[Kreylyn]

I'm pretty sure most bike rotors are worked from sheets using processes like milling from flat stock... Lot of mill marks on my rotors anyways.

I'm curious the hardness of the material to start with.... anyone have a rockwell tester? Would also be interested in knowing what type of steel is used.

Krey

[rexazz2]

I'm pretty sure most bike rotors are worked from sheets using processes like milling from flat stock... Lot of mill marks on my rotors anyways.

I'm curious the hardness of the material to start with.... anyone have a rockwell tester? Would also be interested in knowing what type of steel is used.

Krey

could be cast then milled down to true
since its not vented who's to know
High school I went to had a hardness tester but that was a lot of years ago

[paul.miner]

Okay, so I took an oxy-acetylene torch to the rotor, and heated it up enough to get the same coning warp to come back (somewhere over 500, the limit of my thermometer). I then put it back on the arbor press, pressed it flat, and waited for it to cool. After it cooled, I pressed it a couple more times to correct it (it was a little off).

Do you think this is enough? I hate to just toss a rotor because it coned (searching around rotor mfr pages, that seems to be what this kind of warp is called). I like to think that these sorts of problems are still repairable by mere mortals.

On a side note, it seems that part of the reason newer disc rotors often have an inner mounting ring connected to the outer braking surface ring connected by relatively small webs of metal is to prevent coning; this design allows the outer braking ring to expand without being constrained as much by the inner mounting ring.

[RossW]

You don't want to replace a key safety item because it's damaged? Seriously, the money for a new rotor is small beans compared to a wrecked bike and a trip to the hospital. Why risk it?

[paul.miner]

You don't want to replace a key safety item because it's damaged? Seriously, the money for a new rotor is small beans compared to a wrecked bike and a trip to the hospital. Why risk it?

I already bought a replacement, so the money isn't the issue.

It's a plate of metal shaped like a disc. I just have a hard time accepting that it's ruined beyond repair because it overheated once. This seems like something that should be repairable, so I'm trying to figure out how.

[H-2 CHARLIE]

most shops wont even turn rotors they are throw-away parts ...brakes are something you dont want messing up or cracking while your driving at high speeds ... toss it and dont look back

[scottynoface]

most shops wont even turn rotors they are throw-away parts ...brakes are something you dont want messing up or cracking while your driving at high speeds ... toss it and dont look back

+1

[paul.miner]

Well, I'll be replacing it in a few days when the eBay rotor arrives. I just rode around on the original rotor, and it seems to be doing okay. The rotor temperature after the ride was higher for the rear rotor (150s for the rear vs 120s for the front), but it still looks to be nearly centered.

Given what's been posted in this thread, I think I'm safe as long as I don't get the rotor excessively hot. I'm going to keep an eye on it, make sure the temps stay reasonable, but I will ride it at least until the replacement gets here.

[rexazz2]

in your picture you are supporting it to be pressed with nuts , bet if you use a micrometer on the nuts alone they will vary in size
how true will it be ??? good question huh !!!
figure out how fast it is spinning at highway speed or higher, do you want to risk it breaking up that close to your butt?
not to say it can't be done, but does the money and risks warrant it ???

[The CyberPoet]

usually car rotors are made from cast iron , hard to the point of being brittle

Modern motorcycle rotors designed to work with sintered or semi-sintered pads, like those on the Kats, are typically made of steel (SS is common). The exact blend I'm not sure of, but it is a steel. The braking interaction is actually designed to occur between a layer of transferred friction material onto the rotors (coming from the pads) and the pads' friction materials itself; this is part of why our calipers don't retract the pads away from the rotors when you're off the brakes (letting them skim the rotor instead without any serious pressure on them).
This interaction system is designed to prevent any significant rotor wear over time, and the only time steel rotors normally wear on bikes is when either the pads aren't replaced in a timely manner (backing plate or rivets rubbing into the rotors), or external debris that's harder than steel (quartz-based sands, certain clays) get between the rotor and pads and act as a scouring agent (typical result is highly grooved rotors).

Cast iron brakes on bikes are designed to work with organic pads, both of which are designed operate at a much cooler operating temp range than sintered & semi-sintered, and the organic pads are specifically designed to be mated to calipers that retract the pads away from the rotors when not actively braking. It's not nearly as good a design for our purposes as urban bikers in all-weather climates including rain (although theoretically better for very long-haul touring where the brakes are rarely used).

On a side note, it seems that part of the reason newer disc rotors often have an inner mounting ring connected to the outer braking surface ring connected by relatively small webs of metal is to prevent coning; this design allows the outer braking ring to expand without being constrained as much by the inner mounting ring.

Most brake rotors sit on a series of aluminum/titanium/etc. hubs that connect them to the base which mounts to the wheel. These hubs serve a couple different purposes:
1. They permit the rotor surface to move inward/outward without mis-alignment issues (at least if the hubs aren't worn; if you can push one side and not have the other side move the same distance, it's time to replace it). This makes exact placement in reference to the caliper not hyper-critical, especially on dual-sided calipers.
2. They act as a partial heat-barrier to keep the rotor's heat from traveling down to the base of the mounting and cooking the bearing grease in extreme use or high-temp environments. They also help allow the braking surface of the rotor to come up to operating temp quicker in cooler weather (by reducing the total heat-sink size).


Cheers
=-= The CyberPoet

[paul.miner]

in your picture you are supporting it to be pressed with nuts , bet if you use a micrometer on the nuts alone they will vary in size
how true will it be ??? good question huh !!!

I'm positive that the nuts did vary in size, but I was not overly concerned.

figure out how fast it is spinning at highway speed or higher, do you want to risk it breaking up that close to your butt?
not to say it can't be done, but does the money and risks warrant it ???

Here's the thing: I've heard a lot of talk about this possibly happening under extreme heat, but so long as it doesn't get that way, I don't see it happening. Even under the extreme heat that caused the problem in the first place, it just coned the rotor.

[rexazz2]

So far!!

[Kreylyn]

I wouldn't be overly worried about it "breaking"...

The temperatures it's heated up to (500-600) is the tempering heat range for steal (process that allows for stesses to relieve themselves and makes the steel LESS brittle). If nothing else, they are a little softer now and less likely to break, more likely to bend or warp/cone.

As you mentioned, appling the heat coned them again, which is what I thought would happen metal memory wise. Your probably right in that if you baby them, and keep them cool with light use, it probably won't be an issue until replaced.

I would replace them though, because I wouldn't want to have to keep in mind I needed to be easy on them. The issue at this point is them coning on you out on a ride, and causing further issues from the heat build up if they do and your don't notice.

Krey

[DumbLuck]

hey paul, how about setting me up as the benificiary for your life insurance?

[paul.miner]

hey paul, how about setting me up as the benificiary for your life insurance?

Some would say the same to you for even riding a motorcycle. As with many things, it's a calculated risk. I figure the risk is low to non-existent. The payoff is that I get to ride all week!