Turning Rotors

[nc211]

Question: And this might be the dumb one of the week. Can slotted and drilled rotors be turned? Thinking of buying some, but want to make sure you can service them later on.

Thanks all!

[dcfish]

Question: And this might be the dumb one of the week. Can slotted and drilled rotors be turned? Thinking of buying some, but want to make sure you can service them later on.

Thanks all!

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I think you can turn them you would just lose some of the slot and it's ability to throw out the brake dust and maybe a little effectiveness of the slots purpose.

[LScott400]

Yes, machining slotted and drilled rotors is no problem. The difficulty in turning any rotor is that there is so little margin for wear anymore. There are 3 specifications for rotors. Nominal (new), Machine To and Discard thickness. The Discard spec is a safety/legal liability measurement at which a brake failure may occur. The "Machine To Thickness" is the thinnest measurement at which the rotor will have enough margin for wear with a new set of pads to remain above the Discard spec.

The idea of machining is to have a perfect surface for the new pad to seat and burnish in quickly. Personally, I have given up turning rotors. If they are scored and have any wear they are unlikely to be in spec after turning. I would rather have as much metal mass for dissipating heat (thus better braking) as possible. The downside is possible brake noise. I avoid this by using a sanding disc to put a non-directional finish on the rotor and using only OE brake pads.

[SKperformance]

Drilled or slotted rotors are not meant to be turned.

If they are they end up causeing wear and damage on the carbide tips of the machines from the sharp peaks and edges.

It can be done as i have done them myself once when i was jobless.

Otherwise just buy new rotors it is safer and cheaper in the overall as a machined rotor just warps faster as it is uneven amounts of metal causing non uniform expansion of metal which was the reason why the rotors warped in the first place.

[dcfish]

Drilled or slotted rotors are not meant to be turned.

If they are they end up causeing wear and damage on the carbide tips of the machines from the sharp peaks and edges.

It can be done as i have done them myself once when i was jobless.

Otherwise just buy new rotors it is safer and cheaper in the overall as a machined rotor just warps faster as it is uneven amounts of metal causing non uniform expansion of metal which was the reason why the rotors warped in the first place.

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SK, Best advice, I agree with the buying new rotors rather than turning.

[Kennyr]

You only turn rotors on American junk. My experience and opinion only. You can buy aftermarket Lexus rotors pretty darn cheap. Carquest has them for almost free.

[91L3xus]

$150 for 4 slotted and drilled rotors for my '91 on eBay. Amazing.

[mehullica]

Once again, the rotor warp theory. Rotors don't warp. Friction is the mechanism that converts dynamic energy into heat. Just as there are two sorts of friction between the tire and the road surface (mechanical gripping of road surface irregularities by the elastic tire compound and transient molecular adhesion between the rubber and the road in which rubber is transferred to the road surface), so there are two very different sorts of braking friction - abrasive friction and adherent friction. Abrasive friction involves the breaking of the crystalline bonds of both the pad material and the cast iron of the disc. The breaking of these bonds generates the heat of friction. In abrasive friction, the bonds between crystals of the pad material (and, to a lesser extent, the disc material) are permanently broken. The harder material wears the softer away (hopefully the disc wears the pad). Pads that function primarily by abrasion have a high wear rate and tend to fade at high temperatures. When these pads reach their effective temperature limit, they will transfer pad material onto the disc face in a random and uneven pattern. It is this "pick up" on the disc face that both causes the thickness variation measured by the technicians and the roughness or vibration under the brakes reported by the drivers.

With adherent friction, some of the pad material diffuses across the interface between the pad and the disc and forms a very thin, uniform layer of pad material on the surface of the disc. As the friction surfaces of both disc and pad then comprise basically the same material, material can now cross the interface in both directions and the bonds break and reform. In fact, with adherent friction between pad and disc, the bonds between pad material and the deposits on the disc are transient in nature - they are continually being broken and some of them are continually reforming

[SRK]

Once again, the rotor warp theory. Rotors don't warp. Friction is the mechanism that converts dynamic energy into heat. Just as there are two sorts of friction between the tire and the road surface (mechanical gripping of road surface irregularities by the elastic tire compound and transient molecular adhesion between the rubber and the road in which rubber is transferred to the road surface), so there are two very different sorts of braking friction - abrasive friction and adherent friction. Abrasive friction involves the breaking of the crystalline bonds of both the pad material and the cast iron of the disc. The breaking of these bonds generates the heat of friction. In abrasive friction, the bonds between crystals of the pad material (and, to a lesser extent, the disc material) are permanently broken. The harder material wears the softer away (hopefully the disc wears the pad). Pads that function primarily by abrasion have a high wear rate and tend to fade at high temperatures. When these pads reach their effective temperature limit, they will transfer pad material onto the disc face in a random and uneven pattern. It is this "pick up" on the disc face that both causes the thickness variation measured by the technicians and the roughness or vibration under the brakes reported by the drivers.

With adherent friction, some of the pad material diffuses across the interface between the pad and the disc and forms a very thin, uniform layer of pad material on the surface of the disc. As the friction surfaces of both disc and pad then comprise basically the same material, material can now cross the interface in both directions and the bonds break and reform. In fact, with adherent friction between pad and disc, the bonds between pad material and the deposits on the disc are transient in nature - they are continually being broken and some of them are continually reforming

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Did you by any chance pass up a career in the aerospace industry? You should have been a rocket scientist.

That little myth about rotors not warping has been floating around the internet for a while now. My advice would be to write the makers of brake lathes and tell them that their machines serve no purpose. And tell any automotive machinist you can make stand still long enough to listen to you that "rotors don't warp" and that all of the run-out and hollow spots and multiple variations they have seen are not warps but this little "friction depost" theory you have believed so well.

OEM and aftermarket brake part manufacturers spend a lot of time trying to develop alloys and cooling pathways in rotors to prevent warping. Some are successful, and others are not. But it is an established fact that warping (lateral run-out) occurs in brake discs or rotors.

[nc211]

Thanks guys!

I think I'm just going to stick with oem brakes from now on, or at least try too "wallet plays main factor". The slotted rotors looks cool, and I'm sure they're awesome rotors, but for me, I just don't think I need them.

[crazyls]

http://www.stoptech.com/whitepapers/warped_rotors_myth.htm

interesting? whats the truth man!

[nc211]

Ok, well here is my question: I read that article, and I will or will not argue the "warped" debate. To me, warped seems like a logical way to describe the problem. Anyone who has driven in the winter months, heated up the brakes pretty badly and then hit a slush puddle of icy cold water knows what that can do. But, according to that article, by me pulling into my driveway while applying my brakes to slow down "effectively heating them up" and then instantly using my e'brake to keep my car on the hill, will not allow the surface to cool back down. This should create the brake pad imprint. But my rotors don't have that imprint. However, picture 3 in that article seems to be the best way to describe my brakes. So, is using the e-brake a bad thing? My house is on a steep hill, and there is no way my tranny will hold the car on the hill all the time.