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Turning rotors on a shop lathe

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  #1  
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Proctologically Violated©®
 
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Default Turning rotors on a shop lathe - 04-12-2009 , 12:07 PM






Awl --

First, how "rough is rough" before you have to turn down a rotor?
In the two rotors I just took off, one face was quite smooth, two faces were
smooth but a little "ridgy" or ripply, and one was obviously scored and
gouged. Is ridgy/ripply OK?

Next, the rotors fit quite well on a 13" lathe with a 6" chuck, and the Q
is, how much flatness is required, ito of the rotating plane?
If I put an indicator on this, what swing of the needle is tolerable,
*before* turning?

tia.

--

Mr. PV'd

Mae West (yer fav Congressman) to the Gangster (yer fav Lobbyist):
Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just
glad to see me??







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  #2  
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Ashton Crusher
 
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Default Re: Turning rotors on a shop lathe - 04-12-2009 , 01:01 PM






On Sun, 12 Apr 2009 13:07:41 -0400, "Proctologically Violated©®"
<UNfitcat (AT) UNoptonline (DOT) net> wrote:

Quote:
Awl --

First, how "rough is rough" before you have to turn down a rotor?
In the two rotors I just took off, one face was quite smooth, two faces were
smooth but a little "ridgy" or ripply, and one was obviously scored and
gouged. Is ridgy/ripply OK?

Next, the rotors fit quite well on a 13" lathe with a 6" chuck, and the Q
is, how much flatness is required, ito of the rotating plane?
If I put an indicator on this, what swing of the needle is tolerable,
*before* turning?

tia.
I don't recall the numbers but the spec is VERY tight. I think it's
in the ten-thousandths. That's why the only way to get some rotors
adequately "flat/parallel/zero runout" is to use an on the car lathe.


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  #3  
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Pete C.
 
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Default Re: Turning rotors on a shop lathe - 04-12-2009 , 02:33 PM




Ashton Crusher wrote:
Quote:
On Sun, 12 Apr 2009 13:07:41 -0400, "Proctologically Violated©®"
UNfitcat (AT) UNoptonline (DOT) net> wrote:

Awl --

First, how "rough is rough" before you have to turn down a rotor?
In the two rotors I just took off, one face was quite smooth, two faces were
smooth but a little "ridgy" or ripply, and one was obviously scored and
gouged. Is ridgy/ripply OK?

Next, the rotors fit quite well on a 13" lathe with a 6" chuck, and the Q
is, how much flatness is required, ito of the rotating plane?
If I put an indicator on this, what swing of the needle is tolerable,
*before* turning?

tia.

I don't recall the numbers but the spec is VERY tight. I think it's
in the ten-thousandths. That's why the only way to get some rotors
adequately "flat/parallel/zero runout" is to use an on the car lathe.
Brake lathes use a double bit setup to ensure absolutely consistent
thickness. Any thickness variations as you would likely get with cutting
the sides separately (unless you indicate them very carefully) will
produce tremendous pedal pulsation.


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  #4  
Old   
Paul Hovnanian P.E.
 
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Default Re: Turning rotors on a shop lathe - 04-17-2009 , 07:33 PM



"Pete C." wrote:
Quote:
Ashton Crusher wrote:

On Sun, 12 Apr 2009 13:07:41 -0400, "Proctologically Violated©®"
UNfitcat (AT) UNoptonline (DOT) net> wrote:

Awl --

First, how "rough is rough" before you have to turn down a rotor?
In the two rotors I just took off, one face was quite smooth, two faces were
smooth but a little "ridgy" or ripply, and one was obviously scored and
gouged. Is ridgy/ripply OK?

Next, the rotors fit quite well on a 13" lathe with a 6" chuck, and the Q
is, how much flatness is required, ito of the rotating plane?
If I put an indicator on this, what swing of the needle is tolerable,
*before* turning?

tia.

I don't recall the numbers but the spec is VERY tight. I think it's
in the ten-thousandths. That's why the only way to get some rotors
adequately "flat/parallel/zero runout" is to use an on the car lathe.

Brake lathes use a double bit setup to ensure absolutely consistent
thickness. Any thickness variations as you would likely get with cutting
the sides separately (unless you indicate them very carefully) will
produce tremendous pedal pulsation.
I'd also think that getting the rotor true to the axle flange would be
important. It would be better to make a jig that resembles that flange
which can be mounted and trued in the lathe chuck. Once that is true,
mount the rotor to that and then tuning it will bring its faces and the
axle interface parallel.

