Set Necks Vs Bolt On - Stress Question

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by Deed_Poll, Jan 29, 2019.

  1. Deed_Poll

    Deed_Poll Member

    Messages:
    3,080
    Joined:
    Jan 19, 2013
    I'm wondering whether some of the perceived difference in sound between a bolt-on and set neck (aside from the constituent that might be ascribed to general Fender vs Gibson differences - principally scale length and ferrous vs. magnetic pole pieces) might be down to stress?

    There's a big difference in that on a bolt-on neck, the bolt is exerting a constant force to hold the neck and body together. Even when you take the strings off, that immense compression in the neck heel and neck pocket is still there, an invisible

    By comparison, a set neck joint (once you remove the clamps) is no longer under that compression. It doesn't still have that internal stress in that area, just the tension of the strings and truss rod orthogonal to that plane.

    I'm not saying this is a problem as regards stability for bolt-ons, after all the way the neck and truss rod design vectorises and balances these internal forces in that plane is surely a fundamental part of what makes a guitar sound a certain way. But could it be responsible for some of that tonal difference we love to tell ourselves we can hear? ;)
     
  2. K-Line

    K-Line Vendor

    Messages:
    7,384
    Joined:
    Jun 24, 2006
    Location:
    St. Louis, Missourah
  3. Tres Mellow

    Tres Mellow Supporting Member

    Messages:
    385
    Joined:
    Feb 24, 2009
    Location:
    Corning, NY
    You might find this thread I just started interesting...
    https://www.thegearpage.net/board/i...take-on-designing-an-electric-guitar.2015000/
     
    paulg likes this.
  4. paulg

    paulg Supporting Member

    Messages:
    2,528
    Joined:
    Mar 18, 2005
    Location:
    San Rafael, CA
    I think you’d have to ask a Physicist not guitar players. Were too biased based on our experiences with Gibson and Fenders.
     
  5. DGDGBD

    DGDGBD Member

    Messages:
    6,425
    Joined:
    Jul 20, 2006
    Location:
    NJ
    the metal neck plate on the back of the body of the bolt on is also a notable difference in the makeup of the two. i doubt it would translate into something you can hear. here's an experiment, take a cheapo set neck guitar, then add a neck plate to the back, drill pilot holes and screw in neck screws tightening them down hard. play and record extensively before and after; and then see how they compare.
     
  6. Wass

    Wass Member

    Messages:
    14
    Joined:
    Jan 29, 2019
    Generally the modulus of elasticity for a material is not a function of its stress state (for small stresses such that it’s still in the linear elastic region). I think we can say with some confidence the answer is no. We could create some experiments to disprove it.

    As Tres Mellow points out, you will be interested in results I present in my presentation “Engineering an Electric Guitar.” If you don’t have good compressive stress holding the neck tightly against the body at their interface, you get micro motion that dampens string vibration. It can completely wipe out many modes of the string vibration and drastically affect tone. I share data that clearly supports this.
     
    wox and paulg like this.
  7. Timtam

    Timtam Member

    Messages:
    826
    Joined:
    Jul 22, 2017
    Location:
    Melbourne
    Great work. IIUC your FEM modelling actually showed that under 'normal' (?) screw tightening, the net forces (ie from string tension / bending moment) may actually be in the direction of opening up the neck joint instead of compressing it. And that only changing the wood thickness swung the balance to compression. So some bolt-on necks may not actually be under much compression on that interface ?

    I guess that one possible practical difficulty with comparing any given bolt-on neck guitar to any given glued-on neck guitar is that it is very difficult to know whether either has any air gaps or less-stiff-materials in the joint, and which structures are actually bearing the forces in those two cases, eg in a bolt-on is the longitudinal string force resisted by the back wall of the pocket, which it ideally contacts completely, or by the screws inserted through the body and neck at right angles to the string force (with less wood-to-wood contact at the butt end of the pocket) ? If the neck was drilled when there was less-than-total contact with the bottom of the pocket, then the screws will presumably bear more force ?

    However your results suggest that bigger machine screws / inserts, more tightening, and good pocket design can achieve good results.

