Re: Turning Rotors: a case study...
 

doug wrote:
>>sorry - unless this disk has been operated well into red heat, you're
>>not going to get much change in microstructure. you can however have
>>problems with a bad disk if it was not heat treated properly after
>>casting. when operated hot, /that/ disk will distort. more likely is
>>that there are simply different cooling rates on different parts of the
>>disk leading to local temporary distortion. that shouldn't happen on a
>>disk of sufficient thickness and whose internal vanes have not lost too
>>much material through rust.
>
>
> Your opinion and a dollar will get you a cup of coffee. That's all it's
> worth . Repeated heating and cooling cycles will definitely change the
> distribution of carbon atoms in an iron matrix - and it doesn't have to be
> "red" hot. The temperatures created by the crappy pads used by GM did the
> job in less than 15,000 miles.

diffusion, the migration of carbon atoms in the iron matrix, happens
well below red heat. but /significant/ diffusion, recrystallization,
graphite flake/nodule growth, or other phase changes, doesn't. and if
you're trying to argue that a brake disk is martensitic, you need to
think again.

if your gm disk warps in 15k, you need to consider other factors. for
honda, elastic distortion caused by incorrect wheel lug torquing has a
huge influence. but if it's the disk alone, things like bad
post-casting heat treatments, uneven material thickness, etc. can
influence whether a disk stays true at high temperatures. the most
likely item is cutting corners on heat treatment and reducing heat soak
time.

my money's on incorrect lug torquing.

>
>>my experience is that the disk cutting process is far from perfect - those
>>cutting machines see heavy usage, and you can mount the same disk up a
>>dozen times and get 13 different centers.
>>
>
> If that's your experience, that's too bad. You need to find a better
> technician, or learn to do it yourself.

i was a vehicle mechanic for 5 years and also have a materials degree.
is that good enough?

Re: Turning Rotors: a case study...
 

================================================== ============
TOPIC: Turning Rotors: a case study...
http://groups.google.com/group/alt.a...594af6aa37ae67
================================================== ============

> == 1 of 2 ==
> Date: Wed, Dec 28 2005 7:43 am
> From: jim beam
>
> karl wrote: [Date: Sat, Dec 17 2005 9:20 pm]
> > > == 4 of 6 ==
> > > Date: Sat, Dec 17 2005 8:41?am
> > > From: jim beam?
> >
> > snip
> >
> > > you can mount the same disk
> > > up a dozen times and get 13 different centers.
> >
> >
> > and
> >
> >
> > > == 6 of 6 ==
> > > Date: Sat, Dec 17 2005 9:02?am
> > > From: jim beam
> >
> > snip
> >
> > > i used to work in a shop and had access - that's how i
> > > know these things can be difficult to center, giving
> > > inconsistent results.
> >
> >
> >
> >
> > Why bring up coaxiality, or lack thereof? It is
> > irrelevant as long as the contact surface with the
> > pad gets machined.
> >
> > Relevant is that the machined surface and the
> > mounting surface are perpendicular to the axis, and
> > it is therefor important that the mounting surfaces
> > are clean. This is the area you have to concentrate
> > on, not centering. No wonder why you got
> > "inconsistent results."
> >
> you need to read around a bit more. if the disk plane
> is not exactly perpendicular to the rotation axis, on
> a floating [single piston] caliper, you have pulsing
> in the hydraulics because of momentum differences due
> to the mass of the caliper vs. the piston. with a
> fixed caliper and 2 [or 4 or 6] pistons, the mass on
> each side is the same and there's little net effect.


In two messages you wrote that "centering" the disks is
important, and if this is not done properly it will give
"inconsistent results." This is what I was responding
to. Can you read? The relevant excerpts are right here.
(I had written "coaxiality" when I meant centricity. I
have corrected this already.)

Correcting you, I wrote, "Relevant is that the machined
surface and the mounting surface are perpendicular to
the axis." Can you read? You do not "need to read around
a bit more," it's right here.

Pulsing "because of momentum differences due to the
mass of the caliper vs. the piston," and "the mass on
each side is the same and there's little net effect."
Rubbish!

Re: Turning Rotors: a case study...
 

