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Shear scraping causing tear out?

Discussion in 'Getting Started' started by Fadi Zeidan, Jul 19, 2019.

  1. Fadi Zeidan

    Fadi Zeidan

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    I was turning dry pecan and every time I try to shear scrape the surface with a freshly sharpened bowl gouge I get really bad tear out. I can get better surface using a scraper at shear angle or doing a push cut. Any tips as to what I might be doing wrong?

    Gouge at an angle, top wing close to 1/16” from the surface, I notice resistance pulling the gouge towards me as if self feeding, no issue pushing it the other direction. I played around with the angle a little.
     
  2. Gerald Lawrence

    Gerald Lawrence

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    I have been turning a lot of pecan lately. Doing offering plates and counting prototypes and final number is up to 26 . What works best for me is a regular cut with a 3/8 bowl gouge except in the bottom. I come back with a negative rake round nose scraper. Tear out have not been a problem however with pecan there are so many crotches (not sure but that can be a problem) that the grain goes everywhere. Another problem with pecan is all the voids it has adding to problems and beauty.

    I tried wetting before scraping but that made the cut worse. So for me a good final cut with freshly sharpened gouge and if needed a shear scrape with neg scraper. Even then there will still be problem areas and sanding was the only solution I found.
     
  3. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Try dropping the handle lower ... between 45° and 60°. I use a Steve Sinner tool rest because the Robust rests don't let me drop the handle low enough. Also, I shear scrape rather high above centerline. Use a very light touch. If the tool is bouncing that suggests the piece might have warped. Doesn't matter if the wood is dry because internal stresses in the wood can cause dry wood to warp. I encounter that a lot when turning a basket illusion from dry maple.
     
  4. hockenbery

    hockenbery AAW Advisor Staff Member

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    I’ve not had this problem with pecan but have with other Woods from a particular tree.

    Some woods don’t shear scrape well.
    Moving In one direction may give a better surface.
    Try a steeper angle
    Extra light passes may improve the surface

    Too much pressure will often give a poorer result than light pressure.
    Some woods will take the extra pressure and scrape well.

    If shreds scraping isn’t giving a better surface - I stick with the gouge cut or maybe try a Hunter.
     
    Fadi Zeidan and Emiliano Achaval like this.
  5. Mike Johnson

    Mike Johnson

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    If all else fails apply a wood grain sealer to the piece and attempt your finish cuts.
     
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  6. Fadi Zeidan

    Fadi Zeidan

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    Thanks for the feedback. I’ll try these suggestions and see if I get better results. I can get good surface using other tools, or via push cut, I was trying to understand why my shear scraping via Ellsworth grind is causing tear out when it is supposed to eliminate it.
     
  7. robo hippy

    robo hippy

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    Well, I did this video a few years back, and it may explain a few things..


    View: https://www.youtube.com/watch?v=xeOhPqOsORs


    No two pieces of wood are alike, and this can include pieces from the same tree, not just with different species. I prefer dedicated scrapers with a burnished burr for the sharpest and most durable cutting edge. I was working with some Oregon Myrtle (California Bay Laurel) lately, and after experimenting around with it a lot, I found that I got the best surfaces with an 80 grit CBN wheel burr. Just because. Some times, a 600 grit gouge will leave the best surface. Some times you have to resort to 80 grit abrasives.....

    robo hippy
     
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  8. hockenbery

    hockenbery AAW Advisor Staff Member

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    It’s wood

    Sometimes the shear scrape pulls the fiber rather than shearing it
    Too much pressure, angle less than 45 from horizontal, direction of scrape, wing too far off vehicle
    The curve you are trying to scrape may prevent a good angle

    Dry wood shear scrapes better than wet wood
    I shear scrape the outside of wet turned hollow forms

    If I have a cove by the rim sometimes I can shear scrape it sometimes not.
    Vertical of the wing change a lot in a small distance.
    I like to think the nots are always due to the tightness of the cove but sometimes it’s just how locked in I get with the turning.
     
    Fadi Zeidan likes this.
  9. John Torchick

    John Torchick

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    I turn a bit of pecan for pen blanks. I use a roughing gouge and haven't had any problem. I'm aware that I'm doing different turnings than bowls.
     

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