MOT failed on scored discs

I remember it was commonplace to skim discs a few years ago: given they cost so little these days, for most cars I doubt it's worth it. Even OEM disks are often below £25.

The one I remember was that my Capri with badly scored disks used to eat pads quickly, new disks & the pads outlasted the car.

Reminded by this topic I've just had a good look at my front disks after getting back from the shops. 15k miles after skimming them and fitting new pads there's only a minimal wear lip and the rubbing surfaces are smooth as a baby's bumpty. Not a groove in sight. Without a doubt I've made them last for two sets of pads instead of just one by skimming them instead of chucking them at 34k miles and when you have your own lathe and carbide tooling I think that's a fairly cost effective use of time.

Perhaps they do sell second hand ones. However ...

1) I bought new ones last year. They are currently =8079.45 from myparts, or =A380 from Brodies, though mine came from Andre Pol. 2) My old ones had worn to about 2/3 of the new thickness 3) Fitting them is dead easy ... as long as the engine and transmission are out of the car. Bit harder otherwise, but not impossible.

Ian

Ian

Ian gurgled happily, sounding much like they were saying:

IIRC it's the '50s style - the ones for the clockwork calipers.

I've tried skimming discs on a lathe in the past and have never had much success, and that is with using a carbide tool bit. The problem appears to be caused by harder chilled areas (spots) of the disc which although hardly measurable, result in those areas being slightly raised. Which gives slightly juddery braking. This as using an old Colchester Master, which I've an idea isn't really rigid enough to do the job. Presumably the lathe you use is something a bit more solid, that is not so easily affected by slight variations in the hardness of a disc. Mike.

I would have expected them to be refinished with some sort of grinder rather than straight cutting. American tyre and brake places use a portable machine to refinsh them on the car, that would only seem possible using a grinding mechanism of some sort.

AFAIK there is a dedicated machine for the job that grinds both sides of a disc simultaneously, but I don't know of any Co in the UK that has one. Mike.

Japanese car tuning firms seem to have a liking for them.

Yet our US cousins refer to it as 'turning the rotors'. Wonder just why it is so popular there but not here?

Because it took them far longer to actually make discs & hubs with parallel faces? Plus they do tend to drive heavier cars.

It certainly took them much longer to 'discover' discs for the average car.

My machine is a very old Student so not much different to yours. Using the right carbide inserts is the key. Very sharp, uncoated, non ferrous finishing inserts which should be silver in colour. Inserts for steel will do more tearing than cutting. However I run into hard carbide spots mainly on flywheels. I don't recall much of a problem with them on disks. A coarse oilstone finishes them off quickly enough if you do end up with any proud spots.

It's a cultural thing. They have the customer volumes and demand over there to make it worthwhile getting properly tooled up which means quick machining times and low labour cost compared to the price of new disks. We've never really got into it so no one has the right equipment and trying to do it on a basic lathe means long set up times and high cost. For me it's a zero cost exercise because I have my own lathe but if I were to charge for it at reasonable rates it probably wouldn't make sense. Over there you might pay $20 to $30 for a pair of disks to be skimmed but the equivalent £10 to £15 over here wouldn't buy you the time to print out the invoice for the customer. If you were doing dozens of them day in and day out it might be different.

Boubtless, as you say, for those of us with the tooling, but probably uneconomical for those (like me) that would have to pay someone.