Skimming Brake Discs (Rotors)

[angryfarang]

Can anyone help me?

I'm looking for a place that can skim a set of brake discs.

I spent hours on them yesterday with wet and dry paper and there are still train tracks going around them. It looks like the previous owner ran them with knackered pads.

I checked the thickness of the discs with a micrometer and they are 5.0mm, so there's plenty of meat on them.

I'd like to get them skimmed. Can anyone recommend a place I could send them?

Cheers.

[VocalNeal]

You are about the 4th person in the last week asking for location specific information without stating your location? So it is almost impossible to help you.

Just saying!

That being said any decent machine shop will do them for you. So wherever you are there is a machine shop somewhere near.

Edited November 19, 2012 by VocalNeal

[angryfarang]

Doh! Sorry I'm on Koh Samui - where's it nearly impossible to get anything done properly. lol.

[Hog Head]

I have never had any luck in machining a bike rotor, even using a surface grinder as I can always feel pulsing through the lever

Give it a go on a surface grinder with a magnetic table, or Blanchard type grinder but be prepared to buy a new one

Brakes are highly overrated anyway, and rotors are unimportant and far too expensive

[angryfarang]

I have never had any luck in machining a bike rotor, even using a surface grinder as I can always feel pulsing through the lever

Give it a go on a surface grinder with a magnetic table, or Blanchard type grinder but be prepared to buy a new one

Brakes are highly overrated anyway, and rotors are unimportant and far too expensive

dam_n. A new front brake disc is around 10,000 Baht for my bike.

[angryfarang]

Maybe I'm using too fine sandpaper? I'm using 600. Should I try with something more abrasive and then work up?

[VocalNeal]

Doh! Sorry I'm on Koh Samui - where's it nearly impossible to get anything done properly. lol.

Living on a, not quite, island paradise

Mostly what I see here in Bangkok is car discs being skimmed and run-out is less of a problem.

AF are your discs warped or simply showing signs of scoring? If only scored I wouldn't worry about them, sure it will take a bit longer for the pads to conform to the discs but...

If you are racing then.....

[angryfarang]

Hey Neal,

It's just really some scratches running around the disc. They're not too deep, so like you said, nothing to be worried about. I just wanted them perfect and looked on-line about skimming discs.

I'll whack them back on.

Cheers.

[transam]

Minor imperfects will be taken up by the pads. New pads will not be as efficient until they bed into the irregularities. On a car there is a bit of meat to machine off a disc but a bike . Personally l would buy new or not worry about your minor imperfections unless you feel stuff through the levers. .

[angryfarang]

Thanks for the replies. I'll just whack them back on, they've cleaned up very well. I'm new to playing around with bikes, plus I have OCD - so I want to get everything perfect!

[loserlazer]

I have see what you are looking for in car tire shops.

They have a machine to do that automatically.

What i have seen; they just placed the discs to the machine and they were like new out of it.

Check tire shops i hope we are talking about the same thing and it also works for bike discs.

I always change my discs if i see irregularities on it no matter how much it is.

Lost a good friend before due to a broken disc before so i take it serious.

Sent from my GT-N7100 using Thaivisa Connect App

Edited November 19, 2012 by loserlazer

[karlos]

10,000Baht well spent IMO

As you know there's very little material on bike discs and the tolerance between new and worn-out are small, so small that any machining would take you close if not pass the 'worn-out' tolerance.

As mentioned above, if you can't feel any warp/pulsing then stick with the discs you have without machining them. Just take a little more time to ensure new pads fully seat into the 'minor' groves before expecting the brakes to function fully.

Edited November 19, 2012 by karlos

[Lickey]

original equipment discs will have the minimun thickness stamped on them somewhere, spurious discs,probaly not,

Guessing from OPs posts he has a twin disc large bike, and most bikes from 1990 on have floating discs, whether these can be skimmed or not i dont know??

If they are floating discs they will have bobbins [looks like round washers] between the disc and the fixed center part, These get jammed with brake dust and road dirt, when this happens the disc wont "float" through the caliper, easiest way to clean these is shape a piece of wood into a taper so it fits the bobbin, with WD40 spray the bobbin and turn it till the crap runs out of it, dont wiggle the bobbin too much, doing this flatten off the wavy spring washers either side,

Otherwise as others have said, dont worry to much about the grooves, with new pads to help them bed in quicker, put a little pressure on the lever at crusin speed for 5secs every now and then..

[Neilly]

Doh! Sorry I'm on Koh Samui - where's it nearly impossible to get anything done properly. lol.

There's a small machine shop on the RH side going towards Lamai from the immigration office traffic lights...about 500mtrs down. I had some wheels modified there so they would fit my WR and he did a good job.

One problem you might find is that some rotors need to be ground and can't be skimmed/machined...depends on what they're made out of

[angryfarang]

original equipment discs will have the minimun thickness stamped on them somewhere, spurious discs,probaly not,

Guessing from OPs posts he has a twin disc large bike, and most bikes from 1990 on have floating discs, whether these can be skimmed or not i dont know??

If they are floating discs they will have bobbins [looks like round washers] between the disc and the fixed center part, These get jammed with brake dust and road dirt, when this happens the disc wont "float" through the caliper, easiest way to clean these is shape a piece of wood into a taper so it fits the bobbin, with WD40 spray the bobbin and turn it till the crap runs out of it, dont wiggle the bobbin too much, doing this flatten off the wavy spring washers either side,

Otherwise as others have said, dont worry to much about the grooves, with new pads to help them bed in quicker, put a little pressure on the lever at crusin speed for 5secs every now and then..

Single Disc Front Brake from CB250FT. Min thickness stamped on disc: 3.5mm. Original thickness 5.5mm. Current thickness (measures with micrometer) is 5.0mm. I'm going to forget about skimming the disc and go at them again with some 200 grit and then work up to 600 grit. I'm pretty sure I can get the marks out. If not, I'll just use them.

Thanks for all the advice.

[VocalNeal]

... plus I have OCD - so I want to get everything perfect!

Ah Grasshopper. You must learn to accept imperfection.