Finishing Bowl Bottoms

Discussion in 'Tutorials and Tips' started by John Chianelli, Jan 28, 2009.

  1. Steve Worcester

    Steve Worcester Admin Emeritus

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    Maybe we should start from the beginning, and as an example, here is how I personally turn it the second time.

    I start with a vacuum chuck, but no vacuum, but simply putting the bowl opening over the chuck and the rubber helps spin the uneven inside by friction. The tenon is held in place with a live center. I first true up the top (rim) so that I know where the curve will "exit" the bowls sides. Then I true up the tenon so that I have a plane that is true if I have a bobble (catch) and need to realign the bowl. Then I proceed to turn the sides. Starting at where the bottom of the curve would be on the bowl and at first an unsupported bevel, since the tailstock engagement won't allow it. Then as I proceed up the sides I can rib the bevel. It will take multiple passes to cut supported and clean all the way through the curve up to the rim, once that is clean and true, I sand the outside, Then I can reverse it, and cut the inside, all the way through as you usually will finishing with sanding . After that, I reverse it again on the same vacuum chuck (with vacuum or without vacuum but supported by a live center) to cut off the tenon and cleaning and decorate the bottom, and finally sanding the bottom.

    So, if you have followed this far, you see I don't use colejaws. You don't have to have a vacuum, but it will make the last step easier, and allow you access to cut all the way across without tailstock and live centers getting in the way.
     
  2. odie

    odie

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    Howdy John.......

    I think you're "getting it" or "seeing the light" here! A woodturner is best off to avoid needing to re-turn, or re-sand the side of a bowl, once it's re-chucked in the Mega Jumbo Jaws......that's where all the trouble starts, and you could very well end up losing the bowl altogether, or having a major "fix-it" to do! :eek: Any surface that's intended to be finished on one chucking, is usually asking for a disaster if you mess with it on a subsequent chucking. If you have to lose a tiny bit of "real estate" (as you call it), well, so be it......much better than gambling on the outcome.

    I started out on a Nova chuck with the Cole jaws.....and have graduated to the Stronghold chuck with Mega Jumbo Jaws about 15yrs ago. After about a decade of non-use, I ended up selling the Nova chuck and Cole jaws several years ago......(Nothing wrong with the Nova chuck, or the Cole jaws, it's just that the Stronghold and MJ Jaws do exactly the same thing, plus have a larger capacity.) As far as I'm concerned, these big jaws with the rubber bumpers are a fantastic invention that I couldn't live without!

    You will find most bowls have a degree of warp, after it's reverse chucked. This will become more obvious when you see that very few bowls will set perfectly flat on the Jumbo Jaws, when viewed from the side as you are chucking up.

    One thing to remember: The smaller the diameter your foot is, the less any warping will have any effect on it.

    Even if you do have some warping, it's very easy to true the very bottom up while it's on the Jumbo Jaws.......just use a very fine, and delicate scraping cut, and/or a 2" sanding disc, also held very delicately against the base portion of the foot that contacts the surface the finished bowl rests on. (At this point, you should NEVER have to re-do anything on the sides of the bowl.)

    John, I checked out your web site......Most of the bowls I saw have, or appear to have fairly thick sides. Secondary warping of pre-seasoned bowls should be less with those than a thinner wall would have......but, then again, each and every piece of wood seems to have it's own individuality, and it's hard to second-guess what they all will do without having a crystal ball! ;) (Every time I attempt to make hard-fast rules about something involving woodturning......I usually end up eating crow!)

    You have a very nice sense of design.......simple and clean! I like your style.

    otis of cologne
     

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    Last edited: Feb 3, 2009
  3. John Chianelli

    John Chianelli

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    Thanks for the input Steve. Like pottery, there are so many different ways to accomplish a task. I appreciate reading forum members inputs as it all feeds a hopefully successful solution. The more I read the more I like the idea of vacuum chucking and using the tail stock for added support. I have some good ideas from you folks to to try several new approaches to this problem. I could not have asked for better input from everyone and am extremely grateful for the responses received on my first topic.....
     
  4. John Chianelli

    John Chianelli

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    Thanks for the extensive input Odie. It all make sense what everyone is writing here. And...thanks for taking the time to checkout my website as well. I can see why you like my sense of style after vising your photo albums. I like your forms and the attention to rim detail. The rim is one variable that can really change a piece. Rims really take more creativity and are worth the added investment of time and trial. It is all in the details. Years of pottery work gave me a great sense of form going into wood turning. Carving a form vs. coaxing a form are two entirely different animals though...
     
  5. Steve Worcester

    Steve Worcester Admin Emeritus

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    Basically, what I described is what Wyatt was talking about, I ust don't always read everyones posts.:eek:
     
  6. Wyatt Holm

    Wyatt Holm

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    Steve,
    I have used my vacuum chuck as a tension drive like you said. There is also one other way I learned. I don't use it very often but it does work, and that is a jamb chuck. Very simple to make, just a piece of mdf, or wood that you place in your chuck or faceplate. Then you cut it quite similar as you would for the lid of a box. If you get it just right it will hold your piece snug enough to finish the bottom quite well. I prefer vacuum chuck, but the knowledge of how to do a jamb chuck is good to know. I know some people think that what I call a tension drive is a jamb chuck, I am not referring to a tension drive in this post.
     
  7. Malcolm Smith

    Malcolm Smith

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    This seems pretty well covered. Reading through all the posts, the only thing that comes to mind as being less than covered is the use of the tail stock. A question needs to be asked. Is it well lined up with the headstock? On some lathes this is the case and with others, it is not the case. Oneway lathes arrive with a certificate stating that they meet correctly. They are heavy lathes that do not have rotating heads. The other lathe that I had, even if one alligned them, the head stock and the tail stock, they wouldn't remain alligned.

    One can mount a cone of wood with a small flat face on a tailstock which can then apply some pressure against the turning. I often do this if the position of the base of the bowl is shifted from where it was when the regular tail stock was first applied.

    Malcolm Smith
     
  8. Ronald Canale

    Ronald Canale

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    Bowl Bottom Finishing

    When you remount your bowl on Cole Jaws and reverse turn/finish the bottom, the bowl will always be slightly off center. I notice this when I cut my bowls off of the base plate and remount it through the opening to my Cole Jaws to finish the bottom. Any time you do remount a turned object this way, it will never be centered EXACTLY the same and you will always be off center if ever so slightly. The good part is that when you sand and finish the bottom, no one will ever notice it in the finished bowl. Personally, I wouldn't worry about it. ;)

    Ron Canale
     
    Last edited: May 28, 2013
  9. john lucas

    john lucas

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    I didn't read all of the replies so I apologize if this covers them. I did an article for our club a bunch of years ago on Methods and Jigs for Reverse turning bowls. You might find a good way to help you out.
    http://www.cumberlandwoodturners.com/htm/tips.htm
     

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