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Thread: 1930-31 National Duolian with neck issues

  1. #26

    Default Re: 1930-31 National Duolian with neck issues

    [QUOTE=Ginridge;1901766] 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./QUOTE]

    Agree probably a 29 or 30. 12 frets to body and flat (non-rolled) f holes indicate that. There should be a number stamped into the wood on the very top end of the peghead. I usually call Marc Schoenberger, he has a lot of knowledge about the details of these instruments and may be of some help. His number is available online. (National guitar repair)

  2. #27

    Default Re: 1930-31 National Duolian with neck issues

    Thanks, Jeff! Yes, the headstock number is C 230.

    Marc Schoenberger proved to be an excellent suggestion. I found Marc's website and gave him a call. He clearly knows his stuff and had some great info!

    He told me that being a '31, the fingerboard is NOT dyed wood. In 31, National was experimenting with phenolic fingerboards, a composite material, for fingerboards (shades of the bakelite neck!). It failed because it shrank over time causing the necks to warp. I think I read somewhere that over 1500 guitars were returned because of warped necks! Marc agreed with previous comments that that the fingerboard will need to be replaced since it has shrunk and curled and will continue to do so. That certainly explains the very odd nature of the material and the extreme neck warp.

    Marc was not surprised to hear about the glue in the neck joint and thinks I'll need to do a full removal of the neck to properly work on it. Re-setting the neck angle apparently is more complicated than on a standard guitar.

    As I thanked him for taking the time to talk, he wished me luck and told me he was glad this wasn't in his shop!

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  4. #28
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    Default Re: 1930-31 National Duolian with neck issues

    Those early Nationals are very thin metal compared to later ones. If you need to reset the neck there is a special technique for the National. I have reset the neck on one of the same vintage as the one you are working on. The thinner metal gives a wonderful sound, but is not as stable as the later guitars.
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  5. #29

    Default Re: 1930-31 National Duolian with neck issues

    Thanks Pops1! I'd love to know more about that process. Could you share details of the neck re-set process here or pm me if you prefer? I'm hoping to avoid having to disassemble and re-set the neck if I can, but I expect knowing the correct process is something I'll need, if not for this one, certainly for one down the road!

    Marc mentioned that the way the necks are set on these guitars, the neck angle has to match the angle of the top of the guitar between the cone and the neck. This angle is different than the angle of the rest of the body to the neck. So far, it does appear that if I can straighten the neck, I may be able get away with not have to disassemble the neck from the body (which I am afraid may damage the metal above the neck rod and will certainly involve destroying the shim that's holding everything in place). If that doesn't work out, I'll definitely have to remove the neck and I know from what Marc said, that will be a very different thing than re-setting a dovetail neck!

  6. #30
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    Default Re: 1930-31 National Duolian with neck issues

    If you look at the dowel stick on the National, it is thicker toward the neck than under the cone. Right where it goes from thick to thin you make a diagonal cut PART of the way thru the dowel stick. The cut will run from joint toward the front into the thicker part of the dowel stick. I wish I knew how to draw on a computer, alas I don't. In that cut you place a wedge to tip the neck back. The wedge is glued and screwed in place. With the metal on the early being so thin I doubt you will have to cut the heel. Somewhere there is a tutorial about this, but that was long ago, before the internet for me, and I can't remember where.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  7. #31

    Default Re: 1930-31 National Duolian with neck issues

    That sounds similar to what Marc was talking about. I'll keep searching and see if I find that tutorial.

  8. #32

    Default Re: 1930-31 National Duolian with neck issues

    rcc66 mentioned "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."

    I'm back in off the road (SERFA conference) and looking into replacing the fingerboard as suggested with a new ebony one. The owner wants it to be a radiused fingerboard and I was talking to LMI about having them slot and radius a new board for me. They mentioned, though, that they don't do position dot cut outs. I'd prefer to have that done during manufacture if at all possible since I don't have access to a drill press and I want to make sure I get the holes for the screws in the fingerboard exyension exactly right. Is there a fingerboard supplier that does include the dot cut outs?

  9. #33
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    Default Re: 1930-31 National Duolian with neck issues

    You're overthinking/over-worrying.
    A drill press is nice for drilling for dots, but not at all essential.

    Clamp the fingerboard to your bench [if you wish]. Drill a small pilot hole. Stand up your drill with the dot sized bit in the pilot hole. Rest your elbows on the bench to hold it steady and look at it from several angles until it's as plum as you can get. Pull the trigger. It will be close enough.

