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Thread: How much will final sanding take off the top?

  1. #1

    Question How much will final sanding take off the top?

    When graduating a spruce top, how much thickness should I reserve for final sanding?

    I'm building a Saga kit. I've graduated the maple back and am about to graduate the spruce top, which has about 22 grains/inch. I've measured the thickness on the inside and after my experience graduating the back I know how I'm going to approach it.

    The top is nicely rough-sanded. Most of it is fairly smooth but there is a bit of fuzz in a few places. My guess, not being an experienced woodworker, is that I'll need at least 1/100th inch for final sanding, but I might need more and I'd appreciate the voice of experience.

    Any advice? Should I consider doing "semi-final" sanding on the top first? My measurement device isn't hard on the top; I'll be setting the finish-side on a wood bump and lowering the gauge with a drill press. So I don't expect to mar it, but I won't want it finish-smooth quite yet. My measurements are good to a little better than 1/100" inch.

  2. #2
    Registered User sunburst's Avatar
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    Default Re: How much will final sanding take off the top?

    I usually measure thickness sanded to 80 grit and 120 grit, but I use measurement to get me in the ballpark on the stiffness and mass that I want and go by feel and experience from there, usually reducing the top center thickness. My final thickness measurements are recorded before the body is assembled and final sanded, so actual thicknesses might be a little thinner than what is written in my book. In other words, I don't work to specific thicknesses but instead try for a ballpark stiffness and mass to work from. I don't know how much thickness is lost to final sanding because that is done after the body is assembled and I no longer measure. Certainly the small amount of thickness lost to final sanding is unimportant to overall stiffness.
    For a beginner, carving to the published thicknesses will work fine and final sanding shouldn't make any noticeable difference.

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    Adrian Minarovic
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    Default Re: How much will final sanding take off the top?

    I've seen folks sand through 1/8" thick spruce so much depends how you sand and what grits are you using. I scrape and sand plates to 150 grit before gluing to body. I only count with minimal material removal to clean up any dirt or glue stains.
    Adrian

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    Registered User sunburst's Avatar
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    Default Re: How much will final sanding take off the top?

    Quote Originally Posted by HoGo View Post
    I've seen folks sand through 1/8" thick spruce...
    That would certainly go well beyond anything I would consider finish sanding!

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    Registered User j. condino's Avatar
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    Default Re: How much will final sanding take off the top?

    Adrian is right. I've seen some people who are delicate and very detail oriented who will literally take a week to do what I spend 15 minutes sanding. On the other end of the spectrum, I once had a student whom I said, "...sand down a couple of millimeters more and you are good." Within 15 minutes, he sanded completely through almost 1/2" thick archtop guitar top. He did the exact same thing on top #2 a few days later.....

    There is no best way, so develop a method to answer your own questions: take very detailed measurements, sand for five minutes, and measure again. You'll have a baseline and can calculate time from there. Remember that this is not unicorns and fairy dust. A systematic, methodical approach will get you the desired outcome consistently.
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    Adrian Minarovic
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    Default Re: How much will final sanding take off the top?

    I forgot to add that I often do some final graduation from outside after final assembly (I did not do much on the latest two as I worked with the same wood and already knew how it worked). But I get the surfaces pretty smooth before final assembly overall in case no thinning is needed, except near edge with platform for binding that will get cleaned after installation. I always measure thicknesses from outside before finishng so I know where the grads ended.
    Adrian

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    Default Re: How much will final sanding take off the top?

    You don't indicate how you're going to sand, but in another thread, you said you're using an orbital sander. I wouldn't use an orbital sander on spruce; 80/100 grit by hand on convex sanding blocks is fast enough.

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    Registered User Schneidly's Avatar
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    Default Re: How much will final sanding take off the top?

    Quote Originally Posted by SBJ View Post
    You don't indicate how you're going to sand, but in another thread, you said you're using an orbital sander. I wouldn't use an orbital sander on spruce; 80/100 grit by hand on convex sanding blocks is fast enough.
    Thanks for all of your insights about sanding. What are you all using for sanding blocks for sanding the tops and backs?

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    Adrian Minarovic
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    Default Re: How much will final sanding take off the top?

    Piece of 1/4" thick cork 2 x 1 1/2" approx. Handheld with a piece of sandpaper. Adjusts well to convex and concave surfaces.
    But only for the last stage with 180 and finer grits after few cycles of wetting and drying. Only scrapers before that.
    Adrian

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    Registered User sunburst's Avatar
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    Default Re: How much will final sanding take off the top?

    For sanding of tops and backs I use folded 1/4 sheets of sandpaper, fingers and thumb.

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    Registered User amowry's Avatar
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    Default Re: How much will final sanding take off the top?

    I use a random orbit sander on spruce archtops, but I turn the speed almost all the down and keep it moving constantly. It takes a bit of practice, especially around f holes. The way I sand I would say that removal of 0.01" is about right for finish sanding.

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  19. #12

    Default Re: How much will final sanding take off the top?

    I'm using the orbital sander for graduating. I'll sand by hand for finish sanding.

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