Straightening neck of vintage Gibson J50 with large amount of upbow

[Andrew Hann]

Hi,

I have acquired a 1955 Gibson J50 which was in an unplayable state. It's not original, in that the top has been refinished and the bridge replaced at some point in the past. The neck had some 25/1000th of relief with the truss rod already tight - the truss rod nut had compressed the wood at the headstock end leaving a fair amount of thread showing. So someone in the past maxed the truss rod out in an attempt to get the neck straight, without success. A nut and saddle were installed very poorly ( they were far too high) which made the guitar unplayable.

I tried the trick of looensing the truss rod, lubricating the thread, and making a couple of spacers to fit over the rod in the truss rod pocket. Then clamping the neck into a backbow before tightening the truss rod again. However, even tightening the nut again as far as I dare, there is still around 13/1000th of relief.

The frets ( not original, but original spec) are in good condition save for one or two which are not fully seated causing a couple of buzz spots. I lowered the nut and saddle so the guitar plays reasonably at this stage, albeit with a fair amount of relief. 

I'm thinking the only option for getting a straight neck is to remove all the frets, get the neck as straight as possible (in neck jig) and sand the board flat, taking off as little wood as possible, then re-fretting but using some fret compression to pull the neck out of it's upbow.

I'm not sure about heating the neck as a method - I get the feeling that this is a stubborn neck that may not respond to this treatment- but I don't know as I've not heated a neck before.

I'm a fairly recently trained luthier - done a number of fret jobs on new(er) guitars - but not come across such a tough neck bow problem, and its a vintage guitar ( albeit not all original) with the potential to sound and play really well.

I wondered if anyone has had a similar problem, worked on old Gibsons like this, and could let me have their views on my proposed course of action.

Many thanks! Andy

[Roger Häggström]

The heat from the iron will shrink the fretboard, in worst case leaving a sharp edge between the neck itself and the fretboard. Saturating the fretboard with fat oil will prohibit most if not all of that shrinkage.

Yes, the neck will move a bit after the heating. Hanging the guitar tuned up with a small weight on the endpin will speed up the process. Using patience I would have the guitar tuned up for a week before the last crowning. Glue plays a part in the straightening of the neck, but with enough heat the wood itself will "melt" between the fibers and "freeze" in the new position. The warmer you get the neck, the better the new shape will hold. The drawback with too much heat is the fretboard shrinkage, the melting of celluloid and lacquer and even darkening of the fretboard wood.

You will get the best result combining the heat treatment with a complete refret. You can sand the fretboard straight and also use compression from the frets if needed. "Hanging" the guitar tuned can be made with loose frets tapped in without glue before sanding the fretboard and doing the final refret.

[Andrew Hann]

Thanks for this Roger. Your detailed input is much appreciated. It may be a while before I get to this job as I have other stuff on but I shall let you know how it goes.

Best 

Andy

[Roger Häggström]

Hope it works out for you!

Did a Google search for some more info about the temperatures. 100 degrees C will work but the heating time is long, the recommended temperature to bend dry wood effectively is around 160 degrees C. The "cotton" setting on an iron is about 200 degrees C, the "wool" setting with around 150 degrees C is probably the one to use (celluloid inlays removed).

Check out this thread.

[Kerry Krishna]

Andrew, as I remember ( maybe John will step in here and comment) he just said it would have to be repeated. And it did. All of them, over and over. Folks who do not know how to do this, also think no fretwork will be needed, It certainly was not my experience on any of the guitars I did. 

[Andrew Hann]

Hi Kerry. Ok, many thanks for sharing your experience. I'll let you know how it goes when I get round to this job.

Cheers Andy

[Roger Häggström]

The biggest effect comes with the first heat treatment. For every consecutive heat treatment, the wood is more resistant to bending. So, it's best to get it more or less right the first time.

[Andrew Hann]

Noted, cheers Roger

[Walter W Wright]

have not tried the clothes iron+aluminum bar method, but i've had pretty good luck over the past few years using heat lamps from the hardware store over a neck clamped into the desired curve (clamped well past the desired curve actually).

i suppose they transfer heat more slowly than the bar, but that might be a good thing. i just cover the individual fretboard inlays with bits of reflective foil on top of little pieces of cardboard, and spend the better part of a day "baking" the neck while moving my two heat lamps (in desk lamp fixtures) over different spots along the neck with the goal of even heating without getting too close or too hot in one spot and shrinking the wood or damaging the inlays.

i'll leave it clamped up to cool overnight and pull it to check the next day, so far it almost always comes out changed in the direction i was trying to get it to go. (sometimes even too far!)

i've even had good luck fixing the dreaded "ski ramp neck kink" where an electric instrument neck folds up right at the transition from free to "bound" at the body.

as for what's happening, i don't think it's any kind of glue joint "slipping", that just doesn't seem right; plus i've had success with one piece maple fender necks (where the finish was already mostly gone fortunately, not sure how i could make this work on a fully finished glossy maple neck). i think the wood itself becomes "plastic" with sufficient heat and stays put once bent; that's how acoustic sides are made after all, right?

the light bulb went on for me while watching one of those silly discovery channel "weapons" shows, the one where a machinist guy uses modern methods to improve ancient weapons (crossbows in a machine shop, that kind of thing) while the other expert makes them the old way. the "old ways" guy was making spears out in the woods by cutting down twisty saplings, stripping them, heating them on a fire and then bending them straight. it was surprisingly easy to get the wood to bend and stay bent with heat.

[Andrew Hann]

Hi Walter,

I've seen a video of Dan Erlewine using a heat lamp as you describe. This method also has an advantage in being able to see what you're doing with the neck. I'm not sure what you call the heat lamp - or where I can buy one. I'm in the UK, don't think we have such a thing in general hardware stores here. Do you have any other info on the heat lamp used? Cheers 

Andy

[Walter W Wright]

a quick googling gave me this?

https://www.thelightbulb.co.uk/light-bulbs/infrared-heat

mine are i think 125w, as more than that would probably be too much for the cheap desk lamp fixtures i put them in. they're also the kind that put out bright light along with the heat, which is kind of annoying actually. i might try replacing them with the kind that just put out the infrared.

[Andrew Hann]

Apologies for delay in responding Walter. Thanks! I was kind of looking at infrared but wasn't sure what to go for - I've seen this sort of lamp advertised - on a floor mounted angle poise arrangement used by physio/ therapists which looks handy as you can move and direct the heat source easily - like the attached...275W!

https://www.ebay.co.uk/itm/FoxHunter-Infrared-Floor-Stand-Heat-Lamp...

[Allan Bacon]

Sounds like a fret board removal and a neck planning is in your future.