Threaded inserts for bolt-on neck?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by TJT79, May 2, 2016.

  1. TJT79

    TJT79 Member

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    A few guitar builders use threaded inserts in the neck, for true bolt-on construction.

    What hardware is used? Link?

    Can this be retrofitted to an existing neck (eg Warmoth)? Or does it need a specialised build?

    This seems like an improvement over just screwing into the wood of the neck. Any experience in favour or against?

    Cheers.
     
  2. Chris Pile

    Chris Pile Member

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    I've done it with the brass inserts, and with steel T-nuts. Works great, but installation must be very precise.
     
  3. John Coloccia

    John Coloccia Cold Supporting Member

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    I think you'll get a lot of different opinions here. IMHO, it's a downgrade from screwing directly into the wood, but it's worthwhile if you intend to take your neck on and off a lot. For example, Bill Kirchen travels (or used to, anyway) with his guitar by taking the neck off. But anyway, threaded inserts are still threaded into the neck, so they're still just held in with threads. The only thing that's changed is now you have an extra layer of metal between the bolt and the neck. If the joint is built right in the first place, you can probably twist the head off the screw before the standard wood screw strips out of the neck. In fact, I know you can because I've personally done it and I've also repaired guitars like that!

    The biggest problem is that for some reason the holes in the body are often too tight. They need to be clearance sized holes, and the screw needs to pass through unimpeded. If it hangs up, or even worse if it threads it's way through the body, the screw will never properly do it's job of pulling the neck tight to the neck pocket, and it can even act as a jack screw! It's friction that holds the neck securely in the pocket, and the screw should only be loaded in tension. When you break that formula, you'll have all sorts of problem no matter if you screw directly into the wood or if you use inserts.

    And as Chris says it must be done accurately. Some even install the inserts one at a time using the drill press and turning it by hand to make sure it's started dead straight. You'll have a hell of a bad time and nothing will work correctly if there's any sloppiness.
     
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  4. AdmiralB

    AdmiralB Silver Supporting Member

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    I agree that it's only worthwhile if you disassemble the guitar a lot. A lot. And then, only maybe.

    The critical interface is the butt of the neck against the pocket, where the string tension is applying force. The screws just need to clamp tight enough to resist the slight bending moment and (more importantly) prevent lateral shift in the pocket. There's no 'bonus points' for extra clamping force, and one can certainly exceed reasonable and prudent with wood screws.
     
  5. swiveltung

    swiveltung Member

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    If you are removing necks all the time maybe. I don't find it necessary for most use though. You can get little brass "thread -serts" at most Ace Hardware etc. Make sure the body holes allow the screws to turn freely. You will have to drill the maple neck out a bit at each hole location to put the insert in. Maple is hard, make sure you drill the hole large enough to get the insert in readily.
     
  6. TJT79

    TJT79 Member

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    I doubt I'll remove the neck much so probably not worth the hassle.

    If designing a neck from scratch T-nuts or similar between fretboard and the neck still seem like a good idea.

    Thanks
     
  7. walterw

    walterw Gold Supporting Member

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    i guess.

    like @John Coloccia said, properly done wood screws into maple are strong enough to crush the body wood beneath the corners of a bending neck plate or even break off the screw heads if you go too far. that qualifies as "already stronger than the wood" to me.

    heck, on vintage-type f-styles with the thinner neck plate you have to be careful to not crush the wood under the corners of the plate bending in by tightening too much.
     
  8. TJT79

    TJT79 Member

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    Ok, ok, you've convinced me! :)
     
  9. TJT79

    TJT79 Member

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    It was mainly the Sweetwood Guitars neck joint which got me thinking. Two machine bolts.

    Actually I think the Taylor electrics had a single bolt??
     
  10. walterw

    walterw Gold Supporting Member

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    sure, and that kind of stuff is cool with modern super-precise CNC-cut necks and body pockets, where it fits so perfectly tight you could almost take the bolts out and have it still hold together.
     
  11. claudel

    claudel Supporting Member

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    Steel inserts seem to work better for me than brass, but I've only installed a few sets on my own instruments...
     
  12. Shane Sanders

    Shane Sanders Supporting Member

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    Just to clarify, Sweetwood (and by proxy, me) uses an industrial T-Nut with a rectangular base with corner radii. In combination with the popsicle-esque isosurface of the neck and pocket, you get a lot better pressure distribution over a larger surface area than the typical neck pocket. It actually reduces the potential for cracking wood because the forces are distributed more instead of pulling like a wedge into the wood (which is how people split firewood with ease).