    Measure twice [carefully], mark carefully, and cut once. Use reasonably fresh bits.

  10. #34

    Default Re: 1930-31 National Duolian with neck issues

    OK... You talked me into it! I'll let you know how it goes.

  11. #35
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    Default Re: 1930-31 National Duolian with neck issues

    If you have any doubts, find a piece of hardwood scrap and practice. That will also tell you whether your bit will work on hard wood without tearing it up.

  12. #36

    Default Re: 1930-31 National Duolian with neck issues

    Well, much news to report and a new issue to seek advice on. I had hoped to have a friend of mine assist with the tapering the new fingerboard blank I ordered from LMI (I only have a table saw) but unfortunately, a case of Covid put him out of the running. I ultimately called Luthier's Mercantile to see if they had a jig for a table saw. They said they didn't, but told me what to look for and I found a Rockwell tapering jug for a table saw that works well. I was able to trim the fingerboard correctly on another lower valued instrument and just cut the new fingerboard for the Duolian today. My original plan was to route slots in the neck and put in Carbon Fiber Rods, but the neck has completely straightened out and I am wondering if I need to do that now. The new fingerboard is a good 1/16th thicker, Ebony, and has a very slight taper. Would the new fingerboard be enough to hold the neck straight or should I still add in carbon fiber rods?

    Another issue that has come up is the location of the screws holding the fingerboard to the body. On the original fingerboard, they are off centered but between the 16th and 17th fret. With the new fingerboard, they very nearly come under the 17th fret. I checked back with LMI and they indicated the older fretboards can be very erratic, frequently cut by hand. I did check and the scale is correct, but the fret slots do vary between the two fingerboards. I am assuming that the LMI board is more likely to be accurate since the old fingerboard was a composite material that shrank.

    Under the circumstances, I see only a few possible solutions:

    1) Drill the fingerboard to match the screw holes, then inlay ebony over the recessed screw heads and cut new slots. I will also have to then cut 2 pearl dot holes in the middle of the space between the frets

    2) Expand or move the drill holes in the top of the metal body so they land in center of the space between the 16th and 17th frets. The pearl dot would then go over the screw heads as they do now.

    As I am writing this, I am leaning towards moving or expanding the screw holes in the top of the instrument since the fingerboard will cover them but I'd appreciate anyone else's thoughts on this one!

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  13. #37
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    Default Re: 1930-31 National Duolian with neck issues

    Double check the scale length befor you do anything.
    Measure the distance from the nut end of the fingerboard to the 12 fret. Double that figure, and you have the scale.

    Then secure the fingerboard to the neck in its correct position and measure the distance from the nut to the front of "saddle" part of the bridge.
    If the saddle is staight, this distance should be scale + 2 or 3 mm. If it is angled [which would be better], the ideal distance would be scale + 2 1/2 mm at the first string, and scale + 5 mm at the sixth string. You can be a millimeter or so short, but not much more than that if you want the instrument to fret in tune.
    If you play with a slide only, you've got more room for error.

    If everything is within tolerance, you're good to go. If not, you might be able to get away with moving the fingerboard forward or back a little bit; and/or by rotating and/or re-working the saddle to get things "close enough for gov'mint work."
    And if the screw holes in the body are in the wrong place, move the screw holes rather than trying to stick the screws and inlays under a fret.
    If you're afraid the new holes are too close to the old ones, you can scoot the double dots inward a millimeter or two to compensate.
    Measure 3 or 4 times before you pick up your drill.

    As far as adding a rod [one would do], your call. If the neck is good, thick, and stiff, and your fingerboard caul is good and straight, it might be fine. Or, you can backload the neck a tiny bit if you're clever enough to devise a way to do so-- perhaps a short cardboard shim between the caul at the nut end of the board. If you do add a rod, I suggest recessing it slightly below the surface of the neck and covering it with a wooden filler piece. That's because carbon fiber is miserable to level once it's been installed.

    Me, I prefer not to take a router to an old neck unless I feel it's absolutely necessary.
    Last edited by rcc56; Oct-02-2023 at 8:08pm.

  14. #38

    Default Re: 1930-31 National Duolian with neck issues

    Thanks rcc56. Great advice!

    I had another conversation w/ LMI about this and realized that being a composite board and having shrunk (which was the cause of the neck warp) it actually was no longer accurate to measure the scale with. I had made the original measurement exactly as you suggested, but the fingerboard had shrunk enough to make that measurement inaccurate. I realized this when I put the cone in place to check the final scale length Based on the fingerboard measurement method it should have been 24.875. When I measured from the nut end of the fingerboard (based on the original nut and previous "ghosts") up to the saddle on the biscuit cone, I came up with 25 1/8. I realize you mentioned a few extra mm. I'll need to measure and see how close it is.

