way of servicing the rotor, and I have cut them previously utilizing our flywheel grinder, this which is designed for just such types of items, and is the equipment I would advise in the attempt for a reasonably proper outcome.
As far as for the localized hardness formations, yes is a concern, and this will be very apparent upon the cutting process (even more so particularly if utilizing a lathe and cutting tool) and if excessive the subject part should be discarded, as not only will the coefficient of friction and effectiveness in the act of braking function be affected, but also significant ductility in the metal is lost and this could lead to a catastrophic failure!
Scott.
