Michael Pardee wrote:
> "jim beam" <nospam@example.net> wrote in message
> newsq6dnWz14uq5Uz_eRVn-qA@speakeasy.net...
>
>>Stephen H wrote:
>>
>>>You may have had problems, and in a perfect world everyone would replace
>>>parts with new when worn with high quality stuff, but many want it done
>>>cheap.
>>>
>>>Anyway my point was to show how little metal comes off during a lathe
>>>job.
>>>
>>>
>>>
>>
>>i have two points:
>>
>>1. it ain't cheap enough to be worth bothering with [unless it's a disk
>>that requires complete disassembly of the hub] AND
>>
>>2. the results frequently aren't good enough to be worth the trouble. in
>>fact it often /causes/ problems.
>>
>>i'd much rather live with a slightly scored disk than one that's been
>>machined wrong and is now ruined.
>
>
> I don't think this issue can be resolved into a single best course of
> action. In another recent thread the subject of professional standards vs
> DIY standards came up, and I think that applies here. A DIYer who routinely
> leaves untouched disks that look good and have performed well is frugal and
> smart. A shop that routinely leaves untouched any disk is being sloppy.
>
> Jim, I gather you and I are on the same page on the DIY way of doing it. If
> the disks are serviceable as-is there is no point in doing anything to them
> except a quick wash with brake cleaner when we get our mitts off them. If
> they need more, replacement is the way to go. If we had free access to a
> lathe we might do the same as Stephen does - clean the surface up. Or maybe
> not.
>
> Mike
>
>
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.

 

> 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.
>
> 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.

 

Ahhh, New equipment.... Some are sweet!


--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist

http://autorepair.about.com/cs/troub...l_obd_main.htm
http://www.troublecodes.net/technical/


>> Mike
> 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.

 

> == 1 of 6 ==
> Date: Sat, Dec 17 2005 3:54 am
> From: Eric
>
> Stephen H wrote:
>
> > > I'm confused. You just told us that you took 0.004" of material off
> > > the rotor, but your initial and final thicknesses only vary by 0.001"?
> >
> > Because the rotor wasn't true-- the outside edge was thinner than the
> > inside edge, so only 001 was removed from the outside.
> >
>
> That's what I suspected, i.e., a lack of parallelism.
> Thanks for confirming it.



Thanks for "confirming" suspicion of lack of parallelism
are superfluous - Stephen H had told us of it:


> Date: Thurs, Dec 15 2005 4:48 am
> From: "Stephen H"
snip
> The left front rotor measured at .697 on the outside
> edge and .703 at the inside edge to start

 

> == 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."

 

> Date: Sat, Dec 17 2005 6:21 pm
> From: doug
>
> > Date: Sat, Dec 17 2005 8:41 am
> > From: jim beam
snip
> > 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.


Actually, he is talking about himself. He does not
understand the physical relationship between runout (I
believe this is the name - I am no mechanic) and
perpendicularity of axis and contact surfaces - he
concentrated on irrelevant coaxiality!:


> 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.

 

> Date: Sat, Dec 17 2005 9:20 pm
> From: "karl"
>
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."


In a number of messages (maybe in all of his "cutting
rotor" messages) jim beam emphasized the importance of
centering the disks when their surfaces are being
machined. This is what I was replying to - centering,
within limits, is irrelevant, but I used the wrong term
"coaxiality." Once again, important is the
"perpendicularity of axes and contact surfaces," and
anything that throws this off will cause problems.

In fact, there is the possibility that jim beam, too, is
talking about this when he writes about the importance of
centering: in a message at another list he wrote of the
importance of cleaning the mounting surfaces of the lathe
and of the disk.

 

> Date: Sat, Dec 17 2005 10:15 pm
> From: "karl"
>
> > Date: Sat, Dec 17 2005 6:21?pm
> > From: doug
> >
> > > Date: Sat, Dec 17 2005 8:41?am
> > > From: jim beam
> snip
> > > 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.
> >
snip
>
> Actually, he is talking about himself. He does not
> understand the physical relationship between runout (I
> believe this is the name - I am no mechanic) and
> perpendicularity of axis and contact surfaces - he
> concentrated on irrelevant coaxiality!:


In a number of messages (maybe in all of his "cutting
rotor" messages) jim beam emphasized the importance of
centering the disks when their surfaces are being
machined. This is what I was replying to - centering,
within limits, is irrelevant, but I used the wrong term
"coaxiality." Once again, important is the
"perpendicularity of axes and contact surfaces," and
anything that throws this off will cause problems.

In fact, there is the possibility that jim beam, too, is
talking about this when he writes about the importance of
centering: in a message at another list he wrote of the
importance of cleaning the mounting surfaces of the lathe
and of the disk.

 

karl wrote:
>> Date: Sat, Dec 17 2005 10:15 pm
>> From: "karl"
>>
>>> Date: Sat, Dec 17 2005 6:21?pm
>>> From: doug
>>>
>>>> Date: Sat, Dec 17 2005 8:41?am
>>>> From: jim beam
>> snip
>>>> 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.
>>>
> snip
>>
>> Actually, he is talking about himself. He does not
>> understand the physical relationship between runout (I
>> believe this is the name - I am no mechanic) and
>> perpendicularity of axis and contact surfaces - he
>> concentrated on irrelevant coaxiality!:
>
>
> In a number of messages (maybe in all of his "cutting
> rotor" messages) jim beam emphasized the importance of
> centering the disks when their surfaces are being
> machined. This is what I was replying to - centering,
> within limits, is irrelevant, but I used the wrong term
> "coaxiality." Once again, important is the
> "perpendicularity of axes and contact surfaces," and
> anything that throws this off will cause problems.
>
> In fact, there is the possibility that jim beam, too, is
> talking about this when he writes about the importance of
> centering: in a message at another list he wrote of the
> importance of cleaning the mounting surfaces of the lathe
> and of the disk.

Another factor is also how the disk is actually cut. Not only is each axis
perpendicular to each other, but the surfaces for the pads to be parallel.
A poor cutting bit, taking off too much at a time, or a crossfeed that is
too high can cause these kinds of problems.

I just went through all of this with Chrysler, as the Jeep Cherokee's from
2000-2003 are notorious for premature warping of the front rotors (TSB
issued). They (Chrysler) went through the trouble of changing the calipers
and pads to another design in accordance with the TSB recommendations, but
only cut the rotors (which I argued against), and they were warped again
within 4K miles. I gave up arguing with them and purchased and installed a
set of high performance rotors and pads.

 

karl wrote:
>>== 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.

 

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?

 

================================================== ============
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!

 

"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.

 

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.

 

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.