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Beware ! You're in Kamikazie here. Not many pro luthiers around, more often brave souls experimenting in their kitchen.

Torture for bowed neck - by François

Unbowing a neck - Harmony lutherie

Unbowing a neck - Harmony lutherie

François : I bought this H74, a nice guitar and nice case but with an exploded fretboard... I had a "New Old Stock" one so I jumped... My fretboard was intended for a H78, has block inlays so it will not be original but.. an upgrade. More about it later...

The fretboard was broken and unglued, cleanly separed from the neck. I am still wondering what made this happen. From damages on the bridge (an easy reglue) perhaps the guitar just badly fall from a stand on its face. Also there was not a lot of glue between fretboard and neck, perhaps a factory default.

Anyway, the neck itself was not damaged at all, except the clever previous owners let the strings in tension.. They were still in tension when I received the guitar... So you guess what the result was : a very bad bow in the neck.

I installed the following torture bench and after some wait (3 weeks) the neck is back to almost straight shape, ready for his new fretboard. Pictures are self-explaining. I am sure this technique could be applied to set necks, on the guitar itself ! (I will try it...)

Unbowing a neck - Harmony lutherie

Unbowing a neck - Harmony lutherie

I propose these keys to success :

  1. protect neck on every contact point with a smooth material : I use cork. You'll have to drink wine.
  2. use a rigid metallic rod. Mine is a rectangular section chromed stuff, from an old metallic desk.
  3. To distribute load, use a large wood block (and cork) where the clamp touch the neck
  4. Use trial and error to determine *where* to place the clamp. At first, apply only moderate pressure, just enough to unbow neck to perfectly straight. The neck strength is different from its widest to his narrowest width, so the optimal place for the clamp is *not* in the middle. When you find the position to have it straight on all its length, apply more pressure to bow the neck the other way. On the picture you can see the neck touch the metallic support, with a bow resulting from the thickness of cork shim at each end of the neck.
  5. Check the progress from time to time (use a rule) : if you forget it a year in the garage, you may end with a neck bowed the other way...

rlspt : cool, francois, nice work. love the desk leg straightedge. best use of junk lying around i've seen lately. kitchen kamikaze luthiery at its best.

Incidentally, i agree with your falling on its face theory to explain the fretboard popping off. too bad the idiot left the strings under tension; the neck is obviously more vulnerable with the fretboard off. the fretboard can add an amazing amount of stability. one remedy for neck bow is to install a new fretboard, slightly thicker and of a stiffer wood. especially clever luthiers introduce a curve into the new fretboard to counter the curve of the neck. i've also heard of remedying the curve of a neck by refretting the existing fretboard with new frets with a slightly thicker tang- setting the frets forces each fret slot open ever so little, lengthening the board enough to counter the neck bow..

Michael : It also works the other way around (thinner tang for a back-bowed neck). Dan Erlewine describes the technique in his book.

rjones652 : Hi Francois, would the same technique work on a twisted neck?
I have a Kay artist that has a rise on the high-E side and a drop on the low-E side.

François : I am sure it could work. The only limitation of this technique is durability, ie you can unbow/untwist, but if the neck has the bad habit to go bowed/twisted, it will bow/twist again... But with luck the process can take some time, with a perfect playability before torture is needed again...

On any guitars, the wood works in tension through the years, a certain amount of bow is created, but, more or less, it stops to a stability point. If you do a reset (unglue the neck, sand the contact joint, reglue the neck in the correct angle), the neck itself is untouched and will not bow more.

With the simple clamp technique, you ask the wood to go back to its original shape, but it will compress and bow again, even faster than the first time. If it took 30 years to have a certain bow, and you force it to unbow, it will need only, perhaps, 3 years (or months !) to bow again to the same amount...

In the case of the H74 above, the fretboard is separated, and gluing a new fretboard on a straightened neck will help a lot to maintain it straight for a longer time...

ukdenis : I was thinking about trying this technique on the old neck of my H54 without taking the fingerboard off. What does anyone think? Seems to me like I might end up with a neck I might be able to ebay - I realise there's a lot of "mights" in there!!
What does anyone think ?

Howmany : Fixing that Rocket neck is definately worth a try. I used to do repairs in a music shop years ago and we had the same type of rig as Francois is showing except that it was an electric plug-in unit that sat on the fingerboard/frets and heated up the whole thing. Not hot, not luke warm....just warm-hotish. We would clamp and the neck would be good as new the next day....maybe 2 days. Worked every time! I just checked Stewart MacDonald but didn't see one of these neck irons there....I thought I had seen one earlier....maybe I just can't find it. I suppose a person could add some heat with a lamp to Francois' rig if you were careful.

Howmany : Here is one... I found it on Aria guitars' website

Archived version of the Aria page about a neck straightener

Unbowing a neck - Harmony lutherie

Snapcase : Heeeeeeeeeyyyy !!!!! I want this !!!! Too many bowed necks around, some quite playable, some barely. I don't care how much would this thing costs. Take two guitars to the luthier to correct the neck and sure it costs more than this gear. I'll buy it.
Thanks, thanks, thanks !!!!

ukdenis : I emailed Aria in the UK about their straightener - got the reply just now. The recommended price is £410 - give or take $900 dollars. I think I am going to try something else.

Howmany : $900....that's outrageous! There's gotta be one available for under $200.....we must keep looking!

raz : $267 from lmii.org ?

Unbowing a neck - Harmony lutherie

François : Quote : "The heating element in the neck softens the glue joint between the fingerboard just enough to allow it to shift and then cool while clamped in the desired position."

This sounds like a dream. I wonder if it works for real...

raz : I've been toying with the idea of buying one for a while... while not effective for correcting bowed necks, I had the though as well that a pet electric blanket that you buy at one of those overpampered pets stores might work to help loosen fretboard glue and might be a lot cheaper.

Howmany : I wonder what would happen if you just had a rig like Francois'....a metal bar the width and length of your neck and/or fretboard, and just used a household iron on it to heat it up. It would be time consuming and you couldn't leave it unattended.....but....hmmmm.

bug music : Anyone tried this method ? No need to even heat the glue.

Unbowing a neck - Harmony lutherie

Howmany : When I used the neck heating iron in my music store days, I don't recall any discussion or thought about it softening up the glue. My boss was a French violin maker so he knew his stuff. I seem to recall it was just the idea of heating the wood so that when you bent the neck and internal rod, it would remember it's new "straightness" when it cooled down and you could then fine adjust with the truss rod. A lot of the guitars I worked on were low end flattops....Epiphone, Yamaha, Aria, Fender, etc. all from Japan, and I highly doubt they were put together with hide glue, more likely cheap white glue which I don't think you can melt. The Guilds, Gibsons, Martins, Gurians, Normans.....of course they were another story. (If an Ovation needed work, I would just send it to the local "toys for kids" charity.....in fact, I wished I could have done that as soon as they arrived from the wholesaler......what a bunch of sh!t! LOL)

François : Yes Lester, I'm sure it can work that way (heating the wood..), the "softens the glue joint between the fingerboard just enough to allow it to shift" is pure poetry, or technical blah...

Snapcase : Leaving glue appart. Heating and pressing wood to get it in-shape makes a lot of sense. Just think about rims. They're shaped by heating them. The same with archtop pressed tops and backs, they're heated and pressed to get the proper arched shape.
I think Lester's boss knew what he was doing with those bowed necks.

august 2005

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