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  1. #1
    Join Date
    Sep 2010
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    Melbourne
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    Default Correcting the bent neck of a classical guitar

    Hi all,

    I recently acquired a classical-style guitar - a Japanese model called an Abe, made by Zen-on. It cost me all of $10 from the op-shop, so not exactly a huge investment. I had to make a few small repairs, and it's turned out to be a lovely guitar - under the grime was some lovely looking timber, the binding is nicely finished, and the tone is a big step up from my previous cheapie classical. For the price, I'm very happy with it.

    But there's one slight problem: the neck is bent. There's also some bending on the soundboard around the bridge - there's a dip in front, and a rise behind. I guess someone put steel strings on it at some stage and the extra weight bent the neck and pulled up the bridge.

    Attachment 186184
    Attachment 186185

    I can probably take a couple of millimeters off the saddle, but that would still leave the action a little high for my liking (I'd guesstimate that the strings are currently about 7 or 8 mm off the frets at the 12th fret).

    I got to thinking: could I reverse some of the neck bend by clamping the guitar up for a few weeks/months with the neck being forced away from direction of the bend? Would a very light application of steam assist? Financially, this guitar doesn't owe me anything - I've already had my $10 worth of fun with it - but I don't want to totally ruin it either.

    So I ask of the collective wisdom: has anyone tried this before, and what were the results? Or does anyone know a better way to achieve a straighter neck?

    I have a not-so-lovely Terada with a similar issue, so that could well serve as the test victim before I try the Abe.

    Any advice gratefully received.

    Thanks,
    Philip.

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  3. #2
    Join Date
    Sep 2007
    Location
    Caves Beach, NSW
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    Default

    Well before you do anything, measure acurately rather than guestimate the string height from fret to underside of string at the 12th fret.
    Then measure the amount of bow in the neck by holding a string to the fret at the 1st and 12th frets and measuring the clearance at the midpoint between. Use feeler guages if you have them, estimating tends to be inaccurate.
    Bending the neck back to straight cannot be done by just clamping, it needs a controlled amount of heat applied to the fretboard to soften the glue and allow it to slip and realign relative to the neck.
    Unfortunately not a easy job for the inexperienced.

  4. #3
    Join Date
    Sep 2010
    Location
    Melbourne
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    36

    Default

    Hi Jeff, thanks for your response.

    Quote Originally Posted by jeffhigh View Post
    measure acurately rather than guestimate the string height from fret to underside of string at the 12th fret.
    Then measure the amount of bow in the neck by holding a string to the fret at the 1st and 12th frets and measuring the clearance at the midpoint between. Use feeler guages if you have them, estimating tends to be inaccurate.
    OK, height from top of 12th fret to underside of the string: 5.5mm

    I don't have any feeler gauges, so having to rely on a fine ruler, with the string held at 1st and 12th frets, the height from the top of 7th fret to underside of string is a shade under 0.5mm

    That doesn't seem (to me) to be a huge amount of bow... perhaps I need to be looking at the bridge height as well as the neck? What do you think?

    Quote Originally Posted by jeffhigh View Post
    Bending the neck back to straight cannot be done by just clamping, it needs a controlled amount of heat applied to the fretboard to soften the glue and allow it to slip and realign relative to the neck.
    Unfortunately not a easy job for the inexperienced.
    I can appreciate what you're saying, it sounds fiddly! Still, one way to acquire experience is by trying things (and quite possibly getting it wrong) and I do have another cheapie guitar I'm happy to experiment on. So if you can give me any pointers on how to go about it, I'm willing to give it a try. The questions that spring to my mind are: what temperature? For how long should it be applied? And where should it be applied? I would assume fairly evenly over the fretboard, but any words of wisdom would be appreciated.

    Cheers, Philip.

  5. #4
    Join Date
    Sep 2007
    Location
    Caves Beach, NSW
    Posts
    277

    Default

    For a classical guitar the standard 12th fret action is considered 4mm on the low E and 3mm on the high e
    To lower the 12th fret action by 2mm , you would need to lower the saddle by twice that ie 4mm.
    You probably will not be able to go that low without lowering the break angle of the string over the saddle too far. Do what you can.
    That amount of bow in the neck is just at the high end of normal, I would not do anything to it.
    It is worth checking the slots in the nut to see if they are the right depth, when you press the string down between the 2nd and 3rd frets it shoulf just clear the first fret by about the thickness of a sheet of paper.
    Good luck

  6. #5
    Join Date
    Apr 2005
    Location
    Melbourne Outer East right next to mount dande
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    1,859

    Default

    in the old days the guitars neck bow was controlled by refretting with wide tang frets
    the skill was in choosing the right thickness fret tangs to get the neck just right

    guitars never used to have truss rods up till the 40's when gibson started using them - martin followed suit and pretty soon even leo fender had to concede that the truss rod was an essential

    you can clamp and bend till the cows come home and it won't make a scrap of difference
    once you get some posiitve on that board the neck will remain stubbornly bent

    as it is a cheap giutar it is a perfect candidate for a refret
    you can buy frets with wide tangs
    you can even buy tools to crimp standard tangs out a bit
    ray c
    dunno what's more fun, buyin' the tools or usin' em'

  7. #6
    Join Date
    Sep 2007
    Location
    Caves Beach, NSW
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    A slight bow (relief ) is good to have for most guitars and more is commonly used on classical guitars due to their lower string tension and hence greater string excursion.
    The 0.4mm or so Philip is measuring is at the high end of acceplable for a classical guitar so I would leave it be

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