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bolt-on neck - helicoil inserts

Discussion in 'Luthier's Corner' started by Rodent, Nov 30, 2005.


  1. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    Just thought I'd drop an advance note that I'll be testing helicoil inserts in my bolt-on necks the next couple of weeks.

    In my progression away from the traditional wood screw, I have utilized threaded steel inserts on Fender necks with excellent results. On one specific application to an otherwise stock P-bass, the installation of these inserts eliminated the traditional deadspot on the G string - the bass arrived with this condition and left free of this defect (and is still deadspot-free after three months of regular studio/live usage)

    The threaded insert is a great solution for a retrofit, but not necessarily ideal for new construction. I considered utilizing Tee nuts prior to adhearing the fingerboard/fretboard, but it just has a hassle factor I'm not willing to accept at the moment. Then I read some on different luthiers exceptional experiences of simply threading the neck wood itself.

    I don't like the diminished durability of maple threads, but I do like the simplicity of drilling/tapping a pilot hole and 'winding in' the stainless threads (I've installed helicoils in many, many hy-shear inserts on annodized aluminum electrical cabinets in my early years.) Currently I'm looking at 10-24 threads, but I'll also be testing 10-32 and 1/4-20 as well. All testing will utilize stainless machine screws. I'll post my results and a set of images when this round of experiments is completed.

    All the best,

    R
     
  2. Basschair

    Basschair .............. Staff Member Supporting Member

    Feb 5, 2004
    Stockton, Ca
    I only got to skim your post...can you let me/us know where you picked them up and did that place have matching bolts included? I've considered the inserts, but didn't know where to start. Thanks Rodent!
     
  3. rubo

    rubo

    Aug 25, 2003

    Do you have any pictures left from that installation. Was it placed in the same spot as the original screws? What depth and width size threads / bolts did you use?

    Cheers
     
  4. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    one source is McMaster-Carr (www.mcmaster.com) where you can look for part No. 91732A719 You can also obtain the stainless screws here as well, but they do not come as a pre-configured kit.

    in order to do this, you'll also need to obtain the insertion tool - for a 10-24 thread look for part No. 90261A154 after you first sit down (but this is cheap compared to the tool for a non-tanged helicoil), and also a bottoming tap 91709A428 (if you don't install these prior to attaching your fretboard) or a plug style tap 91709A104 (if you have a thru hole before the fretboard is installed) To finish the job, you'll also need the tang break-off tool 92955A109

    This is quite an expensive initiation to acquire all of the needed tools, but once you have them it's a relatively simple job to install these properly. I have several 5-string basses (made by a friend) with helicoils installed, and every one has performed exceptionally for over five years. It's finally come time for my turn to do my own installation homework/experimenting.

    All the best,

    R
     
  5. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    Identical place as the original wood screw holes. I did need to drill the holes larger, and used 10-24 screws. I don't recall the length right now, but I can back one out later and give it a quick measure.

    Key to success with the threaded inserts (not the helicoils - different subject) is to utilize a drill press or horizontal boreing machine and forget any temptation you may have in using a hand drill.

    Here's an image from my earlier detailing of this activity:
    [​IMG]

    All the best,

    R
     
  6. rubo

    rubo

    Aug 25, 2003
    The problem I've encountered the most is once you drill the holes in the neck, it's hard to screw in the thread at a precise 90 degree angle and not to ruin that angle. How do you go about using a press drill to screw in the thread very precisely?

    Cheers
     
  7. Rod, I might be able to save you the trouble and expense of testing the 1/4-20's - They work well as you might expect - they'll hold about 500 lbs per bolt but they are too large in scale for the smaller area of in the back of the neck pocket on Fender style basses. The heads of the ovals won't fit the neckplates and they are about twice the circumference of the 10-24's. You also won't find suitable ferrules for these bolts. I suppose you could use cap screws for a smaller look but they are fairly thick so you'll lose some depth under the neck. I used the 1/4-20's on my first build and this is what I found.
     
  8. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    Thanks Allan! I'm really shooting for the 10-24's to work out and will gladly forego the expense of the additional 1/4"-20 installation tool set ...

    On the single-cut bolt-on design I'm working the final nuances on, having the helicoils (vs traditional wood screws, threaded inserts, and/or Tee nuts) is critical for joining the neck along the upper horn.

    I'm also considering using helicoils for attaching the bridge on one bass to see if there is a significant sonic difference between wood screws and machine screws into helicoils. I know it's a ton of extra work for a bridge that is already secured tightly enough - but it'll only be on one test bass for now, and ya never know what sonic gold could become of it.

    All the best,

    R
     

  9. PM thisNSucks and ask about his Steve Harris P replica. I installed inserts for the BAII bridge on that one and he swears by it. It has an alder body with a maple neck so it should be a good empirical candidate.
     
  10. jeffhigh

    jeffhigh

    May 16, 2005
    I have used helicoils before, into metal with mixed results,most good machine shops will not use them, especially in aluminium.
    I would think they would be the worst choice for a screw to timber interface.
    What you end up with on the outside is a fine thread with a rounded outer edge with no interference fit to the wood.
    There is a reason wood threads are coarse and sharp, it works.
    try it on some scrap first if you must.
    Jeff
     
  11. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    Jeff,

    Your post in interesting, in that it contradicts so much of my prior experience ...

