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Straightening neck of vintage Gibson J50 with large amount of upbow

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

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Haven't worked on an old Gibson neck, but a plethora of other old necks. Heating and bending will work. I'm sure there are good instruction on the method to find on the net, but here is the way I do it.

Loosen the truss rod and saturate the fretboard with a fat "teak oil" to keep the shrinkage of the fretboard to a minimum. I also recommend putting some plastic wrap on the caul under the neck. The lacquer in contact with the caul may get soft or sticky by the heat.

I use a flat piece of aluminum the size of the fretboard on top of the frets and one or two small traveling irons for the heat, a caul shaped for the neck with a soft material in contact with the neck (like cork) placed where the neck is bent the most and two strong clamps at the top and bottom of the neck. The guitar is put on a sturdy table, the caul on top of the table and the clamps fastened under it. The irons can be clamped too with small clamps to keep them in place. The temperature of the irons should be pretty warm but not maxed out. Overdo the back bend a little, the neck will flex back when done. I make the negative neck relief with the clamps about the same as the bend in the neck before bending it back, maby a little bit more. Heat for about 15-20 minutes or until the back of the neck feels warm, then turn off the irons and let everything sit and cool down about an hour.

If the inlays in the fretboard are made of celluloid instead of real pearl, they should be removed. Sometimes real pearl are glued with hot hide glue and they need to be reglued after the heat treatment.

Maybe you should do a test run on a cheap guitar first of all! There is not much science in the method, it's a bit like rolling a dice. With experience the result will be more predictable.

Many thanks Roger. I'll have a think about this and maybe give it a try on a cheap guitar first. 

Is the piece of aluminium roughly the same width as the fretboard? How thick is it? Presumably the heat travels through the aluminium block , through the frets ( which are in contact with the block) to heat the neck? 

Andy

Yes, about the same size as the fretboard. Measured it to almost 5 mm thick. The aluminum distributes the heat through the frets and by the radiation of heat evenly and makes the bending curve even too.

Happened to make a heat bend on a back bowed neck today and took a couple of slides. The pressure is on the right clamp, the left one just keeps the iron in place.

Thanks Roger. Those pictures are helpful. Do you bother checking the temperature or just wait until you feel the back of the neck getting warm?

I did some temperature checking with the irons at first, now I just put the control in the right spot. The irons "cotton" temperature is effective, but pretty darn hot. Try somewhere around 100 degrees C, celluloid will start to melt somewhere in the 110 C region or so. I suggest you do some measurements and tests before doing the actual heating. With lower temperature, I let the iron(s) be on longer feeling the heat on the back of the neck.

Thanks Roger, I'll look to get these bits and pieces together and let you know how I get on!

Please do :-)

I can report that I overdid the neck bending in the pictures a bit, got a relief of about 0.3 mm. But a small corrective bending the other way made everything pretty much perfect. Tomorrow I will do the crowning of the frets after one nights hanging with tuned up strings and with a small weight on the guitar to settle the neck.

Good stuff. Does this guitar have an adjustable truss rod to help out?

No, but I have mounted a carbon rod in the neck. It's a 1890s George Bauer parlor guitar with a LOT of peal inlays :-)

Andrew, my setup is pretty much the same as Rodgers. Thing is, I have had consistently bad results. I have done I think 5 axes like this, and pretty much all were the same.  Usually what happens even after the neck cooling for a few days in a small back bow, I have had to repeat the process up to 5 times to get results.

This process worked better for me the two times when the fretboard was off. The other times, I had to do a full re fret after planing the fretboard, as it was a  slight roller coaster each time. 

  I had adult supervision from out own Luthier John Sharples too, so I wasn't just winging it the first few times. 

 This method seems pretty hit and miss to me, and wass pretty frustrating doing the same thing over and over again to get useable results that were permanent.

 If  the fretboard comes off, in your case, you can also replace that truss rod. 

Hi Kerry,

Thanks for that. I guess that's one thing that concerns me - the fact that wood seems to have a "memory" and will tend to revert to it's original position. My understanding is that the glue joint between fretboard and neck relaxes when heated thus allowing the neck to set in a slight backbow when the neck cools and the glue molecules set hard again. 

Maybe there's a step or two in Roger's process that helps keep the neck in it's new position? A couple of steps Roger refers to intrigue me - (1) soaking the fretboard with teak oil to prevent shrinkage and (2) after cooling, a night's hanging tuned up with a small weight to settle the neck. Were these steps included in your procedure?

I don't know, just surmising that it may have an effect !

I think I'll give it a try, just to see for myself how it pans out. The other thing I thought of was to remove excess relief remaining with a refret and introducing a bit of fret compression to straighten the neck out. I don't really want to resort to removing the fretboard unless absolutely necessary - the truss rod is still operational.

What does your Luthier John say about the process and the fact that the results were less than satisfactory for you - I guess he has the same problems when heating the neck?

Many thanks 

Andy

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