    Re "you get micro motion that dampens string vibration. It can completely wipe out many modes of the string vibration and drastically affect tone." Do I take it that this likely vibration loss / cancelling is occuring via the neck rather than the body (as your results suggest that the body you tested was vibrating minimally at best, and that the flexible neck vibrates much more, and facilitates frequency losses) ? Or is it a characteristic of the neck joint alone ?
     
  8. Tone_Terrific

    Tone_Terrific Supporting Member

    Messages:
    28,104
    Joined:
    Dec 26, 2004
    Location:
    Canada-GTA
    Screws ought not be subjected to shear forces, rather they should exert enough compressive force to increase friction and hold against shear force that way.
    This can be shown to be effective as a neck can often be moved further into the heel pocket after wood shrinkage occurs.
    Interesting so far.
    You may interested in this thread looking at the comparative flex of quartersawn vs flatsawn maple and note John Suhr's explanation re diffuse porous and ring porous woods.https://www.thegearpage.net/board/i...uartersawn-neck.1608422/page-19#post-22909580
     
  9. Wass

    Wass Member

    Messages:
    14
    Joined:
    Jan 29, 2019
    To Timtam's points/questions:
    1. Most bolt-on necks are using wood screws and they have some regions, particularly at the "tip" of the body pocket, where they are not under compression. There is certainly some micromotion going on in these joints, and it is affecting tone. I would say it is affecting it negatively, but you know beauty is in the eye of the beholder, and there will be some who say they like that tone resulting from the lost information in the string vibrations.

    2. (a) I agree terrifically with Tone_Terrific that the purpose of screws should be to provide forces to bring the bottom of the neck into compression with the neck pocket. Wood screws are narrow and have VERY limited area in their side directions. Thus very limited stiffness can be achieved from this effect. (b) The butt end of the neck can be brought into contact with the side wall of the neck pocket and it can help to stiffen the interface between the neck and body, but you can just look at the ratio of these lengths and see that this will help in a limited way, and once again it would be hard to provide real good compressive stress at this butt end needed to prevent micromotion at that interface.

    3. Correct in that if a wooden shim is used between the body and neck it could be a source of compliance that would affect tone. I actually once saw a glued set neck come apart and guess what, the manufacturer had used a match box cover (paper) to shim the neck up prior to gluing. And people wonder why there can be radically different tone variation among guitars of the same type and manufacturer. (d) I have limited experience analyzing glued in set necks. My feeling is that, if it is done right, you would end up with the same result as a good neck-thru guitar. But I wonder if some of the manufacturers are using non-rigid glues, and then there are some who are sticking matchbox covers in there. Doh!

    4. The neck is flexible and participates in a big way to the vibration of the structure, and as I show with actual data, the vibration of the two points holding the string definitely affect the vibration of the string. The interface between the neck and body can drastically affect the neck vibration (and to a lesser extent the body vibration) and therefore also affect string vibration (therefore affecting tone). It's all one complete vibratory system where everything matters. You might be tempted to say the body participates least since it is the stiffest, but I would never make a blanket statement that the body doesn't matter. Clearly it does matter at least to the extent that it has to hold the neck properly! Also, I have shown that the vibration of the pickup itself can matter, and it is attached to the body. Well, unless for example it is mounted to a very flexible piece of plastic. You can take your guess whether this influences tone!

    To Tone_Terrific:
    1. I agree wholeheartedly that the purpose of screws should be to provide forces to bring the bottom of the neck into compression with the neck pocket. Sounds obvious, right? In precision machine design I have actually seen countless examples of engineers failing to understand this. One time I was sent all the way to Japan to diagnose a problem on a machine. I immediately determined their screws holding two parts together were "body bound." They had not provided enough clearance between the screws and the clearance holes. So the screws were rubbing on their threads. So even when those screws were torqued, we didn't actually know how much force was delivered by the screws to the joint between the two parts. I had them pull it apart and drill out more clearance in the through holes. I've seen this maybe 10 times by very good engineers so it's apparently not as obvious as it seems.

    2. Suhr saying that quartersawn wood tap tones at a higher frequency. Quartersawn is much stiffer in the direction 90 degrees to the grain lines. So if your goal is to produce a stiff neck, then yeah build with grain oriented 90 degrees to the flat part of your neck. The wood also has higher strength to resist stresses on the back of the neck. However, some people are actually NOT trying to build a stiff neck. They are orienting such that the neck is MORE flexible. You might get all kinds of more crazy dynamics where the neck is interacting with the string vibrations. That's the beauty of this whole subject, the possibilities are endless.
     
