Dialing up a brake disc on a lathe, help

[dobbslc]

Thanks for the replies. I've now got a new EBC disc!
£53 but I do get a trade discount.
It's even made in England!!!
To be honest that's what swayed me, rather than buy some Chinese job that goes banana shaped on the first proper stamp of the pedel.

 

[Wedg1e]

I'm trying to skim a small (200mm from the rear of a motorcycle) brake disc on my lathe, what's the best way to dial it in on a 3 jaw chuck to run true?
I'm not sure it's even possible to take a small skim off it but worth a try before splashing out £45 on a new one!
I have a dial gauge etc.
Thanks

To return to the original post, I've done it by opening the jaws so they grip the centre bore of the hub. You may find a small amount of eccentricity (radial run-out) but for the purposes of a skim it's irrelevant. You could improve it by packing one jaw with a piece of paper (works for gripping external surfaces too if your chuck's a bit worn).
Brake discs are usually machined to quite close tolerances so if you use a clean face of the hub against chuck or faceplate then the friction surfaces will (or should) all be trued square.
As an aside I've heard of people using old brake discs as 'emergency' lathe faceplates... simply drill or slot to suit the job you need to do and scrap the disc afterwards.

 

[Shox Dr]

As an aside I've heard of people using old brake discs as 'emergency' lathe faceplates... simply drill or slot to suit the job you need to do and scrap the disc afterwards.

Clutch flywheels are also very handy

 

[dobbslc]

Good ideas, the problem with mine was it was "damaged" during a drunken garage raid one summer's night......
My mate asked if he could do a burn out, I said yes, he lit it up and BANG!
Bits of metal everywhere.
I'd forgotten the small padlock I'd fitted through the rear disc for security purposes!!!
So I think the disc was probably bent from the mounts outwards rather than just warped as I couldn't get it sitting true on the lathe from the inside diameter and it got worse the further out I measured.

 

[Shox Dr]

Good ideas, the problem with mine was it was "damaged" during a drunken garage raid one summer's night......
My mate asked if he could do a burn out, I said yes, he lit it up and BANG!
Bits of metal everywhere.
I'd forgotten the small padlock I'd fitted through the rear disc for security purposes!!!
So I think the disc was probably bent from the mounts outwards rather than just warped as I couldn't get it sitting true on the lathe from the inside diameter and it got worse the further out I measured.

In that case you would have never got it back flat.

 

[PhillipM]

Thanks for the replies. I've now got a new EBC disc!
£53 but I do get a trade discount.
It's even made in England!!!
To be honest that's what swayed me, rather than buy some Chinese job that goes banana shaped on the first proper stamp of the pedel.

Yep, now you have some english stuff that's goes banana shaped on the first proper stamp of the pedal instead