--
Paul Hovnanian mailto:Paul (AT) Hovnanian (DOT) com
------------------------------------------------------------------
The ark was skippered by amateurs, the Titanic was skippered by
professionals.


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  #5  
Old   
Tegger
 
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Default Re: Turning rotors on a shop lathe - 04-17-2009 , 07:41 PM



"Paul Hovnanian P.E." <paul (AT) hovnanian (DOT) com> wrote in
news:49E91FC6.838A6201 (AT) hovnanian (DOT) com:

Quote:
"Pete C." wrote:

Ashton Crusher wrote:

On Sun, 12 Apr 2009 13:07:41 -0400, "Proctologically Violated©®"
UNfitcat (AT) UNoptonline (DOT) net> wrote:

Awl --

First, how "rough is rough" before you have to turn down a rotor?
In the two rotors I just took off, one face was quite smooth, two
faces were smooth but a little "ridgy" or ripply, and one was
obviously scored and gouged. Is ridgy/ripply OK?

Next, the rotors fit quite well on a 13" lathe with a 6" chuck,
and the Q is, how much flatness is required, ito of the rotating
plane? If I put an indicator on this, what swing of the needle is
tolerable, *before* turning?

tia.

I don't recall the numbers but the spec is VERY tight. I think
it's in the ten-thousandths. That's why the only way to get some
rotors adequately "flat/parallel/zero runout" is to use an on the
car lathe.

Brake lathes use a double bit setup to ensure absolutely consistent
thickness. Any thickness variations as you would likely get with
cutting the sides separately (unless you indicate them very
carefully) will produce tremendous pedal pulsation.

I'd also think that getting the rotor true to the axle flange would be
important. It would be better to make a jig that resembles that flange
which can be mounted and trued in the lathe chuck. Once that is true,
mount the rotor to that and then tuning it will bring its faces and
the axle interface parallel.


The very best explanation of brake pedal pulsation I have ever seen;
includes precise instructions on rotor machining:
<http://www.babcox.com/editorial/bf/bf100326.htm>

Note that SURFACE FINISH is as important as TRUENESS. Chain stores and
clueless garages (dealer and independent) tend to forget that, keeping in
service lathe bits that gall and tear more than machine.

--
Tegger



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  #6  
Old   
Paul Hovnanian P.E.
 
Posts: n/a

Default Re: Turning rotors on a shop lathe - 04-17-2009 , 10:01 PM



Tegger wrote:
Quote:
"Paul Hovnanian P.E." <paul (AT) hovnanian (DOT) com> wrote in
news:49E91FC6.838A6201 (AT) hovnanian (DOT) com:

"Pete C." wrote:

Ashton Crusher wrote:

On Sun, 12 Apr 2009 13:07:41 -0400, "Proctologically Violated©®"
UNfitcat (AT) UNoptonline (DOT) net> wrote:

Awl --

First, how "rough is rough" before you have to turn down a rotor?
In the two rotors I just took off, one face was quite smooth, two
faces were smooth but a little "ridgy" or ripply, and one was
obviously scored and gouged. Is ridgy/ripply OK?

Next, the rotors fit quite well on a 13" lathe with a 6" chuck,
and the Q is, how much flatness is required, ito of the rotating
plane? If I put an indicator on this, what swing of the needle is
tolerable, *before* turning?

tia.

I don't recall the numbers but the spec is VERY tight. I think
it's in the ten-thousandths. That's why the only way to get some
rotors adequately "flat/parallel/zero runout" is to use an on the
car lathe.

Brake lathes use a double bit setup to ensure absolutely consistent
thickness. Any thickness variations as you would likely get with
cutting the sides separately (unless you indicate them very
carefully) will produce tremendous pedal pulsation.

I'd also think that getting the rotor true to the axle flange would be
important. It would be better to make a jig that resembles that flange
which can be mounted and trued in the lathe chuck. Once that is true,
mount the rotor to that and then tuning it will bring its faces and
the axle interface parallel.


