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Thread: Small cracks on inside of bowl

  1. #1

    Small cracks on inside of bowl

    Hi Guys,

    I've rough turned a few bowls and finished some of them pretty nicely. The bowls are not that large (about 10" or 11") and I let them dry for about 5 months. After rough turning, I applied end grain sealer ONLY to the OUTSIDE of the bowl on the end grains. The bowls did not crack during drying ... however after finishing them, I've noticed a few small cracks on the end grain INSIDE the bowl (see pic). I can't see any on the outside.

    Did I not let them dry long enough? Is there something else I've done wrong during the process?

    Thanks,
    Dawson
    Attached Thumbnails Attached Thumbnails bowlcracks.jpg  

  2. #2
    Join Date
    Oct 2006
    Location
    ABQ NM
    Posts
    30,015
    How fast are you running the lathe while sanding? Those cracks looks like they could be from overheating the wood during the sanding process.
    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
    Not sure of the exact RPM, but its at it's slowest speed. I'm using small sanding pads that attach to the end of my drill to sand the bowl.

    Is it possible that my drill speed is too high? Or perhaps I am applying too much pressure on the drill when sanding?

  4. #4
    Join Date
    Dec 2006
    Location
    Goodland, Kansas
    Posts
    4,834
    Something is causing the heat. I agree with Vaughn that is what it looks like. I use low speed with 3" disc's on mine and you don't have to put much pressure at all. Let the sandpaper do the work.
    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.

  5. #5
    Thanks guys. I'll try not applying as much pressure on the drill next time and see if that helps out.

  6. #6
    Join Date
    Mar 2007
    Location
    Phoenix, AZ
    Posts
    112
    I know I've caused cracks from overheating during sanding. Some wood seems to be more prone to it than others. If you continue to have trouble after sanding with a little lighter touch I would guess these are cracks that just did not become visible until you put on the finish. I'm in a very dry climate (Phoenix) and can tell you that sometimes it seems all the tricks available to you are not enough to keep all the cracks out. If it becomes an ongoing problem I would coat your next blanks inside and out, and possibly wrap in newspaper or brown bags. You may even end up going the DNA route. Others can give you more info on that if you need it. I really hope for your sake it's just the heat build up from sanding. That would be the easiest thing to fix as it's just a minor change in technique.

    Ken

  7. #7
    Ken, you're comment about certain types of wood being easier to crack (due to heat) is interesting ... I never realized it before, but both bowls that have these types of "heat cracks" are Cherry. Perhaps that type of wood does not stand up to heat well, I'll keep trying and post some results.

  8. #8
    Join Date
    Oct 2006
    Location
    ABQ NM
    Posts
    30,015
    Dawson, as I understand it, cherry (and other fruitwoods) is more susceptible to heat cracks than many other woods. So it sounds like your assumption is correct.
    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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