Disc Rotor Machining

[gman]

I am about to replace disc brake pads and bleed the system (hayes), but is there any maintenance required for the discs?

With cars the discs are machined to provide a smooth even surface for the pads to act against. How badly worn do bike discs have to be before they are replaced?

Thanks.

 

[A-line4lyf]

Really if the rotor feels thin of if they feel scored (out of shape) and how much dirt and pebbles get stuck in the callpier, you should replace them. Not sure but i have never heard of anyone who has machined their rotors (their too thin).

Depending on what pads you have and how hard you brake i recommend you should replace your rotors every second time you replace your pads.

A straight surface on the rotor and a straight surface on the pads = 100% braking power and contact!

Getting soft pads will cause less wear to the rotor therefore, you dont have to replace the rotors as often.

 

[ruffin1]

i dont really know much about this topic
but wouldnt the pads wear in and sort of mould to the disk.
obviously a new rotor would be better.

also how would you machine a rotor?
i understand you could use a lathe for a car one but with the holes in it a lathe wouldnt do the job.

 

[Dan.]

I am about to replace disc brake pads and bleed the system (hayes), but is there any maintenance required for the discs?

With cars the discs are machined to provide a smooth even surface for the pads to act against. How badly worn do bike discs have to be before they are replaced?

Thanks.

Are they worn enough that there is a significant difference between the surface of where the pads contact and the rest of the rotor. If there isnt then you dont need to do anything.
cheers
dan

 

[escott12]

If your really concerned get a photo of the rotor on an angle, so as to try show what ever grooves may have developed. IF the photo works then post it. This is just speculation, but I would think that the pressure exerted from a cars breaking system would far outway that of a bikes system. The grooves that a car rotor can experience may be due to these forces. But hey, if your rotors are worn that bad then there's the proof.

 

[Mo]

Depending on what pads you have and how hard you brake i recommend you should replace your rotors every second time you replace your pads.

WTF, that's gotta be something so stupid that i can't understand this.

please explain this in more detail, i wanna see this.

 

[Jon]

Realistically it depends on how you ride and how tight you are.If you dh and need max brakes then be concerned if you can see groves or get soft pads. If you dont need max stopping power and if they work then dont get caught up in the detail ie cant see the forest for the trees.
cheers jon

 

[2fst4u]

also how would you machine a rotor?
i understand you could use a lathe for a car one but with the holes in it a lathe wouldnt do the job.

you would have to use a mill with a large siezed bit. but milling a disc is unrealalistic due to the following
1. lets say a disc rotor is two mm thick. if you sat the disc on a perfectly flat surface and measured the amount the disc was warped (lets say it was point 25mm out) you would end up having to take half a mm off the thickness of the disc (a whole damned quater) deaming it unoperable anyway.

2. even with the biggest industrial (of course bigger ones can be made) size available for mills (wich as far as i know is about 200mm) the surface area of the mill bit would create enough heat through friction that it would end up warping it as soo as you stoped milling.

with that in mind its probably easier to use a lathe (the holes wouldnt be any probly providing you worked in small amounts) but that to is unrealistic since the preasure aplied on rotor by the blade would warp the rotor just as much as the mill but in a different way. p-out

correct me if im wrong my knowledge on tool making is still growing

 

[takai]

you would have to use a mill with a large siezed bit. but milling a disc is unrealalistic due to the following
1. lets say a disc rotor is two mm thick. if you sat the disc on a perfectly flat surface and measured the amount the disc was warped (lets say it was point 25mm out) you would end up having to take half a mm off the thickness of the disc (a whole damned quater) deaming it unoperable anyway.

2. even with the biggest industrial (of course bigger ones can be made) size available for mills (wich as far as i know is about 200mm) the surface area of the mill bit would create enough heat through friction that it would end up warping it as soo as you stoped milling.

with that in mind its probably easier to use a lathe (the holes wouldnt be any probly providing you worked in small amounts) but that to is unrealistic since the preasure aplied on rotor by the blade would warp the rotor just as much as the mill but in a different way. p-out

correct me if im wrong my knowledge on tool making is still growing

Pretty accurate.
Dont bother milling or machining bike rotors, i normally just give them a scuff with scotchbrite to clean anything off and slightly roughen the surface. No real science behind it.

 

[Yowie]

i dont really know much about this topic
but wouldnt the pads wear in and sort of mould to the disk.
obviously a new rotor would be better.

also how would you machine a rotor?
i understand you could use a lathe for a car one but with the holes in it a lathe wouldnt do the job.

Car discs are machined on a specific machine, its sort of a cross between a lathe and a mill but more lathe like. Machining items with holes in it is no problem providing you don't over do the feed, most people use carbide bits these days and they stand up to just about anything. But a MTB disc is too small and cheap to worry about trying to machine, too hard to do on a lathe, too hard to do on a mill the only way I could see it getting done is on a suface grinder but most of them have a tolerance of +/-1mm.