The very best explanation of brake pedal pulsation I have ever seen;
includes precise instructions on rotor machining:
http://www.babcox.com/editorial/bf/bf100326.htm

Note that SURFACE FINISH is as important as TRUENESS. Chain stores and
clueless garages (dealer and independent) tend to forget that, keeping in
service lathe bits that gall and tear more than machine.
Thanks. That's a good explanation of brake problems and repair
procedures. However, I think this is written up assuming that the shop
has the requisite adapters for turning rotors on a bench lathe. Based on
the OP's post, I think he is going to try this on a shop (general
purpose machinists) lathe. Particularly the bit about the 'chuck'.

--
Paul Hovnanian mailto:Paul (AT) Hovnanian (DOT) com
------------------------------------------------------------------
2 + 2 = 5 for extremely large values of 2.


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  #7  
Old   
Tegger
 
Posts: n/a

Default Re: Turning rotors on a shop lathe - 04-18-2009 , 07:54 AM



"Paul Hovnanian P.E." <paul (AT) hovnanian (DOT) com> wrote in
news:49E94288.FEFE15BC (AT) hovnanian (DOT) com:

Quote:
Tegger wrote:



The very best explanation of brake pedal pulsation I have ever seen;
includes precise instructions on rotor machining:
http://www.babcox.com/editorial/bf/bf100326.htm

Note that SURFACE FINISH is as important as TRUENESS. Chain stores
and clueless garages (dealer and independent) tend to forget that,
keeping in service lathe bits that gall and tear more than machine.

Thanks. That's a good explanation of brake problems and repair
procedures. However, I think this is written up assuming that the shop
has the requisite adapters for turning rotors on a bench lathe. Based
on the OP's post, I think he is going to try this on a shop (general
purpose machinists) lathe. Particularly the bit about the 'chuck'.


Well, the basic concepts should still be applicable even if the exact
methods may differ, no?


--
Tegger



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  #8  
Old   
Pete C.
 
Posts: n/a

Default Re: Turning rotors on a shop lathe - 04-18-2009 , 05:41 PM




Tegger wrote:
Quote:
"Paul Hovnanian P.E." <paul (AT) hovnanian (DOT) com> wrote in
news:49E94288.FEFE15BC (AT) hovnanian (DOT) com:

Tegger wrote:



The very best explanation of brake pedal pulsation I have ever seen;
includes precise instructions on rotor machining:
http://www.babcox.com/editorial/bf/bf100326.htm

Note that SURFACE FINISH is as important as TRUENESS. Chain stores
and clueless garages (dealer and independent) tend to forget that,
keeping in service lathe bits that gall and tear more than machine.

Thanks. That's a good explanation of brake problems and repair
procedures. However, I think this is written up assuming that the shop
has the requisite adapters for turning rotors on a bench lathe. Based
on the OP's post, I think he is going to try this on a shop (general
purpose machinists) lathe. Particularly the bit about the 'chuck'.


Well, the basic concepts should still be applicable even if the exact
methods may differ, no?
Certainly. A dedicated brake lathe has special features to make the task
easier, but a general purpose lathe can certainly do the job if you take
the time with the dial indicator to ensure everything is running true
before cutting.


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  #9  
Old   
HLS
 
Posts: n/a

Default Re: Turning rotors on a shop lathe - 04-19-2009 , 05:56 PM




"Proctologically Violated©®" <UNfitcat (AT) UNoptonline (DOT) net> wrote

Quote:
Awl --

First, how "rough is rough" before you have to turn down a rotor?
In the two rotors I just took off, one face was quite smooth, two faces
were smooth but a little "ridgy" or ripply, and one was obviously scored
and gouged. Is ridgy/ripply OK?

Next, the rotors fit quite well on a 13" lathe with a 6" chuck, and the Q
is, how much flatness is required, ito of the rotating plane?
If I put an indicator on this, what swing of the needle is tolerable,
*before* turning?

tia.

--

Mr. PV'd

Mae West (yer fav Congressman) to the Gangster (yer fav Lobbyist):
Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just
glad to see me??






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  #10  
Old   
HLS
 
Posts: n/a

Default Re: Turning rotors on a shop lathe - 04-19-2009 , 06:24 PM






Sorry.. I had intended to respond to this but thought better of it.
You CAN set up a shop lathe to cut rotors.. Shop lathes, good ones,
can do a lot.

It is a lot easier with at drum/rotor lathe.

Specifications of the cut can be found on the web.

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