MYTH DISPELLED - you CAN turn drilled rotors!
03-12-2008, 06:24 PM
#1
Three Wheelin'
Thread Starter
MYTH DISPELLED - you CAN turn drilled rotors!
I just got my truck brembo cross drilled rotors turned at a local tire shop! The tech told me that if you go slow and not take off too much material each pass it is no problem.
I know there are alot of people on the internet claiming it cant be done. Some shops will tell you that it cant be done. They are wrong! Just make sure that the rotor is thicker than minimum thickness. Some manufacturers recommend not exceeding 120% the minimum thickness for greater rotor life.
I also learned that Porsche is one of the few applications where the cross drilliing spirals out on the front wheels. My brembos and most other manufactures design rotor drilling that spiral in. Always follow manufacturer guidelines on which orientation is proper when installing new rotors.
With all this said, Ive never had good lifetime out of a rotor thats been turned, so I expect that Ill be buying new ones in the next 18-24 months, but it beats dropping $250 right now...
I know there are alot of people on the internet claiming it cant be done. Some shops will tell you that it cant be done. They are wrong! Just make sure that the rotor is thicker than minimum thickness. Some manufacturers recommend not exceeding 120% the minimum thickness for greater rotor life.
I also learned that Porsche is one of the few applications where the cross drilliing spirals out on the front wheels. My brembos and most other manufactures design rotor drilling that spiral in. Always follow manufacturer guidelines on which orientation is proper when installing new rotors.
With all this said, Ive never had good lifetime out of a rotor thats been turned, so I expect that Ill be buying new ones in the next 18-24 months, but it beats dropping $250 right now...
03-12-2008, 07:01 PM
#2
RL Technical Advisor
Speaking only for myself, I've always known it CAN be done, but I do question the wisdom of doing it in the first place. 
Removing mass from these relatively small rotors runs counterintuitive to me and I've never enjoyed any success by doing so despite what might appear to be a good idea.
Removing mass from these relatively small rotors runs counterintuitive to me and I've never enjoyed any success by doing so despite what might appear to be a good idea.
03-12-2008, 09:40 PM
#4
Super Moderator
Needs More Cowbell
Lifetime Rennlist
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Needs More Cowbell
Lifetime Rennlist
Member
Speaking only for myself, I've always known it CAN be done, but I do question the wisdom of doing it in the first place.
Removing mass from these relatively small rotors runs counterintuitive to me and I've never enjoyed any success by doing so despite what might appear to be a good idea.
Removing mass from these relatively small rotors runs counterintuitive to me and I've never enjoyed any success by doing so despite what might appear to be a good idea.
Just buy new rotors.
03-12-2008, 10:08 PM
#5
Rennlist Member
While yes its physically possible to turn them, I guess it depends on what you are correcting. Small slight grooves when the rotor is otherwise full thickness, I guess you would be ok. But the issue I always understood was you cannot have square edges to the hole, they have to be chamfer. By turning the rotor you are cutting off the chamfer, so you would then have to go back and re-chamfer the front and back of each hole, otherwise you are inviting stress cracks.
Just my 2 cents (maybe less)
Just my 2 cents (maybe less)
03-12-2008, 10:14 PM
#6
Instructor
I agree with Steve but if you must clean up your rotors I would grind them instead of turning. A horizontal rotary like a flywheel grinder or its industrial cousin Blanchard grinding have several advantages. It does not care that there are holes, and it can get just under the "skin" clean up the ridges with minimal material removal. You will also get that nice unidirectional grind pattern, just like new factory rotors.
I have never found a brake lathe to offers as true a surface or can keep as tight a control on run out. Traditionally they also need to take a bigger cut to get under the surface skin and will "wipe" some material into the holes. In practice an interuped cut will never produce as good of a surface as a continuos cut.
Engine machine shops that can grind flywheels can do the rotors but got to wonder at shop rates these days if it is really value added compared to just dropping the old rotor in the scrap pile and getting a fresh one that’s perfectly balanced and has no cracks starting out from the vent holes.
