Well Tammi, rotors DO wear, even if the only friction contact was from the materials of the brake pad itself. These materials are softer than the rotor, and are made that way for several reasons, one of them being minimal wear on the rotor.

From looking at your old pads (or what is left of them), there had been alot of metal to metal contact from the backing of your pads and the rotor itself.

You see how your old pads have been "ground down" ?

The same holds true for the rotor.

An overly thin rotor can have a catastrophic failure if a heavy braking situation arises, which is almost always an emergency situation.

Unfortunately, I have seen the results of "just throwing a set of pads in " first hand. It was over 20 years ago, and my friend Brian had a CB-350 Honda who thought the metal to metal wear on his rotor was fine, and put new pads in.

He was on a bridge, an oncoming car swerved to miss debris, he slammed his brakes, the front rotor exploded and Brian was thrown from his bike into the path of the oncoming car.

Brian died on the scene.

RIP BJ

I think callipers would do ya fine. Gigital callipers can be had inexpensively & they work fine.
I would have tossed pads on the thing too. Maybe I need to rethink things a bit. What I did on a car, with a rotor with cast iron webbing between the friction/pressure bearing surfaces doesnt quite translate straight across the line. If the thing is thinner than the book recommends, the first thing I can see is it would lack heat dissipation abilities & tend to warp. A war[ed rotor can quickly lock a wheel & on the fron, total disaster..., rear? Most likely disaster, but we have drums back there, so not really the same issue. Like the man said, Be cautious here. As much as I like to save $$$ , it's hard to enjoy the savings from the emergency room, even less so from the morgue. Sorry to be so grim, but, brakes are serious bizniss. How many miles did the grinding continue? Also, when you measure the calliper, dont allow the outside edge to keep you from reading the swept area of the pads on the rotor. This may actually be a place for a micrometer. Unless you are able to shim the rotor & account for the shims in the digital calliper reading. That way, the outside edge of rotor can be managed so as to not affect the calliper reading. There are folks here who can easily explain the way to do that. I can do it, just not so sure I can explain it succinctly,
Excellent pics & gald you are posting what's going on. You may have saved me some real problems.. or someone else

Tammi, the miles do seem low but maybe not - are you in stop and go traffic a lot? - if so miles really aren't a good measure of much except tires maybe when you compare city miles to back road or hiway miles.

Might be worth considering the drilled low carbon steel rotor from ebc and the HF ceramic pads from SBS - good bit more powerful brake - for a single piston that is.

Now hang on a sec - seems unlikely the rotor is "broken" - if the groves will not hang a finger nail and the thickness is with in spec - I wouldn't replace it unless I was going to upgrade.

Rotors are not heat treated to a high hardness nor are they case hardened.  Their base material hardness, strength and toughness is what they operate from.

A rotor gets hot in normal use, easily over its lower transformation temperature (or first draw temperature, if you like)  during a "down the mountains" braking session.   Normal old medium alloy steel rotors did sometimes turn a light blue in similar conditions and still worked fine afterwards.  

Our rotors are stainless steel (noted for toughness among machinist that have to cut the stuff).  Car rotors are commonly made of nodular cast iron which is weaker and more brittle but still works OK because all disk brake rotors are squeezed with a balanced set of opposing forces that result in no deflection force on the rotor.

If Tammi has actually hurt her rotor she will feel "pulsing" from the front brake that won't go away.  She very likely just needed to clean up whatever small surface roughness that exists, which she did already with the sandpaper.

Before I threw a $143 rotor away, I'd have it turned on a double bit rotor turning center (if they can figure how to index the hole and shoulder flange correctly).  As long as the resulting trued up plate was within service thickness limits after the clean up, she'd be fine.

Oldfeller

Actually, the topic got me to thinking and I realized I didn't want to go through any of the hassels associated with any of the rotor truing mess at 5,250 miles on my original OEM brake rotor, so .....

I just now went out and changed the front pads out with the SBS ceramic pads I bough a while back (to have them on hand when the stock pads wore out unexpectedly).

What I found was that the inside pad was worn significantly more than the outside pad and I was inside the groove limit on the inside pad.  Still had some meat left to the bottom of the groove on the outside pad.  This is logical because our rotor assembly floats from one side on two rubber sheilded and greased pins -- meaning one side drags the rotor slightly some of the time while the directly hydraulic piston actuated pad likely gets sucked back by the piston return motion to be completely out of engagement when relaxed.

So, in a sense I was "on time" to change out the pads, not extremely early like I had thought.   Odds are I could have gone 2,000 more miles before actual grinding began, but why worry with it?  Pads don't cost that much.

Sanded the rotor by spinning the tire by hand while applying 320 grit cloth backed paper.  I did this until I felt I was wasting my time (you are NOT going to remove the little grooves BTW -- you are just polishing up the top and bottom surfaces of those grooves)

I used the blue permatex anti-squeal compound on the backs of the pads.  This is an alcohol based gasket sealer type compound -- it is sticky and rubbery when fully set.

