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Installing a "truss rod" after the neck is done??

Posted by Dan Sleep on February 26, 2010 at 8:55am in Building Secrets, Tips, Advice, Discussion
My latest 4 string build evidently needs some structural support in the neck, since it seems to bow a bit too much after I get it strung up and tuned. I am torn between just making a whole new neck, or adding some support to the existing one.  The existing one is a bolt on, so I don't have to destroy the box to work on it.

I was toying with the idea of just removing the hardware, putting the neck on the router and cutting a slot in the back, and gluing either a rod or a piece of flat steel in the slot, and then covering it with a piece of wood, then sand and finish.

Is that likely to add enough support to keep it from bowing?  Currently it raises the action so much that the higher frets are almost unplayable, the strings are so high.

Waddya think?

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Replies

  • Dan Sleep March 1, 2010 at 4:48pm
    You were exactly right, it was the box and not the neck. I was kind of heading that direction eventually, but your suggestion was right on. I glued in a small piece, well, a big piece, of angle iron to anchor the neck support block to the box, and it did the trick. I needed a small shim under the neck to fine tune it, but it is where I want it now.

    soulpatch29 said:
    If the neck isn't doesn't go thru to the bridge part of the box, It maybe the box that needs support and not the neck.
    • Tim Lang > Dan Sleep March 6, 2012 at 4:59pm

      I've got a similar problem.  When I cut my neck out, I cut a gap out of the section that's inside the box, which is where it's bending.  I also used heels at the spot where both ends contact the box (for more gluing area).  I think the heels are slightly too close together, which is putting pressure on the box, which is responding by bending in slightly, and also bending the neck inside the box.

       

      What I'm wondering is that if I could remove one of the heels, and glue an extra block of wood underneath the neck where it's bending to help support it.

       

      I want to make as few modifications to the box as I can, because after I strung it up, it sounded great.  Nice and loud and full (which was something I wasn't expecting)

       

      Here's a pic of the neck in question:

       

      photo-1.jpg?t=1331065446

       

      • ChickenboneJohn > Tim Lang March 7, 2012 at 2:37am

        Tim, if that neck is bending it will be bending most at the thinest part, i.e. where it goes through the box. It looks around 3/8" thick : think about it - if you made an entire neck 3/8 thick you'd expect it to bend wouldn't you?

        I'm not sure why you've put on those "heels" - unless it's as a decorative feature, as they don't add any strength at all.

        Here's couple of mine  I'm making right now -  the one at the back is a thru' neck, the one in front will be screwed onto a centre block. See how the thickness is maintained inside the box..right where you need the strength. The heel is just the transition from the neck to the thicker part inside the box. By cutting the part of the neck down to a really skinny thickness at the end of the fretboard you've effectively created an unsupported  hinge-point where the neck will start to bend, and it will bend along it's entire length too.

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        • Tim Lang > ChickenboneJohn March 7, 2012 at 1:12pm

          yeah, that's what I figured.  I checked with a straight edge last night and it was bowing in the thin spot.

          I added the heels on there to add extra surface area for the glue to stick to.  (and I thought it looks nice).

          last night I pulled off the back heel and glued an extra thick piece of maple to the thin spot that goes through the box.  I'm going to string it up tonight without the box and see if there's any bowing from string tension....

      • Habanera Hal > Tim Lang March 7, 2012 at 12:21am

        I'd glue a 1x support beam down the center of the box bottom (in the area between the heels), then lay your neck into the box on top of that and bolt your neck to it. That sucker won't go anywhere then.

  • Dan Sleep February 28, 2010 at 9:17am
    Yea, I am going to check that today, and see if it needs reinforcing.

    soulpatch29 said:
    If the neck isn't doesn't go thru to the bridge part of the box, It maybe the box that needs support and not the neck.
  • soulpatch29 February 27, 2010 at 10:00pm
    If the neck isn't doesn't go thru to the bridge part of the box, It maybe the box that needs support and not the neck.
  • Christopher Call February 27, 2010 at 7:11pm
    Martin did have that square steel tube like thing. Stew-Mac sells them fairly cheep should you go that way. that is the only way I would go other than an actual truss rod!

    Grizz said:
    A truss rod is used to add or subtract bow in the neck as well as stiffening. Martin guitars in the 60's, I think it was, used square channel steel for truss rods for stiffening. They were not adjustable.
    I agree with Matt, if you have a fretboard take it off and route a channel, insert the rod and reattach the fret board. If not, inserting it at the bottom would also work.
  • MichaelS Country Boy Guitars February 27, 2010 at 12:17pm
    Try to find some 5/4 lumber, it works out to 1 inch when done, for your next neck. I like the feel of a 1" neck and the extra 1/4 inch really makes a difference.
  • Dan Sleep February 27, 2010 at 11:59am
    I use the standard 1x2 from Home Depot for all my necks, so it is 34 inch thick.

    I used light gauge strings, and in fact, I use light gauge strings on all my builds.

    I have some tests I want to perform in the next day or so. I want to be sure that the structural support "beam" I glued to the inside of the box, the one that the neck and tail piece bolt to, are not causing the problem. If that is the problem, then I may have to reinforce the box itself rather than the neck.
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