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Best Method of machining a Brake rotor to a smaller diameter?

Best Method of machining a Brake rotor to a smaller diameter?

Hello All,

I am in the process of converting my 1978 Honda CB750K Motorcycle to dual front discs. I am using 1977 CB750F2 forks and calipers. I have jumped the first hurdle and determined how much I need to move the K rotors out to match the plane of the F's, but now I face a diameter dilemma.The K rotors are 295mm in dia., while the F ones are 275mm. I am trying to decide between fabricating a relocation bracket for the calipers, or trimming the rotors down. If I cut the rotors down, would a lathe be the best? or a mill? All I know about the metal of the rotors is that it is stainless steel, I do not know the grade. Thickness is 6mm.

Thanks for any info!


RE: Best Method of machining a Brake rotor to a smaller diameter?


If I were doing this, I would use a lathe.  At 6mm thickness, you may want to have some sort of backup plate to stiffen it up a little bit, depending on how you chuck it up.  Be sure to check runout in both directions, otherwise you won't be happy with the result.

Happy Turning,


RE: Best Method of machining a Brake rotor to a smaller diameter?

As Fegenbush mentioned, you will want a backup plate on either side, and preferably bolted through if there are existing holes in your disc.  Otherwise it will howl like a banshee.  You could also have it waterjet cut.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

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