To get it fully set I warmed up the pads on the eye of my wife's stove on LO heat.  I applied 3 coats of the stuff being mindful that the piston side engages on the middle circle ring that matches up to the circular piston surface and the other side engages right up against the outer ear in a rectangular fashion (two sided of course) where ear tabs come off the brake piston assembly on that side.

I heat cured the 3 coats until they were dry and rubbery to the touch.   Then I loosened the brake fluid reservoir fill plate, wrapped it in a towel to catch the leaks and pushed the piston back with a "C" clamp to create clearance for the thicker new pad assemblies.  

I sprayed piston assembly nice and clean with a can of brake cleaner then blew it off with compressed air to get everything nice and dry again.  Very lightly greased the pin and the brake pad holes, put the plates in their right places inside the spring assemblies with the anti-squeal coating matching their engagement surfaces and set the pin down inside the holes in the plates and lightly engaged the pin threads.

Everything slid on to the rotor and lined up correctly the very first time -- so of course I couldn't trust it so I slid it apart and put it back together again a couple more times until I was sure everything when where it was supposed to be and all the tabs were in their pockets, etc.  I think if you can get the pin to slide into the pad holes that actually locks everything down pretty good, so assembly to the rotor is really pretty easy and fault-free to do.

Looking at the torqued up assembly vs. the rotor showed a BIG gap between the outside pad and the rotor.  Actuating the brake lever very lightly moved the entire piston assembly on the two slider pins (and even that slight force deflected the rotor slightly but visibly).  As soon as I had the slightest feel of "bottom" I stopped actuating the brake lever.

Test ride was very gentle, I just wanted to feel the pads seat onto the rotor and make sure they retracted cleanly.  I really want the anti-squeal to fully harden before I go trying to do any heavy braking.

Looked at the rotor while it was apart.  Rotor looks like it was a piece of flat "to final size" stainless steel plate that got hit with a laser to make the final part form.  Best way to dress these plate-style puppies might be on a large surface grinder (take the entire thickness down at the same time with the best side oriented down on the magnetic plate, then flipped and ground again for good parallelism).  

However, I think you really don't need to worry very much about dressing the rotors, the wear on the rotor was very slight (a few thousandths per side).  And that small amount of wear might be decieving to measure because it looks like there is some sort of paint/powdercoat on the rest of the spoke portion of the rotor plate and that would be additive to the original metal thickness (and not present on the friction surface anyway after some use).

Now we will see if the squeal fighting tricks on the front end of the bike actually work.  I think I did them all, so we shall see if the OEM "standard squeal" is gone for good.  

Back brakes will get cleaned and the back side anti-squeal tricks done there pretty soon as my back tire is going to need changing out before too awful long.

Oldfeller

Realthing,

I used a 6" Mitutoyo digital caliper that spans over the tops of the groove tops just about the entire width of the wear zone.  I got the same answer just about everywhere when trying 5 times/places, so I think it is relatively "a good reading" for a caliper.  

I had to lay down on the ground on a blanket to get a stable enough grab though, calipers need a "steady body" to get the true minimum readings as ANY tilt in any axis increases the number that you think you are getting.

0.1750" or 4.44mm  (with all variation within -0.001")

Oldfeller

Hey, Tammi, if you can get the front end off the ground, say with a come along? & can get someone to OHHH so very lightly, squeeze the brake so you can just turn the wheel by hand, IF they can keep steady pressure & you can rotate that wheel & not feel the thing trying to stop in places or get easier in places, then you can rest assured the rotor is true. In fact, if you just apply the brake & then roll the bike, the pads will pull back a bit & you should be able to Hear the rotor scrub & lighten up, scrub & lighten up, with each revolution IF its warped.  

I suspect the rotor that exploded, causing the crash, was cracked before he grabbed it hard. From what I am seeing & hearing I really doubt Tammi has a problem. The SS rotor is tougher than the backing plate of the pads & even they arent all that gouged & galled looking. I couldnt see any deep stuff & she said it passed the fingernail test.. I think she is okay, BUT, the seriousness of the front brake requires she be extra cautious.  Tammi, the area of missing pad looks like quite a bit of metal was dragging on the rotor. From what I saw, I would think it had been squalling for a few hundred miles, at least. I would look at the depth of the wear, not just the ridges vz. grooves distance, but, the very edge of the rotor doesnt get the pads on it. Correct? so, IF the rotor is worn down from the scraping, there should be a ridge at the edge. The pads were worn to the metal, one inside on the rotor, the other, toward the outside, so, the depth of the wear at the edge of the rotor & then towards the axle would each need to be looked at.    IF I am reading those pads right, the wear on the rotor would look like this.. /  / in a very exagerated way. I dont see that as a problem, just as a way to help Tammi "see" what it is she is looking at. Anyone disagree with this? Please, speak right up. I dont want to worry or misguide her needlessly.

Good Luck, Tammi, I THINK this is gonna be allright, but, I can't see it & would feel real real bad if I gave you wrong info & you got hurt, so I am leaning to caution.