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crosspost (severe back bow problem)

Discussion in 'Luthier's Corner' started by cosmicevan, Jun 20, 2003.


  1. cosmicevan

    cosmicevan

    Feb 1, 2003
    New York
    i apologize for the cross-post on the board (i've posted in setups, but i'm dying for an answer)...
    ------------
    greetings TBers...

    I'm working on fixing up a (Andy) Schack bass. Basically, the problem is that there is a severe back bow (to the point were an open string will not resonate at all). I've tried raising the string height and I've loosened the truss rod as much as possible, but the neck remains back-bowed. There is a zero fret on the bass so I'm guessing that a nut shim would be rather pointless?

    I've even tried clamping the neck with a straightedge to straighten it and left it for 24 hours...this didn't work. This afternoon, I tried clamping the neck to force it into an upbow and left it for several hours and this seemed to help a little bit but before I go and apply all sorts of pressure to the neck in various spots, I figured I'd check in with you guys to get some suggestions. The bass is at the shop where I work at for the weekend and I plan to resume work on monday when I have all of my tools. Can anyone offer up any advice on how to rid this bass of its back-bow problems?

    - someone commented on string tension as a possible problem and then i wrote...

    The string tension shouldn't really be an issue though. The bass was fine at one point...and then for some reason, the neck warped.

    I've been thinking about it and perhaps i could clamp it into an upbow with the rod rather loose and then tighten the rod to straighten out the neck and then add propper relief? I haven't figured out yet the best way to clamp it into an upbow though. I'm thinking that I can MacGuyver up some sort of rig where i have a level clamped to the center of the neck and then somehow add more pressure upwards towards the headstock with some clamps and some blocks of wood, but I'm affraid of destroying the neck.

    Also I've been thinking another idea could be to clamp the neck totally straight with the truss rod fairly tight and then try loosening the rod to add some relief? But again, I'm affraid of destroying the neck.

    What would anyone recommend (and please don't suggest bringing it in to a repairman...I use these forums so that I don't need to do that any longer). ANY and ALL help is more than appreciated...

    Thanks for reading and I eagerly await a reply!
     
  2. Nick Gann

    Nick Gann Talkbass' Tubist in Residence

    Mar 24, 2002
    Silver Spring, MD
    I thought that you would need to tighten the truss rod to take out back bow, not loosen it....
     
  3. cosmicevan

    cosmicevan

    Feb 1, 2003
    New York
    no, you tighten to straighten out an up-bow or remove relief. loosening will add relief and at times allow back-bowed necks to go straight.

    perhaps i should clear up the way i'm using the phrase back-bowed. i'm referring to a neck where the note will ring true if i push the neck up from the neck (not the fingerboard) near the headstock, meaning that the top of the neck is too low. the bass is neck through. thoughts?
     
  4. I'm sorry, but there are some problems that require professional help, or at the very least more thorough information than you can get from a few online posts.

    One of the things that's typically done to treat severe backbowing is "heat treating" the neck, where it's heated to a temperature high enough to loosen the glue holding the fretboard to the neck, then the neck is clamped with a jig to force the backbow out while the glue hardens again.

    A good repairman could do this, and would have the appropriate tools and jigs. Maybe you could do it, too, but you'd want to at least invest in a book or two on guitar repair, such as Irving Sloane's classic "Guitar Repair".

    Good luck!
    Mike
     
  5. cosmicevan

    cosmicevan

    Feb 1, 2003
    New York
    Thanks for the pointers Mike, but my goal here is to become a better repairman and I've invested quite a bit in books, videos, dvds, etc (dan erlewine is the man!)...and with no repair schools locally, I'm forced to do my work hands on as I study. I'll definitely look into Irving Sloane's book (and any others that you've found helpful...I have quite a few already) and please recommend whatever you can that is geared more for bass then guitar repair.

    And please keep the suggestions coming on fixing a neck in the shape I've described!

    Thanks!
     
  6. Heck, I didn't know you were already so far along the repairman route! I figured you were just an average schmo like me, used to doing typical setup stuff. :rolleyes:

    AFAIK, the Sloane book is sort of the "classic", but it's old enough that it doesn't cover some of the newer tools and materials, like the modern glues and whatnot. (Been a while since I looked at it, though...)

    I'm not aware of any repair books out there that are specifically bass related except the BP "setup guide" sorts of things, but most of the guitar stuff applies equally to bass.

    You probably already know way more than I do, but you might try over at the MIMF http://www.mimf.com if you haven't already been over there. Have you been over to FRETS.COM? They also have a nice set of pages on repair techniques at http://www.frets.com/FRETSPages/pagelist.html#Luthier. I didn't happen to spot anything on heating the neck to straighten it, though.

    Mike
     
  7. FBB Custom

    FBB Custom TalkBass Pro Commercial User

    Jan 26, 2002
    Maryland
    Owner: FBB Bass Works
    I would try clamping to the straightedge and applying heat. Distribute the heat as uniformly as you can, and obviously you'll want to avoid scorching the wood. Perhaps an electric blanket or a heating pad can get you there?