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Thread: Vacuum Chucking a Bowl

  1. #1
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    Vacuum Chucking a Bowl

    Brent Dowell asked about vacuum chucks, and as it just so happened, I was finishing off the bottom of a bowl tonight, so I thought I’d take a few pics of the process. In the true FW spirit, I got carried away on the pics. This is gonna take a few posts.

    As Stu mentioned in Brent’s thread, Steve Schlumpf has a great pictorial of his vacuum pump setup. I figured I’d show the rest of the process.

    My setup is a little different from Steve’s, but you’ll see some similarities in the rolling pump cart. (I built mine first. Steve improved on the idea and documented it very completely.)

    The heart of the system (aside from the vacuum pump) it this little contraption. It’s the vacuum adaptor that allows me to run the vacuum line through the headstock. It’s just a threaded hollow tube, with holes on one end (where the chuck goes) and a swivel connection on the other end where the vacuum hose connects to the lathe. (Otherwise, the hose would be twisted into a knot before you could even start working.) This one is the Holdfast adaptor from Packard’s.

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    Here’s the end that sticks out of the spindle into the base of the vacuum chuck. You can see the little holes where the air goes.

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    And here’s the end that goes into the hand wheel side of the spindle. It has a quick-connect hose fitting on the swivel fitting.

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    The cone-shaped part unscrews from the threaded tube, so you can feed the tube through the spindle from the chuck side of the headstock.

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    In this shot I’ve pushed the threaded tube through the spindle, but not yet connected the cone to the other end.

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    This is how much threaded tube sticks out past the end of the spindle. (It comes from the factory longer than needed, with instructions to cut it to size.) It’s the same kind of threaded tube used in lamps, so replacement should be easy if it’s ever necessary.

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    In this shot I’ve just started screwing the cone/swivel onto the threaded tube.

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    And here it’s cinched up tight. It only needs to be hand tight.

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    Here’s the suck-u-tron. It’s the ubiquitous 220v Gast that Surplus Center was selling for a long time. As I said earlier, Steve has a good description of how the plumbing goes together in his thread. We’ll hook it up in a minute.

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    Here’s the actual vacuum chuck. When I bought the vacuum setup, I decided to start with a factory-made chuck, just so I’d know how a good one is supposed to work. Now when I make others in the future, I’ll have something to compare them to. This one is a 6” Holdfast (again from Packard’s). I have the materials to make a few more, but so far this is the only one I’ve needed.

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    Continued in the next post...
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  2. #2
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    Part II

    Here’s the business end. The bowl is some type of hard nylon, with aluminum threads that fit the spindle. It screws on over the tip of the vacuum adaptor that's been attached to the spindle. It has a hole through the middle to allow the air to get sucked out. On the rim, there are two rubber rings, but in between them is a strip of hard nylon. I’ve found that this can bruise the finished inside of a bowl, especially with softer woods, so I often add a large “washer” made of wetsuit material, cut a bit wider than the rim of the chuck. (You’ll see the edges of it in a minute.)

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    Now for a little tangent. This gadget is not vital, but it sure is handy. The threaded end holds the scroll chuck, and the Morse taper part goes into the tailstock. It makes centering the bowl on the vacuum chuck a breeze.

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    The only downside of the adaptor in the last pic is that is does not spin. You cannot run the lathe when it’s inserted into the tailstock. So…a while back I got the adaptor on the left side of this pic. It adapts the threaded end of the live center (Powermatic’s copy of the Oneway) to the 1 1/4” x 8 tpi thread in the scroll chuck.

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    Assembled, it looks like this.

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    And here’s how it all goes together. I remove the bowl from the lathe, but keep it attached to the scroll chuck. Turn it around, stick it into the tailstock, and it’s perfectly centered and ready to go on the vacuum chuck.

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    Being able to spin the bowl while it’s mounted to the tailstock this way is handy but not critical. It just allows me to be sure everything runs right before detaching the chuck from the bowl.

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    Back to the other side of the headstock, it’s time to hook up the vacuum hose. I use a good quality quick-connect fitting. (I had a cheaper one, but it started leaking.)

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    Snaps on just like an air hose.

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    In this shot, the lathe is running at about 500 RPM. You can see the bearing retainer on the right side of the hand wheel is blurry (since it’s spinning) but the quick-connect is just sitting there. The swivel connection in the vacuum adaptor is the trick.

