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National Resphonic Neck Reset

8/5/14

 

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 1. A National Guitar.  This is a polychrome tri-cone built in 1996.  It’s a cool guitar for sure! 2. High Action.  The guitar is hard to play and the customer wants low action.  Unfortunately the action can’t be lowered enough at the saddle because the break angle is pretty low.
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3. A Low Saddle.  The saddle sits in a T-shaped bridge that rests on the 3 cones inside the recessed area called the sound-well.  I’ll have to change the neck angle in order to lower the action. 4. The Neck-Stick is the hidden part of the neck.  The stick is glued into the heel of the neck and travels the length of the guitar body where it is held in place by a bunch of screws and shims, kind of like a replacement window.
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5. Hidden screws in the fretboard tongue are concealed beneath the ivoroid dot inlays.  I’m drilling out the dots and removing all of the screws.  The center screw is quite long and attached to the neck stick itself.  The other four screws are smaller and go through the top of the guitar and secure a thin maple block inside the guitar. 6. Inside the Guitar.  The neck stick enters the body of the guitar through a rectangular opening in the side where it is attached to the maple block, top and fretboard tongue by the hidden screws.
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7. Removing the Neck.  With all of the screws removed, I’m sawing through the top of the posts with a thin-kerfed pull saw.  Once the posts are removed, the neck will slide out through the opening in the side of the guitar. 8. The Heel of the neck is back-cut so only the outer 1/16″ or so of the heel is actually contacting the side of the guitar.  Since the heel of the neck is the fulcrum point, I will establish the new neck angle by cutting a wedge-shaped slice off of the heel with the thick end of the wedge removed at the “heel-cap”.
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9. Sanding the Heel “Cap”.  I’ve scribed the heel cap to mark my maximum depth of cut as determined by Stu Berg’s neck reset math formula.  At about a 45 degree angle, I sand the heel cap with PSA sandpaper on a paint stirring stick to just shy of the scribed line. 10. Cutting the Heel.  I’ve scribed more lines on the sides of the heel from the sandpaper cut on the heel cap to the end grain of the heel at the bottom of the fretboard tongue.  I use a very sharp chisel to cut away the waste.  When I’m done, I’ll back cut the heel so only the outer 1/16″ will contact the sides.
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11. Trimming the Neck Stick.  I’m removing a thick wedge from the top of the stick with a block plane.  As I change the neck angle the headstock will pull back.  If the guitar were laying on a table with the strings facing up, the headstock will move toward the table as the neck angle changes.  The fulcrum point is the neck heel, thus the neck stick will move up away from the table as the neck angle is reset. 12. Trimming the Neck Stick beneath the fretboard extension with a chisel will once again give the maple block space for shimming.  I’m frequently test fitting the neck to be sure that I remove the minimal amount necessary from the neck stick for the heel to once again contact the side of the guitar.
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13. Fine-Tuning the Joint.  I pull 220 grit sandpaper between the body and the neck to precisely fit the heel to the contour of the guitar’s side.  Because of my careful layout and chisel cuts the neck correctly aligns laterally; the screw holes in the neck stick match up to those in the sound well.  If the screw holes did not align laterally, now would be the time to make those adjustments to the heel. 14. Test-Fitting the neck, everything looks good.  There is now a gap between the rear-most post and the bottom of the neck stick.  In order to strengthen the modified neck stick I’ll make a wedge to glue to the bottom of the stick, bringing it back more or less to its original dimensions.
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15. Hand Planing a wedge from quarter sawn cherry.  This wedge will also allow me to reuse the original posts.. 16. Gluing the Wedge to the bottom of the neck stick.  I used hot hide glue and a bunch of clamps.  Two finish nails in the sound well screw pilot holes help keep the parts aligned.  After 24 hours I’ll remove the clamps then hand plane the sides of the wedge flush with the neck stick.  An application of black dye will make the neck stick reinforcement visually subtle.
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17. Assembly.  I’ve screwed the neck stick to the center and rear-most sound well pilot holes.  A small shim between the fore-most sound well screw and dowel stick pulls the heel flush to the side of the body.  With the heel in place it’s now a matter of shimming the neck stick and reattaching the remaining screws.  I’ll shim the neck stick at the same points that the factory did. 18. Adjusting the Fretboard Tongue.  I loosely fit the four screws that attach the tongue to the maple block then fitted a couple of shims between the top and the maple block.  I then snuggly fit a wedge shaped shim between the top of the neck stick and bottom of the maple block and tightened down the center screw.  Now I’m tightening the four screws that hold the fretboard tongue to the maple block.
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19. Shimming the Side of the Neck Stick.  A thin shim fills the gap between the bass side of the neck stick and the opening in the side of the guitar.  The treble side of the neck stick is pressed firmly against the opening in the body. 20. Refitting the Posts.  The fore post is a touch too tall.  I’m trimming it down until the post fits snuggly between the bottom of the neck stick and the back of the body.
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21. The Fore Post is set. 22. The Rear Post is set.  There was a thin gap between the rear post and the neck stick which I glued and shimmed in place.
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23. The Tailblock.  I shimmed the gap between the neck stick and the tail block in the same fashion as the original factory shims. 24. New Dots cover up the screws at the fretboard tongue.  National was kind enough to send me some replacement dots for the fretboard.  They are 1mm larger than the originals which doesn’t bother the customer.  I glued them in place, now I’m trimming them flush with a sharp chisel during the refret.
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25. New Frets.  The refret gave me a chance to sand a slight warp out of the fretboard and sand the fretboard to a truly flat across the grain profile. 26. New Saddle.  I made a new saddle out of hard maple with plenty of height for future action adjustments.
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27. The Heel appears as it did before the reset. 28.  All Done.  The guitar has low action, a straight neck and some silky smooth new stainless steel frets.