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How To: DIY Radiused Sanding Block

Discussion in 'Luthier's Corner' started by tZer, Sep 18, 2010.

  1. DIY Radiused Sanding Block
    3 5/8" x 15" x 3/4" block w/ 9.5" radius


    Take 1 appropriately sized, squared block of wood. Mine came from a scrap of a neck blank after profiling 3 5/8" w by 15" long by 3/4" thick.

    Square it, plane it, and mark it with an arc on one end.

    Set your router table fence and center on the center line of the block.
    I used a 1/16" square bit and gradually routed a channel down the dead center up to the peak of the arc.

    Turn the blank around and do it again from the other end.
    The first time that is irrelevant, but in subsequent runs that's what give you a symmetrical arc.

    Nudge the fence in slightly (about 1/2 a bit width) * - drop the bit a bit to match the arc and run it through up to the arc both directions.

    As you nudge and drop, the arc gets carved.

    * Thanks to beej for pointing out that I omitted some critical stuff...

    Once you rout the center channel, dropping the bit to follow the curve while nudging the fence in small increments to carve shave the channel outward lets you rough out an arc.

    Lather, rinse, repeat.

    Clean up the stair stepping with a curved scraper. It goes pretty quickly too.

    It goes faster than it sounds but taking your time is a good thing and remember, the smaller the increment, the smaller the stair-stepping.

    I use 3M spray adhesive to stick on sandpaper. Works like a charm!


  2. Beej


    Feb 10, 2007
    Vancouver Island
    I don't follow. How do you get the smooth arc? What are the minute steps?

  3. [Edit] I edited the post above to include the omitted details - let me know if it is still not clear[/edit]
  4. SDB Guitars

    SDB Guitars Commercial User

    Jul 2, 2007
    Coeur d'Alene, ID
    Shawn Ball - Owner, SDB Guitars
    Some people may have difficulty sourcing a 1/16" router bit. I found one at my local specialty tool store (*not* at Lowe's or Home Depot), and it is pretty shallow, allowing no more than about 3/16" - 1/4" depth of cut.

    Also, and this is speaking directly from experience :eek:, 1/16" bits break SUPER easy, so wear eye protection, use of softer woods would be advised, and taking your time, also... :D

  5. Yes - yes - yes - slow and steady - and I worked very gradually. It wasn't hard and yes - you can definitely use much softer wood - and definitely wear protection!!!

    All very good suggestions. But you get the concept. It wasn't extraordinary - didn't strain the limits of machine and man ;-) Very doable and very solid results - especially when you consider how useful these are and how long you'll be able to use 'em.
  6. Droot


    Dec 29, 2006
    Not to throw water on your parade, but I find that attaching the rotor to an arc frame and swinging it side to side works well and would appear to produce the same results with less breakage issues.
    Just my two cents,
  7. SDB Guitars

    SDB Guitars Commercial User

    Jul 2, 2007
    Coeur d'Alene, ID
    Shawn Ball - Owner, SDB Guitars
    In all honesty, I think tZer's method us more accessible to the average shop user... I, for example, would not want ti try to construct a swinging carriage for my router. Just the thought of that scares the daylights out of me. :ninja:
  8. Big B.

    Big B.

    Dec 31, 2007
    Austin, TX
    It may help if you use a bigger bit to remove the bulk of the material and then move to the 1/16th bit for the final passes. More time consuming but a lot less wear and tear on your bits.
  9. Droot


    Dec 29, 2006
    I think most people make far more of this method then it really entails. Without hijacking the thread, consider this picture from a first build.


    although it is slapped together in about 5 min, this "rig" is very simple to build and makes any arc needed. Just a couple of small boards and a table to swing across. The 2x4 sticking up is the sanding block.
    Later, Droot
  10. That'll do it too, for sure.

    I've seen this approach before and considered it but I didn't have a table large enough to accommodate. I have a very small shop with even a smaller space to operate.

    But This is definitely equally effective - if not more so. I suppose as long as you end up with a radiused sanding block it's all good, right?
  11. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

    Mar 3, 2021

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