"jim beam" <nospam@example.net> wrote in message
news:W5edneEaDO3cKS_enZ2dnUVZ_v6dnZ2d@speakeasy.ne t...
> doug wrote:
>>>sorry - unless this disk has been operated well into red heat, you're
>>>not going to get much change in microstructure. you can however have
>>>problems with a bad disk if it was not heat treated properly after
>>>casting. when operated hot, /that/ disk will distort. more likely is
>>>that there are simply different cooling rates on different parts of the
>>>disk leading to local temporary distortion. that shouldn't happen on a
>>>disk of sufficient thickness and whose internal vanes have not lost too
>>>much material through rust.
>>
>>
>> Your opinion and a dollar will get you a cup of coffee. That's all it's
>> worth . Repeated heating and cooling cycles will definitely change the
>> distribution of carbon atoms in an iron matrix - and it doesn't have to
>> be "red" hot. The temperatures created by the crappy pads used by GM did
>> the job in less than 15,000 miles.
>
> diffusion, the migration of carbon atoms in the iron matrix, happens
> well below red heat. but /significant/ diffusion, recrystallization,
> graphite flake/nodule growth, or other phase changes, doesn't. and if
> you're trying to argue that a brake disk is martensitic, you need to
> think again.
>
> if your gm disk warps in 15k, you need to consider other factors. for
> honda, elastic distortion caused by incorrect wheel lug torquing has a
> huge influence. but if it's the disk alone, things like bad
> post-casting heat treatments, uneven material thickness, etc. can
> influence whether a disk stays true at high temperatures. the most
> likely item is cutting corners on heat treatment and reducing heat soak
> time.
>
> my money's on incorrect lug torquing.
>
>>
>>>my experience is that the disk cutting process is far from perfect -
>>>those cutting machines see heavy usage, and you can mount the same disk
>>>up a dozen times and get 13 different centers.
>>>
>>
>> If that's your experience, that's too bad. You need to find a better
>> technician, or learn to do it yourself.
>
> i was a vehicle mechanic for 5 years and also have a materials degree.
> is that good enough?
>

Apparently not - it hasn't helped you to do the job correctly. Like I said
before, there's one in every group. Although Dave Kelsen may once again take
issue with that.

Re: Turning Rotors: a case study...
 

karl wrote:
<snip>
> Pulsing "because of momentum differences due to the
> mass of the caliper vs. the piston," and "the mass on
> each side is the same and there's little net effect."
> Rubbish!
>

really? why? i'd love to see your explanation.

Re: Turning Rotors: a case study...
 

doug wrote:
> "jim beam" <nospam@example.net> wrote in message
> news:W5edneEaDO3cKS_enZ2dnUVZ_v6dnZ2d@speakeasy.ne t...
>
>>doug wrote:
>>
>>>>sorry - unless this disk has been operated well into red heat, you're
>>>>not going to get much change in microstructure. you can however have
>>>>problems with a bad disk if it was not heat treated properly after
>>>>casting. when operated hot, /that/ disk will distort. more likely is
>>>>that there are simply different cooling rates on different parts of the
>>>>disk leading to local temporary distortion. that shouldn't happen on a
>>>>disk of sufficient thickness and whose internal vanes have not lost too
>>>>much material through rust.
>>>
>>>
>>>Your opinion and a dollar will get you a cup of coffee. That's all it's
>>>worth . Repeated heating and cooling cycles will definitely change the
>>>distribution of carbon atoms in an iron matrix - and it doesn't have to
>>>be "red" hot. The temperatures created by the crappy pads used by GM did
>>>the job in less than 15,000 miles.
>>
>>diffusion, the migration of carbon atoms in the iron matrix, happens
>>well below red heat. but /significant/ diffusion, recrystallization,
>>graphite flake/nodule growth, or other phase changes, doesn't. and if
>>you're trying to argue that a brake disk is martensitic, you need to
>>think again.
>>
>>if your gm disk warps in 15k, you need to consider other factors. for
>>honda, elastic distortion caused by incorrect wheel lug torquing has a
>>huge influence. but if it's the disk alone, things like bad
>>post-casting heat treatments, uneven material thickness, etc. can
>>influence whether a disk stays true at high temperatures. the most
>>likely item is cutting corners on heat treatment and reducing heat soak
>>time.
>>
>>my money's on incorrect lug torquing.
>>
>>
>>>>my experience is that the disk cutting process is far from perfect -
>>>>those cutting machines see heavy usage, and you can mount the same disk
>>>>up a dozen times and get 13 different centers.
>>>>
>>>
>>>If that's your experience, that's too bad. You need to find a better
>>>technician, or learn to do it yourself.
>>
>>i was a vehicle mechanic for 5 years and also have a materials degree.
>>is that good enough?
>>
>
>
> Apparently not - it hasn't helped you to do the job correctly. Like I said
> before, there's one in every group. Although Dave Kelsen may once again take
> issue with that.
>
>

