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Originally posted by ed
What Gary said - we did it at uni and it was a pretty big job in terms of hours spent. They were a 2 axis mill job and then ground flat. The material used was some kind of cast iron plate (alloy I assume). Don't have many details on it than that.

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I was involved in making a couple thousand of the oversize rotors per year for several years. Good work until offshoring killed the profit in it.

We used 410 SS, not because it was necessarily the best material for the application, but because people seem to want something that stays shiny. Analysis of a stock Japanese rotor showed the material to be closest to 410.

Our rotors were laser cut from 11 ga sheet. Vacuum heat treated, jig tempered to Rc36-38, and blanchard ground to about .100 final thickness.

The rotors are thin to minimize rotational inertia as well as overall weight. IMO, ductile iron would likely be the best common material, but at that sort of thickness I doubt it would be reliable. We tested some non heat treated 410 rotors, and they didn't hold up well at all in cow pasture type testing. I was working with a 7X national enduro champion and AMA hall of famer on the parts, so the tester was pretty high on the legitimate testing scale. We used a lot of different patterns of slots and scalloped OD profiles to try to maximize the scraping effect to keep mud cleared from the pads. Some worked lots better than others, but I wasn't involved in that part of the work so I don't have any knowledge of what did or didn't work best.

If I was going to experiment with different steels, I'd start with abrasion resistant sheet and have the parts water jetted. That would bypass the hardening and tempering ops, which are a pain on pieces that large and thin. That would allow you to cut the part, grind for thickness and flatness, and do whatever necessary countersinking or spotfacing at the attachment points as the final operation. Probably try some AR360 first, and then something in the 300 range.

Considering the thickness of the rotors pretty much limits one to using steel rather than any other material, my gut instinct would be to concentrate on various pad materials as there's likely more difference there than what you'd find from one steel to another. All things considered, even the best combination is going to be a somewhat poor compromise as compared to a good brake design.
motion guru and Joe Miranda like this.

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