Can I save a warped back??

Discussion in 'Guitar Building' started by marco, May 17, 2015.

  1. marco

    marco New Member

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    Hi guys, first time poster on this forum.

    Just over a year ago I started to build my first acoustic from scratch, I got fairly far but unfortunately had to work abroad for a spell. I left the back plate - joined and braced - at my folks place, but on returning I found that it has warped from a nice radiused concave shape (I can't remember what radius I used) and is now convex.

    My best guess is that the heating/dryness in their house has dried out and contracted the tone wood.

    Could anyone offer any insight as to how I might be able to fix this? I'd really appreciate any advice.

    I will try to link some pictures soon if that's helpful :)

    Cheers,

    Marco
     
  2. DRF

    DRF Member

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    I'm about as far away from acoustic building as one could get so I shouldn't even comment, so until someone qualified responds I'll throw this out there for ham fisted consideration/entertainment. Take it in the shower with you, no not the shower itself, it may take 1, 2, or 3 times but a good ole steaming might do the trick. Then,"paint the back with oil, boiled linseed, Tung, that sort of thing.

    It worked on a warped neck I had for a project, but I've yet to see if it will hold, I suspect it may not...
     
  3. otterhound

    otterhound New Member

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    Don't waste your time . Hang it on your wall as a reminder .
    Chalk it up to a learning moment and join another back set .
    Don't do this until you are ready to use it .
    Assembled bodies can sit for long periods as long as they are in a stable environment that is not too dry .
     
  4. Duplex Dave

    Duplex Dave Active Member

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    You can remove the braces with some flush cut end nippers. Switch to a chisel as you get closer to the back and finish off the removal with a cabinet scraper.
    I have seen this happen when the braces are not glued on with the correct grain orientation. Specifically if the brace grain is not perpendicular to the to the back.
    don't ask me how I've come across this :)
    Re-brace the back with new radiused braces. You should probably try to re-humidify the back plate back to around %45 if possible. If it did not crack during the transformation it should be good to re-use. (even if it did crack that can also be repaired)
     
  5. marco

    marco New Member

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    Hi everyone, thanks for the input!

    I'm sure the best thing to do would be to start again! But unfortunately I don't have my own workshop yet so it would be a giant pain! I'm keen to get the maximum learning out of this guitar so even if it's not perfect, I'll get it on the next one

    Dave, I just thought of removing the braces yesterday! Not sure why it didn't cross my mind sooner but I was pleased to see your comment... Luckily the plate isn't split, and you are right, the grain is perhaps 5 or so degrees from vertical on each side...

    I should probably invest in a humidifier. This has taught me an important lesson!

    Edit: I've attached some pictures here: http://imgur.com/a/ZkHG2
     
    Last edited: May 19, 2015
  6. Duplex Dave

    Duplex Dave Active Member

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    Thanks for the pics, that's a nice back I would certainly try to save it.
    Grind, chop, cut, shear then scrape those braces off however best you can.
    Don't need a shop it's all hand work.
    I bet you could press it pretty flat by spraying some water on it and using a clothes iron on medium temp. Re-hydrate it then make some new braces.
    If you already have matching sides it would be tough to match a back like that.
     
    Last edited: May 20, 2015
  7. Murkar

    Murkar Well-Known Member

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    I too am far from an acoustic builder and shouldn't comment....but unless it's warped badly you should be able to re-brace it like Dave suggested. That being said however, be careful to double check that the joint is still fine and that none of the warp is retained after re-bracing. As sad as it is to throw away nice wood, it's worse to build flaws into a guitar from the get-go that will be with it for life.
     
  8. otterhound

    otterhound New Member

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    Unless you are using hide glue , you will need to remove the residual glue down to bare wood .
    Hot glue will melt/bond to itself . Most glues will not .
     
  9. Duplex Dave

    Duplex Dave Active Member

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    The Hound Man speaks the truth, remove all the original glue unless it is protein based animal glue. (fish or hide)
     
  10. Jim_E

    Jim_E Active Member

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    You have nothing to lose by trying the simplest and most effective method, wet the concave side repeatedly so it swells on that side and torques that back into shape, I've done it more than once and it works, just takes time and repeated applications.
     
  11. marco

    marco New Member

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    Thanks for the suggestions! I've removed the braces now and the back plate seems fine, storing my materials in a much more controlled workshop now so they should keep much better. Ive remade and radiused some braces but I'm going to avoid making up the back until I'm ready to glue it on, (learned my lesson) I'll be sure to post a picture when it's all made up.

    Thanks again
     
    Last edited: Jun 16, 2015
    Duplex Dave likes this.
  12. marco

    marco New Member

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    And thanks for the tip about the glue otter hound. I actually used epoxy, as the walnut is oily and that is what I used to joint the back plate.

    What glues do you prefer to use when joining spruce to oily woods?
     
  13. Duplex Dave

    Duplex Dave Active Member

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    Excellent news, thanks for the update.
    You can use wood or hide glue with confidence with walnut.
     
  14. fmorelli

    fmorelli New Member

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    Okay, first you are not the only guy that this happened to, don't feel bad. As a matter of experience (I've been there), I NEVER brace a back without installing the sides, or keeping the braced back in a radius dish weighed down with lead bags. They will likely warp. As has been mentioned, remove the braces. A brace chisel will help. I assume wood glue, so remove, scrape and hot water on a rag (not soaking wet) will allow you to wipe glue off if Titebond.

    Good luck,

    Filippo
     

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