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Thread: Want to get into Hand scraping

  1. #1
    BillH Guest

    Post Want to get into Hand scraping

    Well, I searched the archives, and it appears I missed out on a great group buy on that book about reconditioning machine tools.
    For those of you who bought the book, and done some hand scraping, can you post some pics of your work? It is a skill I really want to learn.
    Now I understand it is for getting surfaces really flat. So how about the checkering that was done on south bend lathes, and some bridgeports? Is that another type of scraping? Or is that the natural look of scrape marks?
    I have an urge to scrape some steel plate, perhaps one day use it to restore lathe beds.

  2. #2
    Join Date
    Jul 2002
    Posts
    4,309

    Post

    Here, it's call flaking and other than appearance it holds oil. There is a way to hold the scraper that produces that effect. I havent done all that much of it myself.

  3. #3

    Post

    Bill

    A surface can be scraped flat, but for bearing surfaces like lathe beds you want a "pebbled" surface - so to speak with equally spaced high and low spots - the number per square inch would be dependent on the quality of the work. In effect, we want a controlled roughness so the two bearing surfaces do not experience "stiction" (almost a vacuum welding effect similar to the "wringing" of gauge blocks) to one another. Hard drive makers found this out the hard way, machine builders have known it for a hundred years.

    Granite flats naturally have air pockets around the hard quartz particles where the softer material breaks off during the grinding operations and leaves a slight depression around the "Quartz island" - this is why flat surfaces do not stick to granite flats.

    The "frosting" on ways you speak of can be as scraped or it can be quite artistic to the point where a particular design is a tradmark of a particular man's work. The Half-moon crescent design is done with a certain model Dapra power scraper - any idiot can do it. These frosting designs are purely decorative and serve no useful function - but some sure are beautiful!

    If you want to try it yourself, practise on some cast iron angle plates - they are cheap and easy to come by. Buy the Connolly book and get started.

  4. #4
    BillH Guest

    Post

    I wonder how deep those crescent marks are, they sure are a neat guage to determine wear.

  5. #5

    Post

    Bill

    Pardon the pun, but "they barely scrape the surface" (ha, ha)

  6. #6
    Join Date
    Apr 2001
    Location
    Maine
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    6,972

    Post

    I like Thrud's idea of practicing on a cheap cast iron angle plate. The angle plates made in India may actually be useful for something after all, and you can turn them into a worthwhile product.

    The Machine Tool Reconditioning book may not be the best place to start; for one thing, it's pretty expensive. Lindsay Publications has, I think, some relatively inexpensive reprints of how to do scraping that might be a better source of basic information.

    Quick course:
    Basically, all you need is a reference surface plate, a tube of Dykem Hi-Spot Blue or equivalent, and an old file ground to a large radius on the end, square to the top and bottom faces of the file, for your scraping tool. Smear a THIN film of blueing on the surface to be scraped, place it on the surface plate, move it back and forth an inch or two a couple of time, lift up, and you should see some bright spots where the blueing got rubbed off. Take your scraper and scrape those down, smear the blueing back over those spots, and repeat. And repeat. And repeat. Etc.
    ----------
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  7. #7
    Join Date
    Oct 2003
    Location
    mesa, az
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    I don't know much about scraping myself but the older guys I work with do it for a living. I was told by them that the crescent shape that they put in, is done for the lubrication. I guess the ways can hold a little more oil. I have watched them scrape and put in the crescent shapes many times and it is truely an amazing thing to see.
    FuQ

  8. #8
    Join Date
    Sep 2003
    Location
    Louisville, KY
    Posts
    806

    Post

    Thrud's suggestion about practicing on an angle plate is excellent.
    By all means obtain a copy of Connelly's "Machine Tool Reconditioning", it is the cheapest tool you will buy, for value recieved.
    The way to treat the angle plate is to; apply marking medium to the surface plate, place the surface to be spotted on the plate and move 1 or 2 strokes about 1/2" back and forth in straight line, take it off, scrape the blued spots, clean and debur, respread the marking medium on the surface plate, repeat the foregoing procedure, and so on until the surface is scraped in. The proper procedures are discussed at great length in MTR.
    Harry Bloom

  9. #9
    Join Date
    Jan 2003
    Location
    Dallas, Texas
    Posts
    441

    Post

    If you can BORROW a copy of the Michael Morgan
    Scraping Video, it will really set you on the right path.I never rec'd my order,so I can't recommend buying from him, but it's a good
    instructional. I have found a good Sandvik or
    Dapra carbide scraper is the way to go, and
    learn to sharpen with a diamond wheel. Find a real scraping hand and see if he will give you
    a lesson or two. And lastly practice, practice,
    practice.

  10. #10
    BillH Guest

    Post

    Thank you guys for all the advice, when I get a chance, I will do these things, perhaps sooner than I thought.
    You know, I bet the airport screeners would not like a hand scraper!
    Im on the road at the moment, this hotel actually has high speed internet hookup in each room.

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