    [​IMG]
     
    Last edited: May 4, 2016
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  13. Shane Sanders

    Shane Sanders Supporting Member

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    In other words, the traditional method probably isn't best described as more than adequate force since it can splinter the wood, but rather a situation where it's really the wrong kind of force for the application. And in some instances the method backfires on us unsuspecting players. This little screen shot illustrates how the pressure points radiate from a localized pressure point--and I suspect this is mitigated in a good way with the thicker neck plates you can get to replace cheaper factory ones. The cheaper the neck plate, the more pointed the wedge of force because it buckles under the four pressure points. And this is made worse because the plate also has sharp edges which dig into the wood of the guitar body like a chisel. Easy to crack finishes!

    [​IMG]
     
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  14. Sweetwood

    Sweetwood Member

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    Why would you want anything different than super precise instruments?

    Having built necks 3 ways with wood screws, threaded inserts and T inserts I can tell you that it's not worth doing any kind of threaded insert. Just stick with wood screws. Tried and true and achieves ample clamping force. ...unless your wood is stripped, then go for it.

    However, the use of T inserts has allowed me to remove 2 screws entirely, create an ergo block and pocket, have more reliable coupling with longer service life. The other benefit is that with 3D coupling (eliminating the square block - halfpipe style), it leaves significantly more wood in the block and makes it way stiffer. The 3D nature of the pocket captures and transfers the energy better as well - resulting in longer sustain, better performance, higher resonance, more linear decay...things that are quantitative and measurable. Tone is tone, but if you like those characteristics, then it's a better system. One bolt would be more than sufficient as well. You don't need to make it super tight either. If it's too tight, wood deflection occurs and you can make indents in your fingerboard.

    [​IMG]
     
    Last edited: May 17, 2016
  15. walterw

    walterw Gold Supporting Member

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    no way dood, i gotta have the loose, spacious CBS fender neck joint so the two parts can breathe :)
     
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  16. AdmiralB

    AdmiralB Silver Supporting Member

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    Exactly. It's the contradiction to the proven rule. Like the three-saddle Tele bridge; on every other guitar and piece of hardware, we gotta have as much surface contact as possible (bridge studs, neck pockets, tailpiece studs, et al). But on Telecasters, we want the absolute minimum.
     
  17. Sweetwood

    Sweetwood Member

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    It's funny, for the pro players (guys who are really good and make a living from playing) all want intonatable saddles, huge frets (usually) and noiseless pickups, the bedroom hacks all want original equipment and noisy pickups.
     
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  18. poolshark

    poolshark Supporting Member

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    I've been ambivalent toward inserts for as long as I can remember, but it just hit me: The advantage to inserts and bolts isn't that they provide greater clamping force, but that their clamping force is much more easily measured. Given the variable rotational drag on a wood/screw setup, there's no way you could get an accurate torque reading. Using inserts and allen head bolts, you could torque them like lug nuts.
     
    Last edited: May 19, 2016
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  19. Boris Bubbanov

    Boris Bubbanov Member

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    A number of FMIC and other guitars use an embossed looking neck plate, often something that's composed of yellow base metal, and chromed over. Anniversary models; some signature models. Those aren't as strong as the steel neck plates - the added clamping force of the machine thread bolts will slough the corners of such plates right off. You might be better off with a stainless plate, maybe something 125% the thickness of the usual chromed steel neck plate.

    The other thing to think about is what Walter alluded to: We think of voids between the neck pocket and heel as "defects" but when the guitar falls and sustains a headstock strike, survival chances are much better if there's plenty of compliance in the heel to neck pocket join. Make it too high precision; cinch the fasteners down too tight and there's no mechanism left to attenuate the impact of the headstock strike at the heel to pocket join. This tends to mean the headstock fails, the heel shatters or the body wood at the neck pocket fails. Think about the way the Highway Department sets up overhead lighting poles - the bolts are engineered to shear off when enough force is delivered from the side - this can save the life of a trucker or other motorist. Sometimes it is actually desirable to have a "soft" failure at the neck join as opposed to a "hard" failure.
     
  20. Tone_Terrific

    Tone_Terrific Supporting Member

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    I'm betting nobody is testing guitars for impact resistance vs neck screw/bolt torque values.:D
    So much to do...sigh..:oops:
     

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