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  • Scrapeing?

    Here's another dumb question. What exactly is the process of lathe bed scrapeing? I'm not sure I even spelled it right. Is this really a hand process?

    Jim Wilson

  • #2
    Jim,

    To generate the first three precision flats, THREE cast iron plates were hand shaved with a chisel like scraper to match each other.
    To have three plates all match, each must be perfectly flat.

    From these master plates special masters for dovetails and flats can be made.

    A light coat of prussian blue or other marker is put on the master plate.

    The surfaces are lightly rubbed togather.
    The high spots show up as light blue, and you scrape them off, repeating the process, until a uniform pattern is achieved.

    Also the proper alignments must be held with indicators or gages.

    This craft takes years of experience to become proficient.

    There are some books on Ebay regularly about the craft.

    One excellent book called Machinery Reconditioning was out some years ago.
    I lent mine out never to see it again.

    mite

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    • #3
      Mite;

      That book is still advertised in one of the Village Press mags. $92. I believe.

      Comment


      • #4
        The book is Machine Tool Reconditioning, subtitled Applications of Hand Scraping. It is privately published, and I saw a thread on one of the metalworking Usenet groups that suggested the publisher saves up orders until he has enough to justify a press run, and blatantly ignores the federal law requiring mail order vendors to notify their customers if they can't whip within thirty days. I got my copy in a few weeks, but some posters had waited months.

        There was a multi-part article starting in the Nov. '97 HSM about reconditioning a shaper vise using hand scraping techniques. It gave a pretty good explanation, and had better pictures than the book, but of course not nearly the depth of detail as in the book.

        Another thing to keep in mind is that you can only scrape your lathe bed if it is cast iron. Hardened or chromed ways need not apply.

        Comment


        • #5
          Uncle Dunc:
          I beg to differ a tad. You can scrape hardened and chromed ways with carbide. This sometimes is required in specific applications. I will agree it is very rare, but it does happen.

          Jim:
          The scraping process is done by hand - it has never been accomplished by any machine to date.

          Flat is a relative term. If the surface plates were really flat they would "wring" together like gage blocks. Granite plates are only flat on the exposed quartz grains - similar to an island in a lake. This is why gage blocks do not wring to the granite flats. Only optical "flats" and Grand Master gage block are close to "flat" - and in absolute (molecular level) terms even that is an oxymoron.

          What scraping does is try to present sufficent "high points" to give flat bearing surface on a statistical averaging basis. This allows for "true" movement long its surface without 2 equally "flat" pieces fron wringing together - in the case of the ways this allows for pockets of lubricant and hydrodynamic lubrication (floating in oil) resulting in smoother operation and less wear.

          Scraping is a good thing. If you decide you would like to try your hand at it you can practice on cast iron angle plates. Buy cheap ones that are just machined and if you do not have a ganite flat a 12x9 will do the job (around $40). Get a book on it and start playing. It takes time - patience is the keyword here. Guys that are really good at it often design their own "personal signature" pattern - a work of art!

          Have fun

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          • #6
            >> You can scrape hardened and chromed ways with carbide.

            I thought that might be possible and was going to suggest it, but I'd never heard of anyone doing it. Plus it sounds really, really boring. Not an ideal project for a novice scraper.

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            • #7
              http://www.csgnet.net/toolroom/scrape1.htm

              Comment


              • #8
                Thrud,

                Good to see someone else appreciates the usefulness of a hand scraped surface.
                Some other guy, in some other chat room went on and on about the uselessness of scraping for lubrication.
                They deleted out my reply (after I really got swelled up fingers typing it).
                A freshly scraped machine is to me, a thing of beauty (next to that "shiney" stainless steel).

                mite

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                • #9
                  A hand scraper is a very useful thing in a machine shop even if you never rebuild a machine. Just the thing for cleaning up edges or holes before gringing. I've been "taking lessons" with a fellow who is in his late seventies and still going strong. Scraping is good exersise for mind and body and helps develop personal honesty. It's easy to scrap a block of cast iron so it looks pretty, but it is somthing elese again to make it square and flat. Last time I was over, my mentor showed me a gib from an import mill, it looked good but when spotted turned out to be a joke! I'm not slamming MIT machines, but I'm sure glad he has taught me how to tell decoration from the real thing. A real scraped surface is a thing of beauty and a joy forever!
                  Bye the way, used book dealers can get you a good used copy of Connley's book for about $40 US,
                  Chears!
                  hms50
                  hms

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                  • #10
                    Scraping is a poor man's surface grinder, in fact better if done correctly. It is also a bit more portable and not limited to size of the machine.

                    Grinding leaves sharp crests, scraping takes off those sharp crests. Even nicely ground surfaces have those sharp crests. One might wonder about lapping to a perfectly flat and smooth surface, but this has dissadvantages also. Ever been around gage blocks, they stick together.

                    Scraping is done to a percentage of bearing, it has highs and lows, with a light oil film scraped surfaces almost seem to glide. This is the reason a Bridgeport mill is so smooth compared to a ground way machine.

                    There are power scrapers, Biax comes to mind. I've never seen one, let alone use one, what scraping I've done has been hard work at times.

                    Here's a web site for you to look at, ran by a Mr. Morgan. He had some health and business problems, got behind in his orders. Bunch of fellers were ready to lynch him, but it seems he's shipping ordered goods now. But he has some info on his web site that you might enjoy.

                    http://www.machinerepair.com/

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