Most brake lathes indeed DO single-point turn rotors, and drums too, for
that matter. The swirl patterns are produced by an orbital sander-style
apparatus, or in some cases by an actual hand-held orbital sander. These
are intended to produce a non-directional pattern on the surface of the
rotor to aid in quick and smooth bedding of the pads, without any influence
from any potential radial runout induced by the (spiral) turning process.
If your local automotive machine shop doesn't do the swirl finish and you
want it, you can run a DA sander with aluminum oxide paper on it over the
rotor as you turn it smoothly by hand while installed on the spindle. Even
better if they'd do it on their machine while it turned slowly. If you need
to do it on the car, be REALLY careful to get all the grit off when you're
done - it's very abrasive and any in your bearings would be an invitation to
early wheel bearing failure. If you do it on the car, it would be best to
use old bearings and an old seal while sanding, then disassemble, clean
everything, and install new or thoroughly cleaned and repacked bearings and
new seals.
- Karl Vacek
'66 TR4A - IRS
'64 Amphicar
'16 Ford T Touring
'46 Piper J-3 Cub
Michael Marr wrote...
>The comments on the pattern left on the brake rotor started me thinking.
>The "swirling" pattern, if its what I am thinking it is, is typical of one
>left by a grinding wheel when the side of the wheel is doing the cutting,
>rather than the periphery of the wheel. The mark left by a single point
>cutting tool is actually a spiral, the pitch of which is detrmined by the
>tools feed rate acroos the face of the rotor. After all these years of
>having rotors turned (which, by definition, implies that a single point
>cutting tool is used), I am wondering if, in fact, some so called "turned"
>rotors are actually ground? Can anyone confirm this?
>As an added kicker, a worn single point tool bit will "chatter", which will
>leave a pattern on the face of the rotor that could be construed as a
>"swirl". Maybe we are also seeing this?
Wayne Brazinski wrote...
>Coincidentally(?), the marks left on the newly turned rotors are in a swirl
>pattern. Maybe there's something to your emery cloth idea.
|