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Will brake rotor iron make a good lapping plate?

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  • #16
    Originally posted by xraysur View Post
    Several people have suggested scraping the brake rotor material to make it flat. Would a brake rotor make a good source of material for scraping practice? Brake rotors are thrown away in scrap piles everywhere, so they are a reasonable source of free cast iron. Do they have other properties that make them difficult to scrape?

    I can't believe that I managed to use both scrape and scrap in the same paragraph. I hope I was able to use the correct forms of each word. ;-)
    The life of a brake rotor is a very bad one. It gets subject to thousands of heat cycles, including shock from rain hitting the hot rotor. When I put it on the lathe (photo below) HSS didn't even scratch it. In fact, it left a flat spot on the tool bit. I had to switch to carbide. Even a HSS recip saw blade hardly scratched it, I had to resort to abrasives to do any work to it. I do not know how soft the material is under the hard skin, but I bet it's too hard to scrape. Sorry to disappoint.


    (turning to get a fairly flat reference) https://www.instagram.com/p/BLPUGcOD...andre_shop3127

    (Cutting off with the zip wheel prior to surface grinding) https://www.instagram.com/p/BLrMvqPh...andre_shop3127

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    • #17
      For anyone interested. Check around the heavy duty truck shops in your area for a junk double disc clutch pressure plate assembly. I salvaged a nice chunk of cast iron from the floater plate (the plate that rides between the two clutch discs) of a clutch I replaced at work a few years ago. It's about 14" od with a center hole around 7" and 5/8" thick and cuts very nicely. I've been screwing around scraping a small straight edge out of a chunk I sawed out of it. It seems to be pretty workable.

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      • #18
        Originally posted by paul463 View Post
        For anyone interested. Check around the heavy duty truck shops in your area for a junk double disc clutch pressure plate assembly. I salvaged a nice chunk of cast iron from the floater plate (the plate that rides between the two clutch discs) of a clutch I replaced at work a few years ago. It's about 14" od with a center hole around 7" and 5/8" thick and cuts very nicely. I've been screwing around scraping a small straight edge out of a chunk I sawed out of it. It seems to be pretty workable.
        I don't think it's standard to have two clutches and a plate between them, although I know they exist for race applications. A flywheel might work fine though, if it doesn't have hot spots from riding the clutch.

        Sent from my XT1053 using Tapatalk

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        • #19
          Dual disc clutches are very common in heavy duty trucks. By heavy duty I mean OTR semi trucks, dump trucks, etc.

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          • #20
            I use spent brake rotors as expendable lapping plates driven by the Lapmaster.

            The rotors are retained by magnets. They are simply set down on the original platen/ lapping plate. Any eccentricity is a bonus to distribute grooving as the outer edge bears the lion's share of abuse. This set up is nearly as useful as a Glendo diamond lapping machine.

            I've got a half dozen rotors that have been charged and used with different grit. They work great for touching up cutting tools of all types, or any time a controlled material removal is needed. The work piece often manipulated free hand.
            The brake rotors are readily shaped (flat or other) by working two against each other.

            For truly flat work, the original Lapmaster platen and work holders are employed.
            Last edited by CalM; 11-11-2016, 10:41 PM.

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            • #21
              Originally posted by Andre3127 View Post
              The life of a brake rotor is a very bad one. It gets subject to thousands of heat cycles, including shock from rain hitting the hot rotor. When I put it on the lathe (photo below) HSS didn't even scratch it. In fact, it left a flat spot on the tool bit. I had to switch to carbide. Even a HSS recip saw blade hardly scratched it, I had to resort to abrasives to do any work to it. I do not know how soft the material is under the hard skin, but I bet it's too hard to scrape. Sorry to disappoint.


              (turning to get a fairly flat reference) https://www.instagram.com/p/BLPUGcOD...andre_shop3127

              (Cutting off with the zip wheel prior to surface grinding) https://www.instagram.com/p/BLrMvqPh...andre_shop3127
              That's what I was concerned about too.

              Truth is that new jobber no name brand rotors are cheap to buy. And being unused won't have all these possible heat shock related issues.
              Chilliwack BC, Canada

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              • #22
                Originally posted by Andre3127 View Post
                The life of a brake rotor is a very bad one. It gets subject to thousands of heat cycles, including shock from rain hitting the hot rotor. When I put it on the lathe (photo below) HSS didn't even scratch it. In fact, it left a flat spot on the tool bit. I had to switch to carbide. Even a HSS recip saw blade hardly scratched it, I had to resort to abrasives to do any work to it. I do not know how soft the material is under the hard skin, but I bet it's too hard to scrape. Sorry to disappoint.
                interesting. For my part I didn't advocate scraping brake rotors, I advocate scraping or grinding as way to get things flat for use a lap. what speed where you running? they're easily turned with carbide afaik.

                If they really are that hard that is a reason why they'd not be the best choice as lap....the abrasive has to imbed; stability (staying flat once made flat) and being soft enough for imbedding are the entire reasons for using CI in the first place. I'm fully supportive of experimentation, but if you just want a lap a hunk of durabar would been the way to go imo
                in Toronto Ontario - where are you?

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                • #23
                  I keep a few brake rotors kicking around under the bench or saw. They make good sacrificial plate for jigging up some awkward to hold parts. I have one drilled to fit my Rotary Table and bolt things to the smaller hub part. All the ones I have are non vented. As BCRider says even new pattern ones are cheap.

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                  • #24
                    40+ years in the auto repair bidness. Rotors are so cheap now I hang new ones every time they start to pulsate on my own vehicle. My time is worth more than the cost to buy new ones. All my techs have piles of rotors stacked up waiting for the scrap man to carry them off. We will never wear out our brake lathe.
                    Joe

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