Turning rotors on a shop lathe

It totally depends on how long you want you a "pad replacement" to last as well as how "hard" the new pads are.

I put cheap pads on everything and don't sweat .020" wear grooves.

I would rather replace $20 pads than $60 rotors.

If machine work is really required, don't remove any more material than what gets you to 0.010 or so.

New rotors after 100k miles are pretty much expected on new GM junk.

I don't recall the numbers but the spec is VERY tight. I think it's in the ten-thousandths. That's why the only way to get some rotors adequately "flat/parallel/zero runout" is to use an on the car lathe.

Brake lathes use a double bit setup to ensure absolutely consistent thickness. Any thickness variations as you would likely get with cutting the sides separately (unless you indicate them very carefully) will produce tremendous pedal pulsation.

I'd also think that getting the rotor true to the axle flange would be important. It would be better to make a jig that resembles that flange which can be mounted and trued in the lathe chuck. Once that is true, mount the rotor to that and then tuning it will bring its faces and the axle interface parallel.

"Paul Hovnanian P.E." wrote in news: snipped-for-privacy@hovnanian.com:

The very best explanation of brake pedal pulsation I have ever seen; includes precise instructions on rotor machining:

Note that SURFACE FINISH is as important as TRUENESS. Chain stores and clueless garages (dealer and independent) tend to forget that, keeping in service lathe bits that gall and tear more than machine.

Thanks. That's a good explanation of brake problems and repair procedures. However, I think this is written up assuming that the shop has the requisite adapters for turning rotors on a bench lathe. Based on the OP's post, I think he is going to try this on a shop (general purpose machinists) lathe. Particularly the bit about the 'chuck'.

"Paul Hovnanian P.E." wrote in news: snipped-for-privacy@hovnanian.com:

Well, the basic concepts should still be applicable even if the exact methods may differ, no?

Certainly. A dedicated brake lathe has special features to make the task easier, but a general purpose lathe can certainly do the job if you take the time with the dial indicator to ensure everything is running true before cutting.

Sorry.. I had intended to respond to this but thought better of it. You CAN set up a shop lathe to cut rotors.. Shop lathes, good ones, can do a lot.

It is a lot easier with at drum/rotor lathe.

Specifications of the cut can be found on the web.