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Thread: Vacuum Chuck ?

  1. #1
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    Vacuum Chuck ?

    OK,
    Stu's recent post of his Ginko bowl has me scratching my head.

    I'm a Long way from needing one, but I sure would like to know How a vacuum chuck works. Obviously you apply vacuum to the plate and the workpiece is held on by the vacuum, there are vacuum router pads which allow clamp-less routing, but that I know of they have a constant source of vacuum. How the heck do you apply and keep vacuum on a bowl that is spinning at several hundred to several thousand RPM?
    Last edited by Ned Bulken; 10-29-2007 at 06:42 PM. Reason: spellingk correciton.
    -Ned

  2. #2
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    Quote Originally Posted by Ned Bulken View Post
    ................. How the heck do you apply and keep vacuum on a bowl that is spinning at several hundred to several thousand RPM?
    Ah.......... carefully............

    basically the headstock in "most" lathes are drilled through for a knock out bar, to get things like your drive center out, so that becomes the pipe that the vacuum travels to the plate or vacuum chuck. The hose from the vacuum pump to this tube is usually attached via a bearing that fits into the handwheel on the lathe, there is a pipe or nipple in the middle of the bearing, this is where the hose attaches, the bearing spins, the nipple does not. Make sense yet

    Cheers!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  3. #3
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    forgot about the pipe through the headstock. Gotcha.

    as for 'carefully' I take it that you can launch the workpiece if too much force is applied?

    exciting things to learn and look forward to.
    -Ned

  4. #4
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  5. #5
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    Actually with my set up, I'm more worried about collapsing the bottom of the bowl, I think they call this "Funneling" it........

    Seriously, I know that the vacuum chuck is not as secure as say my Titan chuck with them spigot jaws on it, but there is a LOT of vacuum on the bowl.

    Surface area of a sphere....
    surface area = 4pr2

    So if the bowl is a perfect sphere (and I know it is NOT) and 8" in diameter 4x3.14x4squared = 50.265 (about) so half of that for the half bowl is about 25 square inches of surface area, so if I'm pulling 20" of mercury........ ah.......

    Dunno, would that be 20 x 25 500 pounds...?

    Well, all I know is that it would take a REALLY huge catch to remove a bowl from my chuck, and as I'm just finishing off the bottom of the bowl, I don't think I have much too worry about........... unless I make the bottom to thin, thus "Funneling" it...........

    Cheers!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  6. #6
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    I have gotten them a little too thin and when that happens you know it. It sucks the bottom right through to the filter.
    Randy,

    Maker of Fine Lathe Tools & Accessories.

  7. #7
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    Hey Ned, just wanted to show you, and everyone else, the neat factor on these vacuum chucks...........

    Click image for larger version. 

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    That is the little hat from one of my snowmen, I wanted to sand the underside of the hat a bit, and thought........"hey........ I got a vacuum chuck......"

    and the next two pics, are a piece of hardwood, not light, is also held on the hat by vacuum, the wood that hat is made from is Hard Maple, not exactly porous wood, but there is enough vacuum there, through the wood, to hold that piece of wood on the hat, no rubber seal either.

    LOVE this vacuum chuck!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  8. #8
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    Interesting vacuum face plate there, Stu. Would you tell us more about it?

  9. #9
    Stu

    If I recall correctly, you have a dedicated pump for that chuck, would a vacuum cleaner work? (maybe not as well?)

    Jay

  10. #10
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    Sure Carol, it is just a piece of MDF, I think it is 21mm thick, with a thin piece, maybe 4mm, of semi soft foam on the face. I'm going to replace the semi soft foam with something a bit harder, this stuff is too soft.

    Works like a charm, as you can see

    I'd like to make some other chucks too, some bell shaped ones etc, but for now, this works well.

    Cheers!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

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