1930-31 National Duolian with neck issues

[Ginridge]

I was recently asked to restore this 1930-31 National Duolian with the crystalized finish. This guitar has deep family history being owned and played by the great grandfather of a friend of mine. He was an itinerate minister who played this guitar in his services. It hasn’t been played in years and is in fairly worn condition with a neck that is badly bowed, but otherwise intact. The family wants it returned to playable condition, but but does not want the wear and patine messed with. My kind of folks!

I’ll give everything a gentle cleaning and clean and lubricate the tuners, but the biggest question is how to address the neck bow. I’m leaning towards carbon fibre rods which I have done before, though I’d be curious to hear folks thoughts on the pros and cons of carbon fibre rods vs a truss rod in this particular application.

The bow is so severe that I’m wondering if I should heat press the neck to remove the bow before adding in any rods? I'll have to pull the fingerboard either way

Action @ 12th fret is 1/4”. All of this is neck bow; the heel is solidly seated and not loose. Should I try to take out all the bow BEFORE adding in carbon rods or a truss rod?

Here are some details of the instrument:

Mahogany neck, dyed fruitwood fingerboard
Steel body with worn, but intact crystalline finish
No physical damage to the body other than finish wear.
All original parts are there
Tuners functional but need cleaning and lube.

In my mind, I'm considering the following order of operations:

Full boogie inspection (nothing other than cleaning noted so far)

Remove fingerboard inlays and unscrew the fingerboard extension.

Remove fingerboard, heat press neck to flatten out bow. I know this doesn't always work or work well, but removing the bow before inserting carbon fibre rods or a truss rod seems like a smart move. After inserting either rods or a truss rod, I'd re-glue fingerboard. If that doesn’t cure all the bow, I can still do a neck re-set and shift the angle a hair. but I'm hoping if it all goes well, that may solve the problem.

Should I remove the neck before heat bending it straight again? Anything in particular I need to know about dealing with this crystal finish? I plan on only using warm water and perhaps a drop or 2 of Dawn to clean this.

Thanks very much for your thoughts and comments!

Here are a few pics to illustrate:

[PT66]

Many of the National metal body guitars have a neck that runs through the body. They are fairly easy to remove which make it easier to work on the neck. The last one I worked on had so much wear on the fingerboard that it would have been better to replace it. But the customer wanted to keep it original. Good luck.

[j. condino]

I'm a huge fan of those early Duolians. Necks were not the strong point. I generally like to have them leave the shop very straight and with no tension in the system, regardless of what extras carbon fiber I might add. The main variable is what style of music the owner wants to play.

As a buyer, my preference is for one with a dead or broken neck. Then I clone it and install a modern truss rod.

[Charles E.]

I was going to mention the screws in the fingerboard extension but I see you are well aware of them. Good luck with the heat treatment!

[rcc56]

Should you attempt to heat press the neck before installing reinforcement?

I would. That's a really bad bow.
If it were me, I'd be inclined to remove the neck unless I didn't think I could get it off without inducing further damage.

Whether I removed it or not, I would heat it gently for quite a while, so that it is good and warm [at least 100 degrees plus] all the way through to the back of the neck, then clamp it into a backbow and let it sit for at least a week before removing the clamps.
How much heat? Enough to encourage bendability, but not enough to blister the finish. You'll have to guess.
Repeat if necessary.

If you're really clever with clamping, you can clamp with a really stiff hardwood caul and use some shims to induce a backbow. Or you can make up a back-loaded caul. After you install your reimforcement, you might want to backload again, this time by only a millimeter or two when you re-install a fingerboard. You might want to consider using a new ebony board-- it will likely be stiffer than the old "fruitwood" board.

I might trust carbon fiber better than I would an adjustable rod in a case like this.

You'll need both plenty of horse sense and some good luck on this one.

[j. condino]

+1000 for the new fingerboard. Those originals are made from absolute junk material and often the wood has moved so much it is difficult to figure out what the scale should be. BUT- be glad that it is not a bakelite neck.

You'll also likely need multiple attempts to get the neck angle correct. The one thing that is a huge pain with these is every time you make a slight adjustment, you have to put the whole thing back together (again) and see if it worked. Very few people reset necks on these often enough to get it right on the first few attempts. I usually figure twice the bench time for one of these as for a dreadnought neck reset, just because I do that much more often. But... they kick @$$ when you get it right!

[Jeff Mando]

Something I found that helps when clamping a neck into a back bow is a 24 inch metal carpenter's level -- the old type is like a steel girder -- it won't bend. I make a U-shaped or V-shaped clamping caul for the back of the neck and use two (or more) hardwood blocks at each end of the fingerboard to create some space between the neck and the level to get a good back bow going when clamping.