    * helicoils into aluminum: have you ever hotrodded a Chevy or Ford aluminum small block before? Most all of the aluminum parts that contain the bolting threads utilize helicoils. I used them as noted in my original post for 'Grade A' / 'High Shock' systems on combatants (i.e. nuc delivery control systems) And let's not forget that Boeing has certified their usage for securing aluminum airplane parts.

    After a couple of re-reads, I keep thinking that you're thinking of a different product than a helicoil thread insert. Here's what I'm referring to:

    [​IMG]

    and how it's used:

    [​IMG]

    Also, take a read here for a technical discourse on the established use of helicoils in the aerospace industry.

    http://www.manufacturingtalk.com/news/hec/hec103.html

    http://www.dhayaghem.com/bollhoff/Helicoil-Catalog/helicoil-cat-p5.htm

    All the best,

    R
     
  12. Hookus

    Hookus

    Oct 2, 2005
    Austin, TX
    Good points, this is what I was thinking, but then again, I have not tried them:

    I think the friction-fit principle behind them was really made to work with hard materials. I used these pretty extensively to repair radios in the military, when an aluminum screw broke off in the chassis, we would drill out the whole shebang and put a coil in it. I think they would have significantly less holding power than a wood screw, they have much smaller threads, and remember, the screw to coil bond may be invincible, but the coils will pull out of the wood before a properly driven wood screw.

    Besides, I cannot imagine wood screws being a problem unless you routinely loosen and tighten the screw. Most guitars probably only ever have the neck removed one or two times in their lifetime, most likely for repair, which should be done by someone qualified anyway.
     
  13. jeffhigh

    jeffhigh

    May 16, 2005
    Ok, it's been a long while since I used them, don't remember the profile. Havent done chevys, but when I was into air cooled VWs helicoils were frowned on and I think Time-serts were the go. Perhaps due to the crappy metal used for VW engines
    Regardless, the fine threads into wood is the major concern, It may be adequate but will probably fail well before the screw.Would suggest a pull out test with the fastener through a plate blocked out from the surface.
    regards
    Jeff
     
  14. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    hi Jeff,

    just re-read my post above ... and it sounds like I'm being harsh on ya. not what I had in mind while I was typing - more of an attempt to discuss it out was what I was thinking.

    apologies if you think I was bashing on you ...

    All the best,

    R
     
  15. jeffhigh

    jeffhigh

    May 16, 2005
    No problems rodent, we have obviously had different experiences with helicoils.
    My main concern with what you are proposing is the insert to wood interface.
    Do you have a width restriction that prevents you using an insert designed for wood?

    Jeff
     
  16. jlt

    jlt

    Apr 24, 2004
    Fullerton, CA
    Rodent,
    Please keep us posted on how it turns out. I'm very interested in hearing how it will turn out. A couple of questions for you. Which threaded steel inserts did you use for those fender basses? And where can you get them? I'm thinking of trying some out on a bass I plan on building.

    Thanks
    james
     
  17. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    On the single-cut bass I'm finishing the details for, I have a width restriction on the upper horn. If there was a little additional width I could easily utilize a threaded insert like I've used on other basses ... but this is a little close for comfort. It might not be any problem at all - but I'd rather err on the side of caution for the first one.

    All the best,

    R
     
  18. jeffhigh

    jeffhigh

    May 16, 2005
    love to see some details of what you intend ( I used to be a structural engineer)
    Jeff
     
  19. And the real answer IMO as to why wood inserts use knife threads is twofold. First, it's to create strength when connecting pieces of soft wood with machine bolts - the exact application that wood inserts are designed for. Second, it's to make installation easier because they cut into the material quickly and with less force. It's my opinion that we bassists are using them for a tangential purpose - to increase the clamping force beyond the perfectly servicable levels offered by wood screws and to allow multiple neck removals without the concern of eventually wallowing out the mounting holes.

    Hate to interject some backyard engineering here but let's play devil's advocate and say there's a possibility of the HC failing under stress in the wood. What prevents one from applying a couple of drops of water thin CA along the HC and running with it? I don't for a minute think they won't work. The rhomboid shape and depth of the insert are plenty to maintain the force x 4 needed for a bass neck. I've only got anecdotal evidence to support that idea and that would be the successful use of NO insert or helicoil and just using a machine screw by some high end builders. Would using a helicoil be a gain or a loss over that method? Common sense answers that one. I can also state with some degree of certainty that top quality machine shops do indeed use helicoils in the right applications as I have discussed their use with some top notch builders during my racing operations back when.

    I'm not defending the use of a helicoil in this application. What I AM saying is that there's ample evidence - both empirical and anecdotal - to support the hypothesis that not only would it work, it might work really well. There's also plenty of evidence to warrant completion of the testing without regarding unsupported "scientific" opinion.
     
  20. mcdade

    mcdade

    Sep 27, 2004
    London (UK)
    Hi There,

    How has the helicoil fixing come out,im a toolmaker by trade and I use helicoils quite a bit for fixings into aluminimum when there is a need for constant un-bolting.Due to the thread form on the helicoil,there could be problems with the helicoils pulling out of wood.Ive used standard thread inserts of wood cabinet and had good results.

    [​IMG]

    [​IMG]