Disk brake turning - Page 2
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  1. #21
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    Perry Harrington. He is a PM member.

  2. #22
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    Quote Originally Posted by rdhem2 View Post
    I need to help a buddy out by straightening up his disk brake rotors for his mini dragster. They are a odd size with a five hole mount pattern. In short not available any more. Dealer wants $378.00 ea to replace them. The rotors are next to new and have a maximum run out of less then .005". But are pitted and have rust bumps even after a glass bead spray.

    Who has the best procedure to do a simple turn on an engine lathe. Is grinding a solution? No local brake shops will touch them with no real reason given.
    Mini dragster rotors are little flat plate things, nothing like vented street car rotors. They start as plate, and are best flattened by Blanchard grinding. 5 minutes of research shows the most common 5 bolt mini dragster brake setup is made by Moser, and a new rotor from Jegs is $95.

    Moser Engineering 62-1: BRAKE ROTOR | JEGS

    Sent from my Pixel XL using Tapatalk

  3. #23
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    Quote Originally Posted by steve-l View Post
    I have noticed that with many new rotors they don't stay straight. Just after a couple of months use , they are warping. This issue is appearing across all brands, domestic and imported. This does not appear to be an issue (in my experience) with OEM parts. It has been impossible to tell where these rotors are being made, but I suspect China. I suspect the issue is excessive internal stresses left over from the casting process and with the heating and cooling from normal use the discs are stress warping. The argument of replacement being cheaper than turning is not so viable anymore. Has anyone else had this same experience?
    I had exactly the same experience. Some 30 years of it.

  4. #24
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    Quote Originally Posted by AlexO View Post
    I had exactly the same experience. Some 30 years of it.
    This is a much better explanation about the real "process" than I was able to do. It is common for most brake discs. To turn away the warping after a time, as I have described in a previous thread here, makes the discs better than new. You need to perform the cut with two bits, both sides of the disc in one operation. To mill one side at the time will not result in parallel surfaces good enough. Maybe you can grind, with a lot of cooling liquid, in a very good machine. There are special machines for such tasks, used for Aircraft brake discs. For the car brakes I know you would feel 0,002" out of parallelism, from the brake pedal and in the wheel.

  5. #25
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    Quote Originally Posted by cg285 View Post
    here is a slide show made by a brake pad manufacturer that has some VERY good information about turning rotors
    http://www.oeqf.com/techinfo/scratch...atching_lg.htm
    under tips and techniques i believe there is one small error where they say rotor thickness should not exceed .0003 which i believe should say .003
    (looking in a workhorse service manual it says exceeding .002)
    You are confusing thickness variation with runout. A thickness variation of .003 would make for very uncomfortable and dangerous braking

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  7. #26
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    Quote Originally Posted by POAx View Post
    This is a much better explanation about the real "process" than I was able to do. It is common for most brake discs. To turn away the warping after a time, as I have described in a previous thread here, makes the discs better than new. You need to perform the cut with two bits, both sides of the disc in one operation. To mill one side at the time will not result in parallel surfaces good enough. Maybe you can grind, with a lot of cooling liquid, in a very good machine. There are special machines for such tasks, used for Aircraft brake discs. For the car brakes I know you would feel 0,002" out of parallelism, from the brake pedal and in the wheel.
    You're absolutely right and I've done it last only a couple of months ago - fresh in my mind too. I was super careful - used a brand new hub to mount the disk in the chuck and skim the mounting face. Overall, I was within a couple of microns out of...whatever. The result was complete crap.

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    Most aftermarket rotors are made in China...and for the cost it's hard to see how they can do it.

    Just replaced the front rotors on my Nissan Titan truck, I used the most expensive non-Italian or non-Japanese rotors I could find - and they were only like $50 each. And that's for a big, fat, ventilated disk rotor with an anti-rust plating!

    So far the rotors are working perfectly, as much as I hate to, I have to give the Chinamen credit.

    In past years I have attempted to turn rotors using a new-condition cnc lathe...nope, they didn't work worth a damn, it's just too hard to get them located right for both front and back turning.

    ToolCat

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    Why all of the work ?

    Had a brake lathe in HS auto shop and many mobile brake services have portable units that turn the rotors while on the vehicle.