Most of the new carpenter levels are synthetic plastic or super thin lightweight aluminum -- you don't want one of those. You may need to go to the pawn shop or a yard sale to find an old heavy-duty Craftsman level -- I got one not too long ago for a couple bucks at a yard sale...

[Chris Pile]

I've been doing repair for 45 years. Heat pressing almost never works.
It can only be repaired by planing the neck and installing something stiffer than the hollow tube.
Proper and competent repair won't be cheap or easy.

[pops1]

Gluing a quality fingerboard to a neck with a forced back bow has worked for me. Getting the back bow just right is a little tricky, but not that bad. There are frets out there with larger tangs, I have used compression fretting to straighten a neck, not sure it would straighten that much bow.

[Richard500]

Not having seen one of these in the flesh, or metal, is the back texture just zinc crystallization from galvanization? Hey, a rhyme!
If it is, it’s also under the paint everywhere. Careful cleaning that if you want it to remain crisp looking.

[pops1]

As far as I know that finish can't be duplicated so be careful what you do. A friend of mine had that finish and National couldn't match it at all refinishing it. That was several years ago, but the original process can't be done today, from what I understand. I would leave it alone, I like patina.

[rcc56]

National intentionally used a textured finish.

A few years back, I repaired a Gibson A that had a badly bowed neck by removing the fingerboard, heating the neck, clamping it into a back bow, and letting it sit for a long time. After it came out of the clamps, the neck still had a slight forward bow, so I planed it flat, reinstalled the fingerboard with a back loaded caul, and finished it up with a good tight fret job. The mandolin has since been sold, but the last I heard, it was still doing okay. I'll admit that it was a cross-your-fingers-that-it holds repair. If it ever does come back, I'll probably plane the neck flat and install a new, slightly thicker fingerboard.

If anyone wants to try this procedure, I would advise letting the neck sit in clamps for at least a week before removing them. Two weeks would be better. Then let it sit again for a few more days before trueing up the neck and installing the fingerboard.

[j. condino]

I spoke with a learning luthier friend just a few hours ago who used a heat blanket on a neck, something I do often. The phone rang and he got distracted....and forgot about it......until the neck got so hot it caught on fire!

No matter what one of us has done in the past on an old Duolian, your experience will be slightly different. Some combination of the above ways will solve it. That is the way of a skilled repairman- MUCH more difficult than being a new builder and in a constant state of improvisation because every day is a different task by a different builder from a different decade, for a different customer, with different expectations....

The go to person in the US who has figured out the duolian crinkle finish and does excellent work is Rik Besser of Bfanatic guitar works:

https://www.bfanaticguitarworks.com/...nal-resophonic

[Fretbear]

+1000 for the new fingerboard. Those originals are made from absolute junk material and often the wood has moved so much it is difficult to figure out what the scale should be.

That old fretboard will NEVER want to be any other shape than the one it has already curled itself into over the years. The same could be said of the neck as well until it is mechanically (physically, not steam) rectified. And as James says, it is junk and trying to re-establish accurate intonation (when it's unlikely it ever had it to begin with) on something like that rarely ends well.

[HoGo]

You certainly need to straigthen the neck as much as possible when you want to rout for CF inserts. Wood is quite plastic and with use of moderate heat application pressure and time it can be straigth again. Then the insterts and new strong fretboard will do their work.

[Chris Pile]

Part of the problem is that wood used to be alive.
And it responded to temperature, humidity, and barometric pressure as a tree.
It still wants to even though it's now dead.
That's why we get finish cracks.
The wood is expanding and contracting at a different rate than the finish.

[Ginridge]

Great info everyone! Thanks very much. I have a steel old neck heating bar I can warm up and remove the fingerboard with. So far the dyed wood fingerboard does not appear brittle or damaged so I'll see how it comes off. I know the family would prefer that I not replace fingerboard it possible.

I'm off for a quick gig today, but will start to tear into this on Friday and keep everyone updated.

[HoGo]

Part of the problem is that wood used to be alive.
And it responded to temperature, humidity, and barometric pressure as a tree.

The bend in neck is response to long itme exposure to string pull. So oposite forces (with help of some heat or moisture) can reverse this deformation that is still in plastic region.

If the family don't want to replace the fingerboard you need to make sure the neck is as rigid as it gets before you put back the old one. You probably cannot count with compression fretting as that dyed wood may be too soft for that to hold long time.

[rcc56]

My experience with "compression fretting" has been that it won't significantly straighten a neck, unless the instrument has the old-fashioned bar frets.
A good tight fret job will help to keep a neck from bowing later.

My experience with old dyed hardwood fingerboards has been that if they're not decomposing or completely rotten, they tend to be weak and brittle.
Yours might or might not hold. The chances of getting good long term results would be better by installing a new ebony fingerboard. If it came to me, I would probably leave it on the thick side.

If you're going to pull the board anyway, the amount of extra labor incurred by installing a replacement would be limited to shaving it to size and installing a few position markers. The extra materials cost would be maybe $50 for a CNC slotted board plus $10 for the position dots.

