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Grinding vs Scraping?

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  • Grinding vs Scraping?

    This isn't really "home shop" unless you have a grinder, but... I was recently watching a YouTube video where the person was surface grinding his part, followed by scraping. One of the commenters after the video asked why the scraping was necessary (as if they didn't notice the print on the surface plate). I said that scraping can work to a closer tolerance. Another poster said that was a bunch of BS and modern grinders are superior to scraping an every way. All I know is, I saw the print when he blued the surface plate in the video.

    What do you think? I'm just asking because the debate really bothered me -- there is a lot of history on the subject.

  • #2
    I am just a hobbiest BUT the scraping Also adds cavities for oil and better lubricates and reduce stiction
    Ed
    Agua Dulce, So.California
    1950 F1 street rod
    1949 F1 stock V8 flathead
    1948 F6 350 chevy/rest stock, no dump bed
    1953 chevy 3100 AD for 85 S10 frame have a 4BT cummins motor, NV4500
    1968 Baha Bug with 2.2 ecotec motor, king coil-overs,P/S

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    • #3
      I've never seen a grinder that could work closer than half a tenth, Its gonna look like a banana on the surface plate. Do they make grinders that can work to millionths and get a perfect print on the surface plate?

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      • #4
        I'm thinking that there are probably "modern grinders" that can work to a smaller tolerance. But such are likely not the sort of machine to be found in a home or smaller commercial shop. So if the goal is to have a flat surface that we KNOW is flat a trip to the surface plate to at least check the results is warranted. And a little touch up with some hand scraping is not out of the question. And that would appear to have been the case with the grinder used in the video from your comment about the dye print.

        Of course then I start losing sleep over how calibrated my surface plate truly is....
        Chilliwack BC, Canada

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        • #5
          there are lots of home shop grinders out there......but what's a "modern" grinder? Mine's a Norton

          "superior in every way", words of a fool. He either doesn't fully understand both or, is inexperienced or just lacks imagination.... its the fool in such a position who makes pronouncement and thinks in such absolutes

          There's a long laundry list of instances where scraping is going to be superior, and ones where grinding is .....assuming time is one of judging criteria and of course assuming a grinder.

          The intelligent person doesn't view them as completion but as different techniques. He understands both and can apply the best technique to the task at hand given available resources (including time)

          Last edited by Mcgyver; 02-01-2020, 12:11 PM.
          .

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          • #6
            Originally posted by BCRider View Post
            Of course then I start losing sleep over how calibrated my surface plate truly is....
            Pay for shipping both ways and you can borrow my repeat-o-meter

            Dan

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            • #7
              Originally posted by Mcgyver View Post
              there are lots of home shop grinders out there......but what's a "modern" grinder? Mine's a Norton

              "superior in every way", words of a fool. He either doesn't fully understand both or, is inexperienced or just lacks imagination.... its the fool in such a position who makes pronouncement and thinks in such absolutes

              There's a long laundry list of instances where scraping is going to be superior, and ones where grinding is .....assuming time is one of judging criteria and of course assuming a grinder.

              The intelligent person doesn't view them as completion but as different techniques. He understands both and can apply the best technique to the task at hand given available resources (including time)
              Thank you, that is exactly what I was feeling... I've never seen a part come off a grinder and make a perfect print. The speaking in absolutes really is what bothered me.

              I wonder, what about the internal parts of hard drives? Those things approach a level of perfection only seen in the space program. I wonder it those are produced by grinding, on an industrial scale? The discs are often equal to "lab grade" surface plate perfection.

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              • #8
                I find today that many folks love to think in terms of absolutes. We see this on the news all the time with how groups have little to no room for tolerance of others. The old "yer either with us or agin us" attitude. The grinder guy is clearly one of those and has not worked with a lot of machines. Or at least does not understand how tolerances build up to confound us.
                Chilliwack BC, Canada

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                • #9
                  Originally posted by BCRider View Post
                  I find today that many folks love to think in terms of absolutes. We see this on the news all the time with how groups have little to no room for tolerance of others. The old "yer either with us or agin us" attitude. The grinder guy is clearly one of those and has not worked with a lot of machines. Or at least does not understand how tolerances build up to confound us.
                  Yeah, you're right. I notice that too. It's really a downer because it discourages learning and progress. It discourages sharing and conversation. I actually attribute it to the Devil himself, because its just false pride. Causes a lot of destruction.

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                  • #10
                    my guess for hard drive platers is that they're cast on liquid, like glass is. In fact most HDD platters are glass. They're then coated by vacuum deposition and buffed for smoothness and flatness.

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                    • #11
                      Originally posted by Mcgyver View Post
                      there are lots of home shop grinders out there......but what's a "modern" grinder? Mine's a Norton

                      "superior in every way", words of a fool. He either doesn't fully understand both or, is inexperienced or just lacks imagination.... its the fool in such a position who makes pronouncement and thinks in such absolutes

                      There's a long laundry list of instances where scraping is going to be superior, and ones where grinding is .....assuming time is one of judging criteria and of course assuming a grinder.

                      The intelligent person doesn't view them as completion but as different techniques. He understands both and can apply the best technique to the task at hand given available resources (including time)
                      This, right up there. A person that decrees such absolutes makes obvious their inexperience of the subject matter. I suppose the machine tool builders that STILL scrape their machines and charge a premium for it are stupid and living in the past... And the shops and people that love them, equally ignorant...?

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                      • #12
                        Originally posted by mattthemuppet View Post
                        my guess for hard drive platers is that they're cast on liquid, like glass is. In fact most HDD platters are glass. They're then coated by vacuum deposition and buffed for smoothness and flatness.
                        Lapping a method used long before the space program came into being.

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                        • #13
                          Originally posted by Zahnrad Kopf View Post

                          This, right up there. A person that decrees such absolutes makes obvious their inexperience of the subject matter. I suppose the machine tool builders that STILL scrape their machines and charge a premium for it are stupid and living in the past... And the shops and people that love them, equally ignorant...?
                          But....if it's on YouToob is must be true. After all the guy's got 10 trillion likes and a Patroon account. That makes him an expert, doesn't it?

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                          • #14
                            Originally posted by Zahnrad Kopf View Post

                            This, right up there. A person that decrees such absolutes makes obvious their inexperience of the subject matter. I suppose the machine tool builders that STILL scrape their machines and charge a premium for it are stupid and living in the past... And the shops and people that love them, equally ignorant...?
                            Yes, this. I saw a robrenz video in which he repaired Tom Lipton's level. He had just completed re-scraping the ways on his grinder. The results as measured were within 20 millionths. This was with a lab-grade surface plate, an electronic indicator, and precision-ground stones. He flaked the surface anyway, and the results didn't change.

                            Being that robrenz had 50+ yrs of experience, I'll go with what he says. Ditto Tom Lipton.

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                            • #15
                              Originally posted by reggie_obe View Post

                              But....if it's on YouToob is must be true. After all the guy's got 10 trillion likes and a Patroon account. That makes him an expert, doesn't it?
                              Yeah, it doesn't count if the guy has decades of experience and owns the shop, making money off his own work!

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