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Thread: Warped back

  1. #1
    Join Date
    Jul 2019
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    ............
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    Last edited by Dougbias; 10-02-2019 at 01:23 PM. Reason: Spellcheck

  2. #2
    Join Date
    Aug 2018
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    Australia.
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    It's a bit difficult for me to assess the extent of the concaving from the photos. If it is an old build, and your climate is dry, rehydration might help.
    With a new build it is likely that the relative moisture content of the back wood and brace wood was significantly different on glue up. When this happens the cross-grain shrinkage of the back wood pulls the braces into an arc.
    The last time I had one like that, nothing helped: It was back off, chisel off the braces, reduce back and new brace material to 40% RH and reglue. This is relatively simple when the instrument is not bound.
    I hope rehydration is the answer in your case.
    Wait for other opinions before you try anything, others might have had more remedial successes than I have.

  3. #3

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    How does it sound? I mistakenly sanded too much wood from the sides at the waist on a recent build, leaving a back that was convex side to side but concave top to bottom. The uke has great sound, long sustain, and great overtones!

    If it sounds good, don't fix it, would be my advice.

  4. #4

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    Quote Originally Posted by Dougbias View Post
    Thanks for the response. Unfortunately, this uke didn’t have the sound that I hoped for.
    Considering lamination to fix.
    I am not sure what you mean by this.- "Considering lamination to fix."

    Also, how much did you pay for the uke? Is it worth the trouble? Sometimes worth it to start fresh... Just thinking...

  5. #5

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    Oh, I just finished reading your other post and hadn't put the 2 together.

    I am also dealing with how to build with a compound back, but personal preference is not to use laminates. It feels like cheating somehow. ;-}

    It seems that we have both stumbled on the ability to do this, but we also both ended up with warped backs in the process.

    My focus is now on how to control the plane of the back (and the front for that matter) when gluing up so as to avoid the warp.

    How thick are your backs? Mine are a bit over 1.5mm and have no problem taking the compound curve during glue up. I just need to stabilize the rest of the uke when doing it.

    Oh yes, I believe in back braces, at least for how I am building them. Yours may be different, though.

    Good luck!

  6. #6
    Join Date
    Jul 2019
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    16

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    Thanks for the reply. I haven’t gotten as far as you yet on building my first laminated back. Still creeping up on it building domes and dishes. The way I’m planning it is to build a graduated template using a 10, radius dish to form the outer most dome of a 10’ radius then graduating the inside of the template to 12’ and then to 15 using a 15’ radius dome for mating the finished back to the sides which will have a 15’ radius using a 15’ dish. I’m most likely overthinking the whole thing though but, if you know an easier method please do share! Thanks for sharing.

    Note: the whole reason why I’m pursuing the is because I have recently move to the desert and have run into the problem of warped backs on a couple of my ukes and, I don’t want to build anymore without addressing this issue. Hence, laminating the backs.
    Last edited by Dougbias; 08-03-2019 at 07:01 PM.

  7. #7
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    Jul 2019
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    After re-reading your post I am under the impression that you are building arch backs with solid wood and not laminating . Do I have this right? Can you post some pics? I wouldn’t mind trying it out as well. Thanks for any reply.
    Last edited by Dougbias; 08-01-2019 at 06:39 PM.

  8. #8

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    Quote Originally Posted by Dougbias View Post
    After re-reading your post I am under the impression that you are building arch backs with solid wood and not laminating . Do I have this right? Can you post some pics? I wouldn’t mind trying it out as well. Thanks for any reply.
    Not sure you can see it clearly but here I am gluing the braces to the back. The braces have a radius of 4'. As you can see, it is a simple matter to get the solid back to conform to the curve.IMG_20190421_131043.jpgIMG_20190424_083035.jpg

    Here I am gluing the back to the ribs (sides). Once the ribs are leveled, they also need to be sanded to the same curve as the back, side to side. Take a 2x4, cut and smooth the curve along the length, glue on 120 sandpaper and use that to bevel the ribs by sanding across the width of the ribs. Just don't get too aggressive with the sanding - or at least keep it even. In the next uke I made, I took too much off at the waist and now the back is convex top to bottom! Still sounds great, though... Maybe it is a feature?

    Actually, this mistake also showed me that a compound arch can be done with solid wood and no steaming or other processes to bend the wood. I think the key here is the thickness of the back, and maybe the species of wood. This back is Honduran Mahogany and is maybe 1.5-1.6mm or so thick.IMG_20190424_083035.jpg

  9. #9
    Join Date
    Dec 2011
    Location
    Grand Junction, Colorado
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    2,738

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    You can't fix it- well you can, but its all too much work and its better to just move on the the next one and learn from this one.

    For the next one, make sure you
    1- Radius the sides in a radius dish. 15' for back is normal.
    2- Use a radius dish to radius the back braces and glue the back braces to the back in the radius dish.
    3- Make sure everything is humidified correctly. If the back or the braces aren't humidified then you get these problems.
    4- Also using non quarters woods can lead to things like this.

  10. #10

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    Quote Originally Posted by Beau Hannam Ukuleles View Post
    You can't fix it- well you can, but its all too much work and its better to just move on the the next one and learn from this one.

    For the next one, make sure you

    3- Make sure everything is humidified correctly. If the back or the braces aren't humidified then you get these problems.
    Humidified? What do you mean? I know what the word means, but how do you do this? I would think that everything at a stable humidity would be what you want. No? Thanks!

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