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thought id have a play around with my old disc and see if its poss to make it presentable, the disc was in pretty bad shape, i used my air palm sander on it with 180 grit pads then 400 grit, it looks pretty good considering ive only spent half hour on it.
before..


after..
 

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um...yeah...make sure you take the disc to a machine shop and have them check it on a lathe....hopefully you didn't introduce any high or low spots on the disc or warping from the sander.
 

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Discussion Starter #3
no i was pretty carefull mate, if i can sand a flat peice of soft alloy without introducing high spots then stainless shouldnt be a prob, im gonna fit it to my bike and see how it faires under braking.
 

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quote:Originally posted by RetroTony

no i was pretty carefull mate, if i can sand a flat peice of soft alloy without introducing high spots then stainless shouldnt be a prob, im gonna fit it to my bike and see how it faires under braking.
high spots in discs come from localized heat not from the actual sanding discs. If you focused the sander on one spot more than the others sufficient to build heat in that area then the disc could warp. I would still check it on a lathe or a brake cutter.
 

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or sand it on a flat table.

i cant see that using a palm sander is really going to damage it.
 

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quote:Originally posted by Geeto67

quote:Originally posted by RetroTony

no i was pretty carefull mate, if i can sand a flat peice of soft alloy without introducing high spots then stainless shouldnt be a prob, im gonna fit it to my bike and see how it faires under braking.
I would still check it on a lathe or a brake cutter.

The spec for parallelism is pretty much accepted to be 0.0001". Please enlighten me why any form of lathe would be required or preferred to check this geometric constraint. I actually know how to check it and the correct simple tool one would use.


Now had you stated a turning device should have been used to simultaneously grind both sides to assure near absolute parallelism... I'd not have an issue with such an assertion. Do you know what symptom an out of parallel disc will manifest?
 

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now see.. I'd buy this if you were talking about the disc being warped or made out of parallel from use and you were chastising him for claiming to have fixed it by hand

yet even then.... a lathe would only be useful for checking to see if it were 'unwarped'..... still pretty much useles for confirming parallelism

now I agree one could actually high or low spot a brake disc....0.0001" doesn't require too much effort to move... no significant... perhaps not any heat would be required or resulting

however.... to change the crystaline structure as you are implying.... man that thing would have to get hotter than you obviously realize and would be much more likely to happen on the bike than off it and being barbarically stroked with hand tools


I certainly did not see any signs of such overheating in the before (which would be where you'd see them unless Tony tried to nuke them) or after pix



quote:Originally posted by Geeto67

high spots in discs come from localized heat not from the actual sanding discs. If you focused the sander on one spot more than the others sufficient to build heat in that area then the disc could warp. I would still check it on a lathe or a brake cutter.
 

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Surface plate and height gauge off mounting flange, you can check both sides without flipping it over. Micrometer will only tell you if its same thickness all round.
Lathe would rely on bearing tolerance so not really accurate enough IMO

PJ
 

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car rotors usually develop their warps due to hard braking down to a stop, and then the (hot) brake pads continuing to be pressed onto that one spot on the rotor. then you get the "thump thump thump" brake feel. even after a careful skimming on a lathe, the rotors re-warp shortly after the brake "service" is done. if hack man doesn't see tell tale signs of the dreaded local cook, then your rotor is prob. o.k. but can't you find a new one? i've been doing work with my hands most of my life and have a pretty good feel for "flat". but .0001" accuracy would have me a bit intimidated even with 400 grit on a palm sander.
-parks
 

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since I'm sure this is one of those times somebody almost knows what they are geeting about.....

I'll go ahead and lay it out

parallelism is simply measured with a micrometer


it does not take much to cause problems


and the initial symptom is not shaking or pulsing...

but a low brake pedal or lever that is most noticeable after an extended run without using the brakes..... yet it will pump up firmly and stop well

may not even be noticeable around town....

seen it kick many allegedly 'ace mechanics' keyboard asses

cpj... the precision/omg$$$ taper bearings in my harrison knock off do not have enough play anywhere that I can measure it


I do not really have any opinion about the pictured refurb job other than I'd have deglazed it while on the bike if I thought it may be junk

If not and pricey/rare... it would have been set up and both sides properly machined or ground at the same time

otherwise I wouldn't have bothered
 

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Discussion Starter #11
chill out boys, i fitted the disc last night and its fine, no high spots, braking from low and high speed is perfect.
there is no machine shop i can find that will 'skim' a stainless disc, it wrecks there tools aparently, nor does anyone have a double surface grinder around here.
 

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Mr. Hackasaw has once again added an adjective to my vocabulary. Thank you:D

I wrecked a pair of rotors with a lathe once. Between tool chatter and not understanding parralellism we made some pretty junk. I was much younger then.

There's a guy that surface grinds stainless rotors on eBay. Thought someone on here knew him in real life? Doesn't sound like it's an easy or common operation just asking around trying to find someone local to salvage the rotors I screwed up.
 

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When I worked at a shop in Milwaukee, we used to chuck the disc up in the big lathe and hit it with a body grinder while it was spinning. It cleaned them up nice and left a shiny finish that seemed to work well. We had lots of happy customers.

Ken
 

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The guy on ebay uses a rotary surface Blanchard grinder. I'm not sure what kind of tolerance he can hold, but I had mine drilled and ground by him and they worked very well.
 

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I read something even more rediculious than implying 0.0001" is the max out of parallel for a brake disc

it went like this

'a warped rotor cannot be parallel'

which has only been topped by the donkey llama trying to convince folks on the net that drum brakes have more stopping power than disc brakes but would have no idea how to prove it other than "brake tests"


even if one doesnt have the math.... everyone knows they'd have them on F1 cars & GP bikes.... although highly refined and evolved from drum brakes form after their final curtain call years ago


has anyone else here passed the ASE's brake test?
 

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Nope, whats ASE?
Did British version long time ago for MOT testing
0.0001" out of parallel?
Not sure Honda spec, know they allow 0.004" runout.
As for lathe bearings, its going to depend on machine temperature and prior use.
If yours have been changed (sounds like it)and not abused should be fine, but you must have some clearance in there for lubrication.
I did train as precision machinist, close tolerance was +0.000mm/ -0.001mm, wide tolerance, 5 microns (+/-2.5)
We were using Harrison or Colchester tool room lathes.
Single point wasn't a problem until 'they' halved production time

PJ

PJ
 

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well I don't know of any brake disc specs that even allow for 0.001" out of parallel

runout is a completely different beast

my lathe spindle.... as well as my mill

runs dual paired timkens

and they are, of course, preloaded

but it still will not single point disc brake rotors and have them end up parallel within acceptable tolerance

runout less than 0.004"?

no problem even on a bad day with haphazard setup

now my little 10k runs a shimmed bushing and seperate thrust bearing

that again is a different beast
 

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I made the mistake of purchasing some reground stainless rotors a few years back- they were perfectly flat but sides were not perfectly parallel, one was so bad you could barely hang on to the bars when you applied the brake, seems like it was about .002" off. The better of the 2 was .0008" out of parallel and it still pulsed. I did get my money back but wonder if there is anything better out there today.
 

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at some point before they 'pulsate'

the only tell tale will be a low lever or pedal that will 'pump up'

even if barely perceptible and the operator accepts it for normal or maybe never notices

hair splitting? maybe, but, if you are a tech at a dealership where there may be a perfect example for an owner to compare to

throwing un-needed hydraulic parts at the problem could force you to do some fancy pencil whipping to keep your money and stay in good grace with those who pay you






I suppose
 
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