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Thread: Cutting a donut

  1. #1
    Join Date
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    Default Cutting a donut

    I may have the opportunity to cut out a bunch of wooden "donut" shapes. Approx. 15" in diameter with a 2" cross section diameter. It would need to be a two-sided cut, which I think I can figure out. Probably four profile cuts with a round over bit. Two per side.

    What I'm not sure of is hold down when the piece is flipped over. Using a round over bit I can't leave tabs. Any suggestions would be appreciated.
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  2. #2
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    Keith,
    Maybe worth reading?
    http://forum.vectric.com/viewtopic.php?f=2&t=26073
    Moulding Toolpath is a Profile cut, so maybe leave tabs on first side?
    scott
    Scott Plaisted
    Desktop/spindle/VCP 8.5**
    Maine

  3. #3
    Join Date
    Sep 2006
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    cnc routing, portland or
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    unless the roundover is special or you can't get a bit that size I would do them on a router table it is faster and easier. cute donuts and while they are cutting round them over on a router table.

  4. #4
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    Timmins, Ontario, Canada
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    Default

    Quote Originally Posted by Keith Larrett View Post
    I may have the opportunity to cut out a bunch of wooden "donut" shapes. Approx. 15" in diameter with a 2" cross section diameter. It would need to be a two-sided cut, which I think I can figure out. Probably four profile cuts with a round over bit. Two per side.

    What I'm not sure of is hold down when the piece is flipped over. Using a round over bit I can't leave tabs. Any suggestions would be appreciated.
    Thinking about this for a bit this morning... while I was out shoveling after our first real snowfall of the year, and playing outside with my kids.

    I was at first thinking to use the roundover and cut both inner and outer profiles - then flip. However, the only way I could see holding down the half done ring, would be to 3D cut a negative of the ring into a piece of material, and gasket it and use vacuum to hold down the ring. Probably very difficult to get the tolerances necessaty spot on.

    Then I was thinking, it would be far better to profile either the inner, or outer edges of BOTH sides. Then create a fixture that either grips the entire outer profile, or inner (think some sort of expanding circular ring) and then profile the opposite perimeter.

    This would require more flips. But, it would be safe and positive IMO.

    SOmething like this... cut out the exterior of the circular blank, and radius the outer edge. Flip, and radius the other edge.

    Now, on a fixture that is designed to clamp around the now cut outer profile, cut the interior hole and profile, flip and profile again.

    I think if you used some of those sideways acting toggle clamps, or made a 4 piece (in quarters) fixture that would clamps tight around the ring, with some sand paper 2 sided taped to the "jaws" to grip the ring firmly, it would do fine.

    Did I make myself fairly clear?

  5. #5
    Join Date
    Jan 2004
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    Marietta GA
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    I'm with Steve on this one.
    Cut out the discs and do the roundover(s) by hand. Wayyyyy faster. Single bit operation, no flipping, and the roundovers will go much more quickly.

  6. #6
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    +1 on Steve after playing with it!
    (didn't realize moulding toolpath had so few options, and still takes a long time )
    Scott Plaisted
    Desktop/spindle/VCP 8.5**
    Maine

  7. #7
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    Elgin Illinois
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    Keith, maybe I am missing something, but why not just cut out a front half, and a back half, and then glue the two halfs together to make each donut? Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 8.5, Rhino 5

  8. #8
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    Jan 2011
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    gleason, wi 54435
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    you said a number of them so if there is enough to justify a little expense I would get a 1.0"r round over bit. Round over the 1st side to 1.0 " deep, flip into custom female vacuum fixtures, route side 2, sand and go.

  9. #9
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    Keith…
    A method I used recently involved a flip op with a radius bit. My radius cutter left a ¼” flat web 1/16” thick between the part and the scrap. I followed this up with a 1/4” endmill and left two ½” 3D tabs in the center of the part. Doing tabs in this manner left the radius cut smooth and unblemished by the tab process. This method is only feasible if it’s OK to have a narrow flat spot in the center of the two radii. In my case, I deliver the parts in the scrap matrix and the customer cleans up the tabs.
    SG
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  10. #10
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    Jan 2015
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    Thanks very much for sharing your collective knowledge. I had thought of the custom female vacuum fixture, but not having much experience with vacuum fixtures I had been leaning towards Andrews idea of an external clamping fixture. What I had completely missed was the obvious, cutting them out with a straight bit and then rounding over on the router table, suggested by Steve.

    When I first got the CNC I was thinking it would be the answer to everything. I learned in short order that there are often other tools in the workshop that are better for certain applications. It's funny how we often forget that

    Chuck, I do like your idea of cutting a front and back and then gluing them together. If there is an issue getting 8/4 stock that would be a good alternative as it could be done from 4/4 stock.

    Thanks again for all the suggestions!
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