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Will brake rotor iron make a good lapping plate?

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  • Will brake rotor iron make a good lapping plate?

    I have some 13" brake rotors that came factory on a 2012 GMC Yukon. From what I read they are G3000 grade cast iron. Suppose I cut the thick rim into pieces, turn, stress relieve, then surface grind them flat, would that iron make a halfway decent lapping plate? They are not drilled and/or slotted, and are ventilated.

    I also have plans dor the material, like making some test indicator stands for surface plates, so no big deal if it turns out to not make a good lapping plate. I will just repurpose it in another way.


    Andre

  • #2
    It should work perfectly. I'd normally use G2500 for its significant property of existing in my collection of bits of cast iron waiting to be used.
    Location- Rugby, Warwickshire. UK

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    • #3
      thinking about it, what makes a good lapping plate is something stable and soft enough for embedding....so why not? Heck, I've used scraps of AL before successfully.....depending on the objective, I think the important part is you get it really flat, grinding or better still scraping.
      Last edited by Mcgyver; 10-01-2016, 10:08 AM.
      in Toronto Ontario - where are you?

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      • #4
        I'll be home from Jersey later today, so I might try making a lapping plate this week. I'll report back. Think a bi-metal reciprocating saw blade will be able to cut it?

        Sent from my XT1053 using Tapatalk

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        • #5
          Are you making a lapping machine? I don't see how a rotor will work like a traditional hand lapping plate. See figure 13 on page 9 of: http://whoous.com/Machine%20Trades/T...of_Lapping.pdf

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          • #6
            Originally posted by Rosco-P View Post
            Are you making a lapping machine? I don't see how a rotor will work like a traditional hand lapping plate. See figure 13 on page 9 of: http://whoous.com/Machine%20Trades/T...of_Lapping.pdf
            Nope, I'm going to cut the rim into chunks and make very small plates. Ill also make some parallel blocks for general setups, and a few other tidbits. The rim on those truck rotors are fairly wide actually. I just need these lapping plates big enough to polish and remove grinding marks from small shop grade gauges I will be making. Nothing big at all, and they will probably only be 1.5" wide or so.

            Sent from my XT1053 using Tapatalk

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            • #7
              Excellent material, would benefit from multiple saw cuts to hold lapping compound longer.

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              • #8
                Originally posted by Andre3127 View Post
                .... Think a bi-metal reciprocating saw blade will be able to cut it?
                Aye

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                • #9
                  Originally posted by Carm View Post
                  Aye
                  Turns out it didn't even scratch the rotor before instantly dulling. A cutoff wheel on the grinder ate right through it though.

                  Sent from my XT1053 using Tapatalk

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                  • #10
                    I surface ground this segment flat and itll be useful for many things I'm sure. I think I'll make a few more, use them as spacer blocks for the mill, lapping plates, etc.



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                    • #11
                      The only requirement of a lap is that it is a material that is softer than the item being lapped. So using pieces of the rotor for lapping hardened gauge blocks SHOULD work just great. Especially if you remove any heat hardened skin that may be present from the rotor's original use with the surface grinding to true them up.

                      For lapping some mild steel it may not work so well depending on the surface hardness of the iron vs the mild steel. Which is why brass is often used for making laps for a lot of steel parts.
                      Chilliwack BC, Canada

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                      • #12
                        Originally posted by BCRider View Post
                        The only requirement of a lap is that it is a material that is softer than the item being lapped.
                        it also has to flat. very flat if that's what you impart on the work. The lap is not supposed to see the work and it really doesn't wear when done properly......its just a carrier for the abrasive. if what you are lapping needs to be flat, then your lap needs to be flat to at least the same extent. Hearing gauge making, I'm think it probably should be very flat - ground or scraped
                        in Toronto Ontario - where are you?

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                        • #13
                          I really won't do much lapping, and all that I would do is use super fine abrasive to remove grinding marks for longer life of precision parts that need to last. Such as a space block set I plan to make. I already have the tool steel, and they will be machined, hardened, ground, and lapped to within .0001" in size.

                          I have chunks of aluminum and brass I could use for laps, and although they can't be ground (I don't have the time to mess with coolants and special grinding wheels) I can scrape them in true.

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                          • #14
                            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. ;-)

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                            • #15
                              Originally posted by Mcgyver View Post
                              it also has to flat. very flat if that's what you impart on the work. The lap is not supposed to see the work and it really doesn't wear when done properly......its just a carrier for the abrasive. if what you are lapping needs to be flat, then your lap needs to be flat to at least the same extent. Hearing gauge making, I'm think it probably should be very flat - ground or scraped
                              True if someone is looking for a flat job to be done as with the gauge blocks mentioned here. But laps are used for lots of other things like lapping out cylinders with round internal laps, lapping pins with donut like outside laps and even for lapping odd shapes of any desired sort.

                              But you're right that there's more to it. I likely should have said something along the lines of "the only requirement for a lap other than having the proper shape is......".

                              Other than some hard condition use that may have produced a hardened skin on the outside surface I don't see why discarded rotors would not be good for scraping practice. If the scraper skids off the surface at the first stroke a little lovin' with an angle grinder should remove any hardened skin that's present.
                              Last edited by BCRider; 11-11-2016, 07:46 PM.
                              Chilliwack BC, Canada

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