Why turn it down ?

[Huzo]

A standard car disc is quite thick compared to a bike, removing 1/64" off the disc is only a small fraction of the serviceable range of thickness, but a bike disc will be getting closer to the minimum allowable thickness pretty fast employing this practice.
BTW.
How is your riding going over there Timmy ?
Issues.. ?

[TimmyTheHog]

 

Thanks for taking the time to reply me :)

[yogidozer]

At one time turning rotors down was common on cars/trucks. Now the rotors are not as thick as they once were, and replacements are not that expensive, in many cases.
A thinner rotor will be more subject to warping, and the cost of turning them in the first place makes replacement a better option.

[TimmyTheHog]

A thinner rotor will be more subject to warping

Hmm...this never occurs to me until now...

Good point...

[oldlegs]

Also most car discs I think are cast and easy to turn down but bike discs are a springy material and bend away from the cutting tool.

[pyoungbl]

Also most car discs I think are cast and easy to turn down but bike discs are a springy material and bend away from the cutting tool.

Yes, indeed.  Also, many bike rotors are stainless steel and not a good candidate for turning down without deflection.  A surface grinder is best for this application.

I did this on a Ducati rotor only to discover much later that the disc was never warped at all...just not floating like it was supposed to be.

[Chuck in Indiana]

Over the years, I've never put an indicator on a pulsing rotor to find it warped. It's always been uneven deposition of pad material or stuck bobbins. That's not to say it can't happen, of course.. but..
Ferinstance.. it's not uncommon to have pulsing with aircraft brakes. Generally, aircraft brakes aren't used as hard as an automotive application.. and it's just uneven deposition. A quick trip to the bead blaster cures it.

[Huzo]

I'm starting to run out of ideas..
It has to be contaminants or runout. Unless someone throws their hands up in horror, I'd put the disc in a lathe and spin it up while holding emery cloth against it by hand.
Then bead blast to remove any trace of deposit left by the emery cloth.
Thinking about it more, the dial indicator thing is BS because it's a floater. I'm perplexed as to why the brake pulses yet there's no feeling at the lever, that's suggesting strongly that it's not runout...

[lucian]

On the Cali 14's, a known cause of front brake pulsing is caused by the brake pads wiping the rotor beyond the solid surface area on the rotor itself. So in actuality the pads wipe across the rotor spokes and create a rather sever pulse. When the rotors are new it's not an issue, as the spokes and the wipe area are at the same plane.  Unfortunately, as the rotor wears , the spoke area becomes proud and begins to drag on the pad edges. The problem is resolved by adding some washers as spacers to elevate the calipers slightly to get the pads above the rotor spokes.  Worked a treat on my 14 custom.
Ideally, rotors should be designed with the wipe area thicker than the spoke center  so this couldn't happen.