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Thread: Cutting a donut

  1. #11
    Join Date
    Jan 2015
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    Quote Originally Posted by steve_g View Post
    [FONT=arial][SIZE=4]
    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
    Thanks for the explanation and diagram Steve. I was writing my previous reply while you were posting.

    I couldn't visualize how to do the tabs and leave a smooth profile on the radius cut, but see how leaving the 1/16" flat can achieve this.

    I will ask if the flat would be acceptable as this is a good approach as well. Thanks!
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  2. #12
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    Jun 2013
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    Quote Originally Posted by Keith Larrett View Post
    .... 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. ....
    If you have to make many of these donuts, I would not discount the vacuum fixture(s). A flat one to machine the first side and a female half-donut mold for the other side. For larger quantities (more than 5 or 10?) it might save you a lot of time and a little material. I use that method for bowls and dishes, below is a disposable fixture for a squarish bowl. The narrow donut would need a better gasket, though.

    That said, I would probably turn the donuts on the lathe with a similar custom vacuum chuck. Even faster and you can sand and finish the surface on the lathe with minimal effort.

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  3. #13
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    Quote Originally Posted by Burkhardt View Post
    If you have to make many of these donuts, I would not discount the vacuum fixture(s). A flat one to machine the first side and a female half-donut mold for the other side. For larger quantities (more than 5 or 10?) it might save you a lot of time and a little material. I use that method for bowls and dishes, below is a disposable fixture for a squarish bowl. The narrow donut would need a better gasket, though.

    That said, I would probably turn the donuts on the lathe with a similar custom vacuum chuck. Even faster and you can sand and finish the surface on the lathe with minimal effort.
    Thanks. I will look further into the vacuum fixture. If this happens it will be more than 5 or 10.

    Actually, the prototype was turned on the lathe. The same issue was encountered, namely, hold down. That's why we were exploring making them on the CNC.
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