New rotors are milled at the factory, leaving a non-directional finish.
"Turned" rotors on a brake lathe end up with the equivalent of a very fine
"thread" which should removed with an abrasive disc whicle the rotor is
still chucked up and turning. Failure to do this can result in a clicking
sound when the brakes are applied or released.
Rex Burkheimer
J-CON Coordinator, WM Automotive Whse Fort Worth TX
Texas Region SCCA FC #19 SRX7 #39
rex@txol.net rex@ceoexpress.com
"There is pleasure sure in being mad which none but madmen know." John
Dryden
----- Original Message -----
From: Peter J. Thomas <pjthomas@ntplx.net>
Cc: <shop-talk@autox.team.net>
Sent: Tuesday, February 22, 2000 7:55 PM
Subject: Re: To cut or not to cut
>
> "B. Vibert" wrote:
>
> > > This is quite true, but has more to do with hard spots, rather than
high
> > > spots. The cutting tool is more likely to deflect at points where the
> > > rotor has work-hardened from heat (these areas are sometimes
> > > 0.010-0.015" deep and must be undercut, which requires more tool
> > > pressure). And, quite so, tool pressure on both sides of the rotor
> > > ensures that the cut is true on both sides in the direction of
rotation.
> > >
> >
> > I've tried turning rotors in a lathe, it's rarely worth the time and
trouble as
> > the results are usually not very good for the reasons Doug mentioned
above. If
> > you cut one side and then rechuck it is quite difficult to get it
parallel with
> > the side you just faced. I've used very accurate dial indicators when
> > rechucking, even tried facing both sides without rechucking, and still
had
> > pulsations.
> > I think the problem is not so much with warpage as with minutely varying
> > thickness in the rotor, probably from the harder spots in the rotors.
> > While a warped rotor will shudder somewhat, a varying thickness one is
very,
> > very, much worse. This is why the real brake lathes face both sides at
once.
> > Usually it's not worth the trouble to turn them as new ones are not
really that
> > expensive.
>
> The replacement rotor I bought was not turned, it was milled. Not being a
> machinist, common sense (usually wrong) suggests that this would avoid the
high
> spots from hardening. However, the high spots would appear after the pads
set in
> because brake pads themselves act as a tool on a lathe.
>
> > I have no experience with drum brakes.
> >
> >
> > 1997 Shetland Sheepdog
>
> Peter Thomas
>
> 1966 Triumph TR4A IRS
> 1996 Ford Windstar GL
> 1991 Shetland Sheepdog
>
>
>
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