    If everything is within tolerance, you're good to go. If not, you might be able to get away with moving the fingerboard forward or back a little bit; and/or by rotating and/or re-working the saddle to get things "close enough for gov'mint work. And if the screw holes in the body are in the wrong place, move the screw holes rather than trying to stick the screws and inlays under a fret. If you're afraid the new holes are too close to the old ones, you can scoot the double dots inward a millimeter or two to compensate.
    Measure 3 or 4 times before you pick up your drill.


    That all makes perfect sense. Depending on the final measurements, I think I can try to slide the fingerboard down about a 32 or so. God is in the details.

    I've done about 1/2 dozen of the carbon fiber rod implants and while I can do them well enough now, like you, I prefer not to route an old neck unless I need to.

  15. #39
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    Default Re: 1930-31 National Duolian with neck issues

    Put in the 12th fret and put two strings on. You can then move the fingerboard to intonate at the 12th fret. Drill a small nail sized hole, two is better to locate the fingerboard to glue it on and you will play in tune. I have done this with old Nationals that don't play in tune and it works well. You may have to clamp the headstock to the bench to keep the neck from bowing, when the new fingerboard is glued in it will be stronger, but you don't want it to bow to set your fingerboard. You will we doing something similar to what rcc56 is saying to backbow the neck, but here you only want to keep it straight.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  16. #40
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    Default Re: 1930-31 National Duolian with neck issues

    I don't have the instrument and new board in-hand, so I'm not sure what you're dealing with.
    There are several possible solutions, depending on what you've got.

    If the board is too short to work with, several possible solutions come to mind.

    1. Have a new board cut and save your current replacement for another project. It might work on the right Martin-- their "short scale" has varied over the past century, sometimes as long as a true 24.9", sometimes closer to 24 3/4", sometimes it appears to be about 630 mm [24.803"].

    2. If there's room to scoot the board forward but the board has been narrowed too much, you could widen the board with thin black wood binding strips. You could treat it like any other bound fingerboard and undercut the tang on your fret ends; or if you want the fret ends to show, get out your slotting saw and extend the slots right through the binding. If you get a good glue joint and dye it with Fiebing's black leather dye, nobody will be able to tell you've widened the board unless they stick their nose right on it. Or bind it with ivoroid, like a style O. To avoid a huge nut, a little light brown aniline dye and a couple of wipes with a q-tip dampened with shellac behind the nut will mask a few sins.

    3. Modify the biscuit bridge and put the saddle where you want it. Or make a new homemade biscuit bridge.

    4. [least preferred]-- Shorten the neck heel slightly.

  17. #41

    Default Re: 1930-31 National Duolian with neck issues

    Pops1, Interestingly enough, I tried what you suggested, and added in a temp. 12th fret and strung up 2 strings to check intonation. Amazingly enough, I had to slide the board farther BACK UP the neck in order to intonate it. This is exactly opposite of what I had expected based on the measurements. I did have the shim the original bridge but the action looks roughly close at the moment. This is my first work on a biscuit resonator so I'm still a bit green on the final set up. I also cut the fingerboard just a hair wide so I can move the board as needed in either direction with no need to widen it.

    I will look into adding a bit of back bow as I glue on the fingerboard. I've done this when I add the carbon fiber rods, but this one is a different animal so I'll ponder before I do anything! I have decided to go w. rcc56's suggestion of relocating the screw holes in the top so they are centered between the 16th and 17th frets.

    Thanks for the great advice. I'll keep you posted as I go along!

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  19. #42

    Default Re: 1930-31 National Duolian with neck issues

    I just glued up the fingerboard. I've used the set up I use when I route the carbon fiber rod slots to create a mild back bow and, as suggested, had drilled two pilot holes to keep the board in the correct location. I used fish glue for it's longer clamp up time and big rubber band strips to clamp the board in place. I'll let it all sit overnight and see how it looks tomorrow. I had to clamp the heel and fingerboard together since the neck was not screwed into the top yet and otherwise there would have been a gap at the body end of the fingerboard. Once this is done, I'll drill the new screw hole locations and position dots.

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  20. #43
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    Default Re: 1930-31 National Duolian with neck issues

    I think it is common to have to move the fingerboard away from the cone. I usually have the cone all the way back and wish it would go more, so this doesn't surprise me. Glad it is working out for you.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

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