Side note. My new 993tt Zimmerman rotors now have chamfered cross-holes where previous sets did not. Since they get replaced often I never bothered to chamfer the holes on the new ones. It helps reduce the time it takes for the cracking to start but does not eliminate it. Maybe they were getting to many complaints on premature cracking.
Rick
I have never found a brake lathe to offers as true a surface or can keep as tight a control on run out. Traditionally they also need to take a bigger cut to get under the surface skin and will "wipe" some material into the holes. In practice an interuped cut will never produce as good of a surface as a continuos cut.
Engine machine shops that can grind flywheels can do the rotors but got to wonder at shop rates these days if it is really value added compared to just dropping the old rotor in the scrap pile and getting a fresh one that’s perfectly balanced and has no cracks starting out from the vent holes.
Side note. My new 993tt Zimmerman rotors now have chamfered cross-holes where previous sets did not. Since they get replaced often I never bothered to chamfer the holes on the new ones. It helps reduce the time it takes for the cracking to start but does not eliminate it. Maybe they were getting to many complaints on premature cracking.
Rick
03-13-2008, 12:05 AM
#7
Three Wheelin'
Thread Starter
Interesting notes on the chamfers. I just measured my truck rotors after turning and found that the chamfers are still there even when the rotors are close to theri minimum thickness (0.010" over min). Brembo made the rotors to have the chamfers all the way through minimum.
I agree that turning rotors is only temporary fix - typically lasting a year or so on other vehicles - but at $12/rotor for 12 months of use beats the heck out of $125 for the cost of a new one!
Honestly, I dont think Ill go drilled on my truck again. These "made in mexico" brembo rotors have been a big disappointment - lasting no longer than the cheap vatozone chinese rotors. However, my brembo rotors (OE?) on the 993 keep kicking butt.... What gives? Probably better weight balance and brake bias in the p-car!
I agree that turning rotors is only temporary fix - typically lasting a year or so on other vehicles - but at $12/rotor for 12 months of use beats the heck out of $125 for the cost of a new one!
Honestly, I dont think Ill go drilled on my truck again. These "made in mexico" brembo rotors have been a big disappointment - lasting no longer than the cheap vatozone chinese rotors. However, my brembo rotors (OE?) on the 993 keep kicking butt.... What gives? Probably better weight balance and brake bias in the p-car!
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03-13-2008, 06:49 AM
#8
Rennlist Member
I agree with Steve but if you must clean up your rotors I would grind them instead of turning. A horizontal rotary like a flywheel grinder or its industrial cousin Blanchard grinding have several advantages. It does not care that there are holes, and it can get just under the "skin" clean up the ridges with minimal material removal. You will also get that nice unidirectional grind pattern, just like new factory rotors..........
Rick
Rick
03-13-2008, 07:42 AM
#10
Race Car
Interesting notes on the chamfers. I just measured my truck rotors after turning and found that the chamfers are still there even when the rotors are close to theri minimum thickness (0.010" over min). Brembo made the rotors to have the chamfers all the way through minimum.
I agree that turning rotors is only temporary fix - typically lasting a year or so on other vehicles - but at $12/rotor for 12 months of use beats the heck out of $125 for the cost of a new one!
Honestly, I dont think Ill go drilled on my truck again. These "made in mexico" brembo rotors have been a big disappointment - lasting no longer than the cheap vatozone chinese rotors. However, my brembo rotors (OE?) on the 993 keep kicking butt.... What gives? Probably better weight balance and brake bias in the p-car!
I agree that turning rotors is only temporary fix - typically lasting a year or so on other vehicles - but at $12/rotor for 12 months of use beats the heck out of $125 for the cost of a new one!
Honestly, I dont think Ill go drilled on my truck again. These "made in mexico" brembo rotors have been a big disappointment - lasting no longer than the cheap vatozone chinese rotors. However, my brembo rotors (OE?) on the 993 keep kicking butt.... What gives? Probably better weight balance and brake bias in the p-car!
