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Thread: Rings in the bottom of my bowls

  1. #1
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    Oct 2009
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    Rings in the bottom of my bowls

    When I introduced myself a few months ago, I mentioned that I planned on learning how to turn bowls this year. So I stopped by my local Woodcraft a few weeks ago and being Sunday with playoff games, the store was pretty dead. The guys behind the counter were bored so they talked me into a basic bowl turning class. Not bad: 4hrs on instruction for $65.

    So here I am a few weeks later turning some bowls and I notice that my sanding is seems to be extremely subpar. No matter what grit I use, I can't get rid of the growth rings. I thought it was the wood (Ambrosia Maple) so I switched to Mesquite. Same problem. I've gone down to 80grit and used three full sheets of paper. That's about 45 minutes of sanding. Still have the rings. If it isn't an issue with my sanding, what could it be?

    adam

  2. #2
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    Adam, I'm a bit confused about what you're calling the growth rings. Do you mean you can feel the wood grain as slightly raised ridges in the bottom of the bowl? If that's the case, what you're seeing is the result of the sandpaper taking away the softer parts of the wood (the parts between the rings) faster than it takes away the harder parts of the wood (the rings themselves). Ironically, the more you sand the wood the worse it can get. It's happened to all of us, I'd bet. Some woods are affected by this more than others.

    The only way I know to get around it is to make your cuts with the gouge and/or scraper as smooth as possible, thus reducing the amount of sanding you need to do. Also, try using a firm foam sanding pad with your sandpaper. This can help limit how much the sandpaper can dig into the softer wood. And lastly, try to sand with less pressure on the paper (and the wood). It seems counter-intuitive, but oftentimes light sanding produces better, faster results than hard sanding.
    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
    Join Date
    Nov 2008
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    Ireland
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    Hi Adam,

    Why am I thinking that you are making end grain bowls? Maybe because those are the ones that I have most difficulty sanding for exactly the reasons you say. There shouldn't really be much difference between end grain and side grain but, in my experience, there is. Vaughn has offered the best advice. I find light cuts with a scraper on it's side help a lot.
    Last edited by Brendan McAreavy; 01-28-2010 at 05:18 PM.

  4. #4
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    Nov 2008
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    Tampa & NC
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    432

    Rings in the bottom of my bowls

    How fast are you running the lathe?some will dissagree,but you will get a better finish if you run it at a low speed.I sand at about 200 RPMs on the Nova and 500 on my Ricon (slow as it will go) Also how dry is the wood ?if it is still to wet can will have that problem with some woods.I turn a lot of Ambrosia maple,but don't finish it untill it is completly dry and get a nice smooth finish.Hope this helps.

  5. #5
    Join Date
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    Catalunya
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    Although I'm no turner, sanding is a technique that is used also in flat work.
    As Vaughn has mentioned putting a harder foam pad behind the paper helps.

    If one is sanding with his bare hand behind the paper, he is going to get that raised effect on the harder growth rings. In really soft woods I avoid this by sticking the sandpaper on a piece of ply or a flat scrap, when sanding round recesses or grooves I just roll the paper on a rod.

    Then as the paper doesn't adapt to the surface only the raised points are sanded leaving the lower ones untouched until all the surface is even.

    My two cents
    Best regards,
    Toni

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  6. #6
    All the advice offered is good and factual (from my experiences)

    I have also used a sanding pad in an electric drill while the lathe is turning slowly, Working together they seem to eliminate the ridges but for the most part there will be a difference in the surface errosion with dinsity of the growth rings.

    Also soak the bottom in some finish allow to harden then sand, The toughness of the finish may harden the soft spots to sand with the same texture as the hard grain.

    A more anal method may be to get a magnifying glass and some tiny little sanding pads and very carefully sand the ridges with a more course paper than you use on the soft wood, of course you do this w/o the lathe turning (almost impossible when it is over 100 RPM DAMHIK)

    I'm sorry, couldn't help it, been one of those days....

  7. #7
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    You have gotten some good advice. I have found a sanding pad held in a angle drill running about 200 rpm works pretty well. I use a stiff pad which works pretty well.
    Bernie W.

    Retirement: That’s when you return from work one day
    and say, “Hi, Honey, I’m home – forever.”

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  8. #8
    Join Date
    Oct 2009
    Location
    Mesa, AZ
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    Thanks for all the advice. Here's a bit more info about the Mesquite. It's from a small (maybe 2ft long, 12 diameter) log that I have had in my garage for almost 3yrs now. I basically cut a slice off so I could see all the rings, hoping it would make for some interesting patterns/colors doing it that way. Just to be clear, when mounted on the lathe, the rings are visible towards the head/tailstocks.

    When I look into the bowl at its bottom, I still see the ring pattern. I cannot feel any of them. Just for grins, I broke out the micromesh and went all the way through the grits. Rings are still visible but the bowl is smooth, way smooth . I've tried using one of those right-angle drills with pads/sandpaper and still have the problem. A friend mentioned that maybe I compressed the fibers by putting to much force on the gouge.

    I'll try resanding at a lower speed. I'm running about 1100rpm (small bowl).


    Thanks for the advice.

    adam

  9. #9
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    Adam,
    Short of painting over them the rings will always be visable. There a part of the wood so you could sand until you sand through the bottom and they will still be visable. Of course if you sand through the bottom then they will dissapear. If you can't feel the rings then you've got it as good as you will.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  10. #10
    Join Date
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    Quote Originally Posted by adam baum View Post
    ...I'll try resanding at a lower speed. I'm running about 1100rpm (small bowl)...
    I think most turners would agree that's a bit too fast for sanding a bowl -- even a small one. You should see better results sanding at a slower speed.
    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

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