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    Turn on the vacuum pump, move the tailstock up into position, and the vacuum gauge shows there’s a decent seal. This is up into the “suck-start a Harley” range. You have to pull REALLY hard to get the bowl off when there’s this much vacuum. This bowl is maple…softer, more porous woods won’t seal quite as well.

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    Continued in the next post...
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  3. #3
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    Once I have the vacuum holding the bowl, I take the scroll chuck off and replace it with a live center. It’s just a bit of extra insurance. This bowl is about 14 1/2" across and 5/8” thick, so it’s pretty heavy.

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    Here’s the inside of the bowl. You can see the edge of the wetsuit washer I mentioned earlier.

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    A little spinnin’ and trimmin’…down to a small nub.

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    Instead of turning the nub away, I prefer to cut most of it off with a little flexible flush-cut saw. It’s just less likely for me to mess up.

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    A little more cleanup work with the lathe running, and it’s ready for sanding.

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    Then a few more minutes with the little Grex random orbital sander, and the bottom's finished off. All the while, the vacuum pump is running and the chuck has a tight hold on the bowl. In fact, when I was sanding the finer grits, the dust was building up and clinging to the bottom like it was wet. It was the vacuum pulling air through 5/8” of hard maple, sucking the dust onto the surface of the wood. I could barely blow the dust off with the air nozzle. It truly does suck.

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    And the result, after a quick swipe with mineral spirits.

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    It should make a nice hefty salad bowl for someone.

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    There ya have it.

    Questions and comments are welcome.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  4. #4
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    Very well done, that is just great

    Really nice looking bowl as well, I imagine someone will get years of service out of that.

    It is funny that you mention the wet feeling of the wood, I got that too when I first used the vacuum chuck, and I've learned to put "ZERO" finish on the bowl while on the vacuum chuck, as the vacuum WILL pull that finish all the way through the bowl and you will end up having to sand the inside all over again.........DAMHIKT

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

  5. #5
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    Very Nicely done Vauhgn, and a nice looking bowl to boot.

    One question, do you leave the vacuum pump running all the time while turning?

    I'm guessing so.

    Thanks for the great Tutorial!
    Programmer - An organism that turns coffee into software.
    If all your friends are exactly like you, What an un-interesting life it must be.
    "A door is what a dog is perpetually on the wrong side of" Ogden Nash


  6. #6
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    Great pic's and nicely done Vaughn.
    Bernie W.

    Retirement: Thats when you return from work one day
    and say, Hi, Honey, Im home forever.

    To succeed in life, you need three things: a wishbone, a backbone and a funnybone.

  7. #7
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    One question, do you leave the vacuum pump running all the time while turning?

    ABSOLUTELY!!!

    Think of the vacuum pump switch as the bowl launch switch. Turn off the vacuum pump while turning and launch the bowl. Instantly.

  8. #8
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    I wasn't sure if you were able to rig up a vacuum resevoir and use some sort of 'vacuum' switch, kind of like a compressor.

    I like that. The Bowl Launch switch! I guess if there's a power 'blip' while you are turning, things can get interesting fast....
    Programmer - An organism that turns coffee into software.
    If all your friends are exactly like you, What an un-interesting life it must be.
    "A door is what a dog is perpetually on the wrong side of" Ogden Nash


  9. #9
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    Vaughn,
    thans for taking the time and made
    this interesting tutorial.
    I really like this kind of post where you are
    able to learn something new.
    By the way, I have learned a lot
    here.
    Felicidades Vaughn

  10. #10
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    Although I do not have a lathe (well in fact I do but it is a hand drill powered one) I find all this post really formative and full of fantastic information, that I will probably use in the future.

    However, and excuse my ignorance, I understand that you're using a separate vacuum pump but what would a the minimum requirement in bar or psi that a pump would need to supply to have a decent hold? Obviously the more the better. But what would that minimum?
    I had a look at Steve's post and I cant find the vacuum that that pump delivers on his description of the pump.

    Apart from that it is funny to find out that the vacuum created by the chuck was sucking the wooddust from the sander. It makes a lot of sense to me as it was sucking following the direction of the grain /sap channels as if a bunch of straws it was. If it had been perpendicular to them I believe it wouldn't have happened.
    My only concern is that with that it was loosing suction power, has it happenned to you having to increase the suction pressure of the pump due to this fact or having to wax or seal the surface to provide a more airtight surface? Not on this one of course but in other more porous woods?

    Thanks for such a thorough post Vaughn, and congratulations for the bowl
    Best regards,
    Toni

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