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Clarification on scraper sharpening

Discussion in 'MACHINE RESTORATION & WAY SCRAPING' started by toms73novass, Jan 19, 2017.

  1. toms73novass

    toms73novass United States Swarf Registered Member

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    I have read mutiple posts that the blade should be sharpened to a negative angle of 93-95 degrees.

    Could you please indicate should it be sharpened like A or B. I thoughts that it should be B.
     

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  2. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    It should be A, negative rake.
     
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  3. easymike29

    easymike29 United States Active User Active Member

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    Drawing1.jpg
    Better yet...
     
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  4. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Yes, easymike29 shows the way most people do it, that way you have two edges to use before having to sharpen again...
     
  5. toms73novass

    toms73novass United States Swarf Registered Member

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    Thanks for the info, I'm sure I'll have more questions as I begin to experiment and learn.
     
    Last edited: Jan 20, 2017
  6. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    I must say though, that I use a different angle, maybe 3-5 degrees (85-87 degrees from the handle) and notice that the drawing shows much more bevel than what 88 degrees would really look like. A scraper with an angle like the drawing would be difficult to make cut in use.
     
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  7. easymike29

    easymike29 United States Active User Active Member

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    The drawing is purposely not to scale to emphasize the orientation. I might add that the the entire bevel is ideally on a 12" radius.

    Gene
     
  8. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Yes, Gene, there should be a radius in the cutting edges of the tool as seen in plan view. The radius changes depending on the work being done, and to some extent on preference and how the tool is held. A larger radius for rough scraping large flat surfaces, smaller radii for finishing, dovetails, etc.
     
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  9. Inflight

    Inflight United States Active User Active Member

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    I just made a quick video showing how I sharpen a carbide tipped scraping tool.



    Let me know if you have any questions.




    Matt
     
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  10. Uglydog

    Uglydog United States Active User H-M Supporter-Premium

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    Please note that in addition to the rake the radius also matters.

    Additionally,
    HSS is easier to sharpen than Carbide, at least on the wheels that most of us have on our bench grinders.
    HSS hones also well.
    Carbide costs more to begin with, and while a sharp edge may last longer, that should not mean that you need carbide in order to produce great scrapes.
    My opinion based on reading and my Minnesota scraping mentors.

    Daryl
    MN
     
  11. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    You can get a suitable carbide blanks for a few dollars or less if you look around, and braze or clamp them to a shop made handle. Honing the cutting edges by hand works fine, though Matt's setup is pretty elegant. The corners of the radius need to be intentionally dulled in both the vertical and horizontal planes so they do not dig and and gouge the work if the tool gets a bit off level.
     
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  12. Uglydog

    Uglydog United States Active User H-M Supporter-Premium

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    Bob Korves,
    You are likely correct.
    However, my emphasis is that it's ok to use HSS.
    It actually does work. And depending on your set-up it may be a better cheaper option.
    And yes, moving to carbide at some point is appropriate and good.
    But, we don't need to go nuts thinking and believing we must have carbide to begin our learning process.

    Daryl
    MN
     
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  13. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Absolutely, Daryl. At a get together last Sunday, Ulma Doctor (Mike Walton) made a scraping tool from a file in a few minutes on a ordinary bench grinder. That is not even HSS, it is carbon steel. It worked just fine, and we were scraping mild steel. It is still completely usable as a file. Hand scraping is pretty easy and cheap to get started with. Carbide will stay sharp longer and will cut harder materials, but it is not at all necessary for learning how to scrape. A year or two ago I did my first scraping with a scraper made from a file, also with Mike as my mentor. Mike has one made from a small file, for doing small and tight dovetails...

    We are conditioned by Madison Avenue, and often by our peers, to think that it takes the latest and most expensive equipment to do good work in our home shops. Nothing could be farther from the truth.
     
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  14. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    Well said, Bob!
     
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  15. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Check out this link of Dapra pricing for scraping equipment (with thanks to Ulma Doctor):
    http://www.moglice.com/Dapra/BIAXPriceList.pdf
    and you will see why Daryl chimed in. Their prices are outrageous, and their equipment is nice, but not at all necessary. One of the best things about scraping is that it can be done on the cheap, using brains and time and effort rather than money and more money. I think there is enough of a simmering nascent market for someone in the US to give Dapra some real competition.
     
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  16. bfd

    bfd United States H-M Supporter - Premium Content H-M Supporter-Premium

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    ulmadr and bob korves well said. the only thing is the thousands of scrapers (carbide tipped ) at the lb naval shipyard. with the fixture they provided in the carbide room. all sharpened to a 5 degree angle as bob indicated as an apprentice we got to sharpen the scrapers. yes there was enough scrapers to allow 20 apprentices to sharpen 8 hours a day 5 days a week and still have more to do grunt work for the peons the fixture set the radius don't know what it was bill
     
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  17. ericc

    ericc United States Active User Active Member

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    Hi Bob. Do you have a picture of this tool and the approximate angles? I tried making a scraper out of a file, and it did not do well. Actually, it was more like I bought a file at an estate sale that had been repurposed into a scraper. When I sharpened it, it didn't work. It made a few crumbs, but not enough to be useful.
     
  18. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Well, Eric, it was not my file and I did not grind it. It belongs to Ulma Doctor on this site and he might be able to help you with photos and angles. It looked like the angles were about the same as a commercial scraper, actually just one side was sharpened quick and dirty for the demo. It is important to get a good edge and to not overheat the file, or it will lose its hardness. Lots of BIG new machines were scraped in efficiently and accurately entirely with carbon steel tools before HSS and carbide came into use and before grinding entered widespread use for fitting machine parts. I understand that some of those old boys (and currently working scraper hands) could and can make chips that have a thickness of several thousandths, with smoke coming off of them, all day long, every day, by hand, for an entire career...
     
    Last edited: Feb 17, 2017 at 2:18 PM
  19. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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