so why don't you make a technical rebuttal? share your superior
knowledge.

Re: Turning Rotors: a case study...
 

It took you 12 days to come up with your lame-ass text book reply. Yet you
still don't get it - you're trying to argue a point that many people have
already demonstrated to you that you are wrong about. I can't be bothered to
repeat their - and my - valid examples and explanations. Perhaps if you took
the time to review the threads in this post and you might begin to
understand what I mean. I doubt it, but you never know. As I said, you ARE
the one.

"jim beam" <nospam@example.net> wrote in message
news:icSdnRvqXdKE4ineRVn-pg@speakeasy.net...
> doug wrote:
>> "jim beam" <nospam@example.net> wrote in message
>> news:W5edneEaDO3cKS_enZ2dnUVZ_v6dnZ2d@speakeasy.ne t...
>>
>>>doug wrote:
>>>
>>>>>sorry - unless this disk has been operated well into red heat, you're
>>>>>not going to get much change in microstructure. you can however have
>>>>>problems with a bad disk if it was not heat treated properly after
>>>>>casting. when operated hot, /that/ disk will distort. more likely is
>>>>>that there are simply different cooling rates on different parts of the
>>>>>disk leading to local temporary distortion. that shouldn't happen on a
>>>>>disk of sufficient thickness and whose internal vanes have not lost too
>>>>>much material through rust.
>>>>
>>>>
>>>>Your opinion and a dollar will get you a cup of coffee. That's all it's
>>>>worth . Repeated heating and cooling cycles will definitely change the
>>>>distribution of carbon atoms in an iron matrix - and it doesn't have to
>>>>be "red" hot. The temperatures created by the crappy pads used by GM did
>>>>the job in less than 15,000 miles.
>>>
>>>diffusion, the migration of carbon atoms in the iron matrix, happens
>>>well below red heat. but /significant/ diffusion, recrystallization,
>>>graphite flake/nodule growth, or other phase changes, doesn't. and if
>>>you're trying to argue that a brake disk is martensitic, you need to
>>>think again.
>>>
>>>if your gm disk warps in 15k, you need to consider other factors. for
>>>honda, elastic distortion caused by incorrect wheel lug torquing has a
>>>huge influence. but if it's the disk alone, things like bad
>>>post-casting heat treatments, uneven material thickness, etc. can
>>>influence whether a disk stays true at high temperatures. the most
>>>likely item is cutting corners on heat treatment and reducing heat soak
>>>time.
>>>
>>>my money's on incorrect lug torquing.
>>>
>>>
>>>>>my experience is that the disk cutting process is far from perfect -
>>>>>those cutting machines see heavy usage, and you can mount the same disk
>>>>>up a dozen times and get 13 different centers.
>>>>>
>>>>
>>>>If that's your experience, that's too bad. You need to find a better
>>>>technician, or learn to do it yourself.
>>>
>>>i was a vehicle mechanic for 5 years and also have a materials degree.
>>>is that good enough?
>>>
>>
>>
>> Apparently not - it hasn't helped you to do the job correctly. Like I
>> said before, there's one in every group. Although Dave Kelsen may once
>> again take issue with that.
>
> so why don't you make a technical rebuttal? share your superior
> knowledge.

Re: Turning Rotors: a case study...
 

karl wrote:
<snip>
> Pulsing "because of momentum differences due to the
> mass of the caliper vs. the piston," and "the mass on
> each side is the same and there's little net effect."
> Rubbish

jim beam wrote:

>>really? why? i'd love to see your explanation

Karl - he's not worth the time or effort to try and discuss this with. But I
think you already know this ;-)

doug