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Thread: Sanding very tight concave surfaces

  1. #1

    Sanding very tight concave surfaces

    What do you find is the best way to finish sand very tight concave surfaces? A soft ball sander seems like it should work but the reviews I've seen for commercially made ones are not terribly enthusiastic. Have you found a method or tool you really like?

  2. #2
    Some just use folded sand paper, that works pretty well. But on some soft woods the soft grain will wear away fast and leave dips. I like to
    use a flexible backer to help make a uniform surface. The springs from broken tape measures are my favorite .

  3. #3
    Join Date
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    Quote Originally Posted by Alan Kalker View Post
    What do you find is the best way to finish sand very tight concave surfaces? A soft ball sander seems like it should work but the reviews I've seen for commercially made ones are not terribly enthusiastic. Have you found a method or tool you really like?
    I sand most concave surfaces by hand with fine paper after using curved hand scrapers to smooth. I can often start with 320, 400, or even 600 paper.
    I usually use a "soft" sanding block, sandpaper wrapped around a Magic Rub eraser. Conforms nicely to any curve.

    The question is what is the "radius" of the concavity and can you get your hand into it easily. If so, it is so simple. If tight, it's more difficult but still the best solution in my experience. I'm working on woodturnings but should apply to all types of projects.

    One advantage to using hand scrapers is unlike power sanding they will not abrade softer areas of the wood more than the harder areas. Another advantage is the clouds of dust from power sanding are avoided. In addition, it is far easier to remove small irregularities.

    Some of the surfaces I've smoothed with curved hand scrapers and fine sandpaper, sanding by hand:

    Shallow
    penta_jatoba_IMG_7636 - Copy.jpg cedar_bowl.jpg

    Deeper

    blackwood_box_IMG_8158.jpg BOC_E_IMG_7171.jpg

    Scrapers in use:
    _scrapers_IMG_7818.jpg _scrapers_IMG_7827.jpg scraper_box_IMG_20171220_113442_765.jpg

    A few of my scrapers (I have many more, some with similar and some with much different shapes):

    scrapers_favorite_IMG_7870.jpg

    I usually make the thinner scrapers from card scrapers and sharpen the same way.
    The two thick scrapers are from Stewart McDonald and are sharpened differently.


    JKJ

  4. #4
    Join Date
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    I have a bunch of variations of these, mostly for bodywork, and boats, but they come in handy for woodworking too.

    https://www.amazon.com/Motor-Guard-S...9095009&sr=8-2

  5. #5
    I should have shown this photo in my first post. I'm referring to the inset in the table top where the leg pokes through. Until now I've hand sanded the area. It is not my favorite thing to do, especially on a hard wood like Maple. I'm wondering if anyone has use a flapper type sander on a drill for that type of tight curve?
    Attached Images Attached Images

  6. #6
    Yes, they can work. Klingspor has 1"diameter flapwheels with a 1/4"shank. McMaster Carr has some smaller ones with 1/8" shanks. It can be hard to avoid rounding over the contour if you have to remove much material. An oscillating spindle is probably best if you have a small enough one, or shank-mounted small drums are available. Small flap sanders can be expensive as they dull fairly fast.
    Last edited by Kevin Jenness; 04-22-2021 at 2:25 PM.

  7. #7
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    Quote Originally Posted by Kevin Jenness View Post
    ...It can be hard to avoid rounding over the contour if you have to remove much material. ...
    That's one reason I generally prefer handheld scrapers to powered sanding - wood is smoothed without the risk of losing crisp detail. Well sharpened they work well on end grain and side grain.

  8. #8
    Alan, what is the inside radius? That is a nice detail but hard to execute cleanly.

    The pockets shown are hard to deal with and to end up with smooth transitions out of the corners no matter what tool is used. I would find scraping the end grain and through that corner difficult without leaving any scars. As always, a crisp cut requiring minimal cleanup is best. If using a handheld router I would come in from both faces with sharp alternating top and bottom bearing trim bits so as to enter from the edge and end on the side grain. A mirror image sanding block with sticky back paper used across the grain would be as good as anything to maintain the shape, followed by final sanding with the grain at the bottom of the pocket.

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