In my shop, I have to decide when structural integrity supersedes originality.

[Richard500]

The original question was whether to heat bend the neck before adding a truss or plain beam. Low temperature heat (far below the lignin softening point) will likely leave the mechanical stresses in place, so the graphite, or whatever, has to be stiff enough to take additional load. My last adventure was with square section graphite, and I stuffed the deepest possible section in a neck, square sides to have maximum epoxy strength. The difficult thing was figuring out how to hold a (bowl back) for milling a slot of variable depth.
If the neck wood is weak, as reported, truss rod anchorages at the ends might be poor.
And I was way off base with thinking the finish on these bodies was galvanize - appears to be something like mothballs in nitro; not to be tried at home!

[Ginridge]

Again, Thanks for the excellent feedback and comments!

I have to agree that replacing the fingerboard makes the most sense in this situation. I'm not sure the owners will go for that with the sentimental value etc., but I will make the pitch. In the meantime, based on comments above, I'll go ahead and remove the fingerboard screws and attempt to remove the neck for further assessment and to begin work. I agree that compression frets won't solve this issue, so I'm leaning towards removing the fingerboard and heat treating the neck to reduce the bow, then routing slots for carbon fibre rods. Depending on what I see when I get it apart and what I hear from the owners, I'll either replace the fingerboard or re-use the old one. I'll start work on this this weekend and will post pics.

That crystalline finish is apparently called a Frosted Duco Finish. Since I won't be doing anything to it but a mild cleaning, I assume it will be OK. I vaguely recall something about toxicity, but haven't found anything to back that up. If anyone has any experience with this, I'd appreciate their insights.

And Richard, I feel for you trying to hold a bowl back in place while working on it! I love bowl backs and have a bunch to work on as time permits, but that darned bowl makes it hard!

[Ginridge]

Well, I began last night and clearly, this is the first time this guitar was opened up! I was able to gently remove the white fingerboard extension dots and unscrew the fingerboard extension. Interestingly enough, two of the three screws (the ones on the outside edges) were screwed into small nuts embedded into little wooden strips on both sides of the neck bar inside the guitar.





When I removed the cover plate to assist removing the neck screws, I was astonished by the dust bunnies inside! I remember visiting the repair shop at Elderly Instruments years ago and seeing an impressive display of dust bunnies they had found. I have to say, this guitar's offerings rivaled anything there!





I was able to remove the neck screws and the tail piece, however, the neck did not come loose. As I inspected the inside, it looks like the support posts might be glued in place and are keeping the entire neck from coming loose.



Rather than pull all that out, I decided to try to remove the fingerboard first and see how things progress before going any further. I was able to get the board loosened back to the 10th fret or so just heating the fingerboard with a hair dryer, but since it's a vintage board of questionable material, decided to stop and will be removing the remaining fingerboard dots so I can use a neck heater to loosen the glue without ruining the position markers.

That's where things sit now. I'll update as I move forward.

[pops1]

The support posts shouldn't be glued, but there may be a nail down into the dowel keeping it in place. It' been a while since I had an old National apart.

[Ginridge]

Thanks Pops! I was actually surprised at how little I found online regarding removal of a Duolian neck. I'll look closer at all of this as I move forward. There were a lot of shims and wedges in place as well and I decided I should get a better handle on things before I undo them!

[Ginridge]

Today I made a closer inspection of the inside of the guitar and the neck joint. The support pads were in fact NOT glued in place (as suggested above) but the entire assembly was tightly held in place by multiple wooden wedges. A closer look at the neck joint showed something odd as well. On both sides of the neck bar where it went into the body, there appeared to be a glue of some sort.



I decided to continue as planned and remove the fingerboard. I used a steel bar neck heater (I was told might have come from St Louis Music) and heated the fingerboard 30 minutes to soften the glue.



The fingerboard came off clean and I clamped it flat to take out the bow. At this point I had warmed the body somewhat when I heated the fingerboard and I was able to wiggle the neck a bit and see the posts move, something I had not been able to do before. When I did that, a piece of the glue by the neck broke off.



It appears to be a hide glue of some sort and I get the sense that this is original work. I'm fairly certain that this guitar has never been opened up before. That white spot in this shot is actually the light reflecting off the glue inside the neck joint.



This is a fairly early guitar (1930 I believe) so National might have been trying different things but I'd be curious to hear if anyone else has come across this.

Once the fingerboard was off, I re-heated the neck for another 45 minutes clamped flat, then added shims to create a bit of back bow and left it to cool overnight. That's where things sit right now.

A couple other discoveries. I thought that this might have originally been a lighter color and the dark finish was a result of tarnishing and age but underneath the fingerboard and inside the body when the cone is removed, the original color was indeed black Duco Frost over silver paint.