    This is old common stuff but we may be missing something.

    On local craigslist there usually are a couple on car machines and at a recent estate sale was a shop machine for drums and rotors.

    Seems like a lot of trouble to save a few bucks unless the normal sources of automotive machine work are not the re anymore.

    Sent from my SAMSUNG-SGH-I337Z using Tapatalk

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    Quote Originally Posted by digger doug View Post
    Seems like you got pretty good advice the first time you asked this. Why the new thread?

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    i must be lucky then, because everytime i did it on the lathe it turned out well.

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    Quote Originally Posted by LexD View Post
    You are confusing thickness variation with runout. A thickness variation of .003 would make for very uncomfortable and dangerous braking
    i only consider thickness variation

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    Quote Originally Posted by dian View Post
    i must be lucky then, because everytime i did it on the lathe it turned out well.
    I'd appreciate a description of how you did it - if you have the time. I tried to take all necessary precautions and I used an accurate lathe on which I made literary hundreds of laps up to 10" or so. For some reason though the disks measured well on the lathe ( within 3-5 microns ) they caused very irritating pedal pumping once on the car.

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    Thickness variation is only one thing on a disc brake.
    3 microns would be good, 5 maybe outside spec.
    Runout as mounted is so very important, surface finish is also.
    Lathes tend to leave a record player surface. The pad will climb the lines, hit a hard limit and "slap" back which results in a pulsing feeling at the pedal.
    The number one new car dealer warranty problem is pulsating brakes so a lot of money is spent trying to get it right.
    Simple and very cheap parts when produced in millions yet a big ass headache.
    Life as a engineer in charge of such products must suck.
    Bob

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    A friend of mine had me turn some aftermarket rear rotors for his racecar. EBC wanted quite a bit for a new set. I think they ended up within .002" in parallelism and he had no problems or fluttering going well over 100mph on Watkins Glenn. One tip, if you turn a rusty rotor get under the rust in one shot then come back out for your finish pass.

    Sent from my XT1053 using Tapatalk

  19. #35
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    Quote Originally Posted by Spyderedge View Post
    A friend of mine had me turn some aftermarket rear rotors for his racecar. EBC wanted quite a bit for a new set. I think they ended up within .002" in parallelism and he had no problems or fluttering going well over 100mph on Watkins Glenn. One tip, if you turn a rusty rotor get under the rust in one shot then come back out for your finish pass.

    Sent from my XT1053 using Tapatalk
    Rear rotor are more forgiving than front when it comes to errors in parellelism/thickness.

  20. #36
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    Quote Originally Posted by AlexO View Post
    I'd appreciate a description of how you did it - if you have the time. I tried to take all necessary precautions and I used an accurate lathe on which I made literary hundreds of laps up to 10" or so. For some reason though the disks measured well on the lathe ( within 3-5 microns ) they caused very irritating pedal pumping once on the car.
    My best guess would be that you did not indicate off the right surface, (hubless) drums/rotors typically indicate off the inner face and the pilot hole. Not trying to knock your machining, its just the nature of the work. I've turned thousands of drums/rotors in a BL with few comebacks, seen people doing it on engine lathes that indicate off wrong surface, no idea how you indicated. Just because it runs true on lathe does not mean it will run true on hub.

  21. #37
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    yes, i clean up the mounting surface first and go from there. sometimes i flip the disk, sometimes not. the only problem i have is vibrations. you have to get rid of them, otherwise finish will be no good. on my sports cars i go over the disk with a hone, usually on the cylindrical grinder.

    btw, i dont get the runout/thickness variation thing. if no runout, no thickness variation.

  22. #38
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    This is how I do them on the Colchester.


    MOV129 - YouTube

  23. #39
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    Slightly related
    With the price drop over the years of replacement rotors I stopped using the brake lathe or paying someone to do it
    I've noticed organic pads have a tendacy of glazing and "hot spotting" a rotor
    Since switching to ceramics many of the rotor issues have diminished
    Break in of pads and new rotors will definitely affect warpage potential

  24. #40
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    I would rather drop them off at NAPA for $40 then make a giant rusty mess on my lathe and in my shop.


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