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severe back bow problem

Discussion in 'Hardware, Setup & Repair [BG]' started by cosmicevan, Jun 20, 2003.


  1. cosmicevan

    cosmicevan

    Feb 1, 2003
    New York
    greetings TBers...

    I'm working on fixing up a 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 fr 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?

    Any and all help/suggestions are appreciated!

    Thanks!
    Evan
     
  2. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    Very heavy/high tension strings?
     
  3. cosmicevan

    cosmicevan

    Feb 1, 2003
    New York
    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 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...
     
  4. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Some details will help to come up with a fix.

    Is it a bolt on or neck through? What FB and neck material? Was the bass being stored in a case or leaned up in a corner when the warping occurred? Were the strings changed to a lighter guage prior to the prob showing up? Did the prob appear all at once or over a period of time? Have any frets just been replaced? Does the truss nut feel normal when you attempt to adjust it?

    You might try loosening the strings and placing a short piece of 3/4" to 1" dowel (or any kind of block) between the fingerboard and the strings at the last fret and bringing the strings up to tension. This will change the angle of the string tension and should induce a bow. Let the instrument set for day or two but check often enough that too much bow is not introduced.

    When adjusting the TR, hold some bow in the neck by holding the bass as you would when stringing an archery bow. Make sure that the TR nut has not bottomed out.

    Exactly how much back bow (measurement) is in the neck?

    Pkr2
     

  5. Ooooh! THAT is a neat suggestion! Simple, safe, and damn near foolproof.


    BTW Pkr2, You've got mail...
     
  6. cosmicevan

    cosmicevan

    Feb 1, 2003
    New York
    Hey Pkr2

    I'll try my best to anser your questions, but I don't have the bass in front of me.

    > Is it a bolt on or neck through?

    Neck through

    > What FB and neck material?

    I believe that it is an ebony board. The wood is virtually black, but I'll double check the specs on Monday.

    > Was the bass being stored in a case or leaned
    > up in a corner when the warping occurred?

    As far as I know, the bass lived on a guitar stand. It came in with no case and I never noticed it in a case. I realize that this may sound totally ridiculous, but how badly will that effect the neck? I know that gravity plays a big force on measurements if your instrument is not in playing position.

    > Were the strings changed to a lighter guage
    > prior to the prob showing up?

    The strings have not been changed.

    > Did the prob appear all at once or over a
    > period of time?

    My boss pointed out to me that there was a problem with the bass and when I looked at it, I saw the back bow. When plucking the string I got nothing...then when applying some downward pressure on the neck towards the headstock and plucking the string, the note rang true.

    > Have any frets just been replaced?

    All original frets

    > Does the truss nut feel normal when you attempt
    > to adjust it?

    As far as I can tell. The rod was not tight and I loosened it some and gave the neck a little help, but that didn't seem to do the job (I thought Andy Schack used dual action rods?).

    > You might try loosening the strings and placing > a short piece of 3/4" to 1" dowel (or any kind > of block) between the fingerboard and the
    > strings at the last fret and bringing the
    > strings up to tension. This will change the
    > angle of the string tension and should induce a
    > bow. Let the instrument set for day or two but
    > check often enough that too much bow is not
    > introduced.

    WOW! What a great idea! Have you tried this and seen it work or is this just some creative thinking?

    > When adjusting the TR, hold some bow in the
    > neck by holding the bass as you would when
    > stringing an archery bow. Make sure that the TR
    > nut has not bottomed out.

    Whenever I adjust a truss rod, I always help it out a bit, but in the case of getting rid of a back bow, one would loosen the rod correct? So bottoming out is definitely not an issue.

    > Exactly how much back bow (measurement) is in
    > the neck?

    I'll check on Monday. Let me know where the best place to take a measurement would be. What I can tell you is that any fretted note below around the 7th fret cannot be heard at all, so it is pretty bad. I also jacked the bridge height as high as I could and even that didn't help!

    Thanks so much for the suggestions and keep them coming...I'll be back at work on the bass starting Monday and I'll keep everyone posted on what works and what doesn't as I'm sure that this is a problem that can be found on other basses.
     
  7. cosmicevan

    cosmicevan

    Feb 1, 2003
    New York
    Update...Pkr2, you rock! Your idea worked like magic! It releived the backbow issues and even gave the neck a bit of relief. I let it stand for 2 days with tension set to pitch with a 1" dowel going across the fingerboard at the last fret.

    The bass can still use a bit more relief and since the truss rod was very loose, I decided to tighten it just to the point where it felt a bit tense and moved the dowel up a few frets to where the neck and body meet and then strung again to pitch. I'm going to let this stand for about 3/4 of a day and then check it in the morning and see. I figure if I have too much relief I can use the truss rod to tighten that out. But ideally it would be nice to keep the string height low but still having good action (I prefer my action primarily in neck relief and do my finer adjustments at the bridge).

    Please feel free to comment on my plan of attack, but I feel comfortable enough that this additional time with the wood dowel will not to anything to the neck that can't be fixed with a bit of tightening on the truss rod.

    Thanks again for all of your help! This site is incredible and your advice prompted me to become a supporting member! Look forward to seeing all you supporters in the Lounge!
     
  8. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Glad it worked well for you. You probably will get a more accurate relief by moving the dowel to around the fifth fret. Use caution with trying to do more than just straighten a neck with this method because you can easily overbend the neck.

    Ideally the relief should be in only the first 5 or 6 frets. From frets 5 or 6 to the end of the finger board should be practically straight.

    Don't forget to snug the TR nut down so it doesn't rattle. I'll bet that in a few months it will be back in to have the action checked. Something is a little unstable about a neck that just suddenly assumes a back bow for no obvious reason.

    Good luck.

    Pkr2
     
  9. cosmicevan

    cosmicevan

    Feb 1, 2003
    New York
    well, the bass was actually just not given propper care and the neck was forced into a backbow by being leaned on a coach for too long a period. moving the dowell up a few frets really gave the neck a nice bow which i can easily straighten out and give propper relief and action to. Thanks again for the great idea!
     
  10. i got my neck heat pressed and the frets filed for 50 bucks. i got it done by paul munden he sets up alot of guitars.