Brake Disc Skimming

[hotponyshoes]

A mate of mine has a tool that bolts to the caliper mounting points and faces both sides of the disc after it is fitted to the hub so that it is 100% inline with the caliper.

I have also seen him bolt discs to a rotary table and face them on a mill to reduce the thickness so he can fit bigger pads.
He finishes the surface with a flex-hone type tool to save on having to bed the pads in.

He does this on new discs but he also faces his brand new pads.
He is actually racing though. I just mess about on the track.

 

[mcostello]

Over here the last set I installed the disks were at the minimum thickness while still in the box. Could not be turned down before being used.

 

[chris y]

I have a decent size lathe and have skimmed one set of discs.

Its not easy to get the parallelism you need on a lathe.

Certainly if you just stick it in the chuck, skim it, turn it round and repeat you will be nowhere near.

The advice I was given from old school machinists when I was a boy was to turn a boss to hold the disc, then skim the boss after mounting it in the chuck before each use to guarantee that its true.

I cant remember now but the discs I did were parallel to a few hundredths of a mm but reading online it wasn't good enough.

I still have them fitted, and did a track day so some very hard braking, I guess they h

It looks like the end of this post went missing when it was moved from the other thread (where I shouldn't have put it as it was a welding discs question).

Edit to add - I guess they have done about 15k miles now, and in some conditions they vibrate under braking.

I understand that if you start with them out of parallel they become worse without use as the pads grip hard on some parts of the disc and loosely on others, so to prevent them becoming out of parallel they have to be very parallel in the first place.

From my experience I wouldn't do it again unless new discs were unobtainable or crazy price, and it isn't as easy as it sounds to do a good enough job one side at a time on a lathe.

 

[scott0031]

The last place I worked had a machine for facing discs & drums
They were ground after machining
This is only viable on specialist vehicles
Discs for most popular cars are very cheap
Basic Vauxhall Corsa discs less than a tenner each
Even big Audis etc are only £ 30 ish trade
I have no idea how they make them so cheap

Volume, prices tumble with volume. It's bread and butter work all day long, every day.