Turning drilled rotors

[Joe911]

Has anyone had success turning cross-drilled rotors? Any tips about what to ask for? I have heard stories of cutting tips braking off when the hole interrupts the cut. I will be sending them out to be done.
Thanks in advance, Joe Riley

[ruf-porsche]

Instead of turning them on a lathe you can have them reground on a surfacer.

[Nine9six]

Have them resurfaced as ruf-porsche indicated. The desired finish on a brake rotor comes from having them blanchard ground. It's a rough finish as far as grinding goes, but if done correctly, it keeps the rotor faces parallel to each other, as well as running true to locating surface.
The locating surface is aka the rotor mounting surface.

P.S. You could also have them turned, as long as the person knows which face the rotor must run parallel to. Ask me how I know. Yeah, I had to take mine back to explain it to the guy.

The intermittent cut from the cross drilled rotors will not damage a carbide turning tool with at least .0625 radius tip. Actually a larger radiused tool is preferred (.125) or larger in some instances.

The larger radiused tool allows a less abrupt introduction when feeding the tool across the cross drilled holes of the rotor, and more tool tip strength with the large radiused tip of the carbide cutting tool.

[Joe911]

Ruf-Porsche – “them reground on a surface”. I am not sure what this means – I can envision the back surface cut on a big stone like a cylinder head milling machine but what about the other surface. Where would I go and what to ask for? Is this something that a automotive machine shop would be able to do and know what I am asking for?

Nine9six. So they can be done on a traditional brake disc resurfacer using a cutter as long as the tip is of a certain type and this is one with a large radius. Will the traditional machine in a typical Porsche shop have different cutters?

[ruf-porsche]

See this attach website.

http://www.etoolcart.com/browseproducts/Disc-Brake-Rotor-Grinder-T-1074.HTML

Check to see if your local brake or auto supply store have this type of equipment for resurfacing rotors.

[Nine9six]

Originally posted by Joe911
Nine9six. So they can be done on a traditional brake disc resurfacer using a cutter as long as the tip is of a certain type and this is one with a large radius. Will the traditional machine in a typical Porsche shop have different cutters?

Joe911,
Yes, as long as the shop has a large radiused carbide cutting tool. (most of them do)
All shops who turn rotors should have several cutting tools.
As stated before, the correct method to resurface your rotors, is to have them "blanchard ground"
Any machine shop with a blanchard grinding machine should be able to help you out...

[Rufblackbird]

hmm, that rotor grinder looks cool, probably gives you the same finish that new rotors come in.

The last set of rotors I cut were cross drilled ones, and I didn't have a problem with them. I didn't go very fast, as I wasn't too sure if the tip would be able to handle the interrupted cuts if it was going too fast.

[mark_d_mcguire]

Although I have turned rotors on my trucks and street cars, I have never resurfaced rotors on my track cars.

Since you brought up cross-drilled, I'm assuming you are using them for track duty. I'm to cheap to buy something that fancy for the street.

Maybe it's because I service the brakes quite frequently, but they never seem to get uneven or grooved. If they get thin I replace them. The mass you take of with resurfacing helps dissapate heat and I can't see how turning them would actually lengthen usefull life.

Any thoughts?

[Nine9six]

Has anyone here ever seen glazed a rotor?
Has anyone here ever seen a grooved rotor?
Anyone here seen a rotor run outside its specified TIR limits?
Ever wonder why there are minimum rotor thicknesses stated in most manuals?
Whether you turn or grind a fresh surface on your rotors, dont most pad mfg. want a fresh surface to "bed" the pads to?