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Thread: arching and body forms

  1. #1
    Join Date
    Aug 2018
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    177

    Default arching and body forms

    I'm in the early stages of a pair of uke projects, a steel string baritone and a tenor. For the baritone body, I'm going to use a 25 foot top arch and 15 foot back arch. For the tenor, the top will be flat and the back will be 15 foot. I'll be building both on open boards without molds, using the same method StewMac recommends for their uke kits. It worked fine for me when I built the StewMac tenor kit last year.

    I've used my LMI brace sander as a template to craft a cylindrical building form for gluing back braces. I'm going to do the same for gluing the top braces, as well as sanding implements for shaping the rims. I will not be using radius dishes. I'm using Campiano's and Natelson's guitar building book as a reference. Anyone in the crowd have any tips, pointers, or warnings? I'm most concerned about tapering the backs, because that is where I messed up on my last uke project.

  2. #2
    Join Date
    Sep 2015
    Location
    Stockport, Cheshire.
    Posts
    390

    Default

    Not sure why you're not using a radius dish. I think you might find it very useful. A 15ft dish, which you can make yourself, can be used for both ukes and guitars and used time again. It will be a lot easier for shaping the back, and may reduce any concerns you have. Precut the taper prior to bending and then even things out once the blocks and kerfing is in place. The tops can be radiussed by the braces as you've mentioned.

  3. #3
    Join Date
    Dec 2011
    Location
    Grand Junction, Colorado
    Posts
    2,738

    Default

    It is too difficult to describe how to radius the sides to fit a 15' radiused back without using a radius dish.
    I used to do it and teach how to do it by hand but i can't describe it in words.
    As it seems you are making a few a year, best to spend the $90 ad get a radius dish.

    Don't bother making your own. Total PITA

  4. #4
    Join Date
    Mar 2009
    Location
    Hudson, MA
    Posts
    1,546

    Default

    Ditto on using a dish to make life easy.
    But if you really want to....its just arc height calculations. Look here: https://www.handymath.com/cgi-bin/ar...i?submit=Entry

    Let's say your body is 12" wide max and the waist is 6" min. (Change for your actual measurements of course) You have to cut the sides down from the waist to accommodate the arc as it gets wider.
    1 Set the waist as zero. A 15' radius and 0.5' width gives 0.00208' or 0.024" arc height.
    2 At the widest part: 15' radius and 1' width gives 0.00834' or 0.1" arc height.
    3 Now subtract your waist calculation to get 0.076" height difference between the waist and widest part of the body.
    4 Mark a point at the widest part 0.076" down the side.
    Repeat steps 2-4 a few more times at other body widths and connect the dots to make a smooth curve. Carve or sand down to the curve

  5. #5
    Join Date
    Aug 2018
    Posts
    177

    Default

    Thanks for the replies. Something to think about.

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