    Timtam and j.s.tonehound like this.
  10. Roe

    Roe Member

    Messages:
    7,258
    Joined:
    Jul 12, 2005
    Location:
    tromsoe, norway
    See if a bolt-on will change character if you loosen the screws? It won't sound like a set neck even then
     
  11. rockon1

    rockon1 Member

    Messages:
    11,449
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT
    I own 5 Ibanez RG's. Two are neck thru and 3 are bolt on. The most expensive of the bunch, the RGT3120 neck thru came with Dimarzio PAF pros. It was way too bright. EMG's fixed that. Somewhere down the line the the PAF pro ended up in the bridge of my bolt on RG570. Oops...way too bright. The guitars are all the same scale length, locking trem, etc.
    Thing is aside from the feel of the neck thru vs bolt on , mahogany vs basswood, etc the real impact, for me, was pick up choice.
    Does bolt on vs set or neck thru have an impact? Im sure it does. How important? -for me and my experience with very similar guitars I would buy another of either style without concern to bolt on vs thru or set.
     
  12. K-Line

    K-Line Vendor

    Messages:
    7,384
    Joined:
    Jun 24, 2006
    Location:
    St. Louis, Missourah
    Two identical built guitars can vary as much as two different design guitars. There is scientific proof at times but is it audible or meaningful. When I went through the designing of my pickups, I at first chased the resonant peak and ignored what my ear told me.
     
    galibier_un likes this.
  13. VaughnC

    VaughnC Supporting Member

    Messages:
    16,745
    Joined:
    Jan 4, 2002
    Location:
    Pennsylvania
    Yup, wood is funny stuff...and I'm not sure it can be analyzed in the same way metal can. Even cut from the same tree, two guitars can sound very different even if a species has tonal trends. Then it gets very subjective which one sounds better.

    Then, if you design a guitar for maximum sustain, it might subjectively sound like crap. Could it be that it's the crudeness of traditional designs is what gives the guitars we love their character? I've played Strats that sustained like crazy that sounded as bad as ones that were plinky and dead. To me, the ones in the middle of the "sustain road" tended to sound best. But that appears the way wood & sum of the parts works with a solid body guitar. But, even being technical by profession, I learned to try to turn that side of my brain off when I'm trying out a guitar and go with what satisfies my ears and hands with my eyes closed...and I usually end up with a better guitar fit.
     
  14. Brett Faust

    Brett Faust Member

    Messages:
    844
    Joined:
    Jul 22, 2008
    Location:
    USA
    WASS has a point in "Body Bound" set ups,but it seems nobody is addressing the obvious .
    What if there is minimal compression but no gap between the wood and screw threads on both body and neck? There needs to be minor compression when threading the parts together the 1st time and when reassembly is required after repair etc...
    You see, I frequently attach necks using very coarse but sharp threaded screws with undersized mounting holes ( minor diameter of the screws/ same size in neck and body). This approach prevents any movement and retains good contact of mating surfaces.
    I think It also sounds very good because there are no voids for screws to move within. It is also very important to get good contact on the floor of the neck pocket,but contact at the end or sides is not as critical. I like to have a tight fit as a point of pride myself.
    I have used this method for many years with great results. my guitars stay in alignment very well and sustain quite well with excellent tone. even without a neck plate or ferrules. There is only the threads holding things together, screw head is not under pressure and only serves as a way to drive them in.
    Just letting you all know there is more than one way to get there.
     
  15. Tone_Terrific

    Tone_Terrific Supporting Member

    Messages:
    28,104
    Joined:
    Dec 26, 2004
    Location:
    Canada-GTA
    Some feel metal inserts and bolts do a better job for both stability and tone.
    The problem is that nobody KNOWS.
    If a neck is shimmed leaving a small gap does all the tone change?
    Not that I have noticed. But who has quantified it?
     
  16. Wass

    Wass Member

    Messages:
    14
    Joined:
    Jan 29, 2019
    I have quantified all of that and yes it all can dramatically affect tone.
     
  17. rockon1

    rockon1 Member

    Messages:
    11,449
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT
    Peavey had a "Maxcess" aluminum neck joint for a bit....
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice