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bridge fitting

Discussion in 'Setup & Repair [DB]' started by pkr2, Mar 10, 2002.


  1. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    I've found that fitting the bridge feet to the compound curve of the top to be aggravating as the devil.

    Is there a jig, a tool or a method to ensure that the bridge is perpindicular to the top? I know that the joint between the top and the rib is the reference line but there must be a better way than just eyeballing it.

    I have always put a cavity in each foot, leaving about a quarter inch of material around the perimeter of the foot bottom to cut back on the amount of material that must be removed from the feet.

    Am I inviting sound post damage by using this method? It has just occurred that the bridge end of the post may not be supported properly with my method.

    One more question. I'm on a roll. :)

    Should the bridge be centered on an imaginary line between the F hole notches, or should either the front or back of the bridge be on that line?

    If the way my questions are worded are confusing, just let me know and I'll probably make them a lot more confusing.

    I would especially appreciate any input from our resident luthier, Jeff Bollbach.

    By the way, Jeff, you are a very welcome addition to the DB forums. A belated welcome to you.

    Pkr2
     
  2. Jeff Bollbach

    Jeff Bollbach Jeff Bollbach Luthier, Inc.

    Dec 12, 2001
    freeport, ny
    That pkr2 could be anything-you are not giving us any clues, not even a locale. For all I know you could be in an Afghani cave. I don't give out free luthier advice to Al Quaida! Throw us a bone in your profile![and also consider the contentment of being a supporting member]

    I don't think there is much risk in terms of the foot not fitting in the way you describe. Just as long as it is not standing on an edge-but there could be some impact on the tone. I would reccommend to try to get at least an 80-90 percent fit. I'll describe how I fit mine-mebbe that will help. I know of no jig that will help you in the angle of the bridge. You should be able to see that by eye though. It may help to orient the bass as parallel to the floor as possible and eyeballing the corners and interior blocks may help. These are usually perpendicular to the flat plane of the plates.
    The feet should fit on the imaginary line between the inside f notches with it bisecting them. This can be varied somewhat in the interest of changing the string length-but that is not really desirable. Draw the line with a china marker, but be very careful to apply very little pressure as it may indent the varnish. This can be removed later with mineral spirit. Outline the feet as well. At this point I fill in these outlines with lipstick. This works very well in showing where the foot is fitting and where it is not. The only real drawback to using lipstick is that anyone witnessing you using it will feel compelled to challenge your masculinity[if you are male]. The shade is not crucial but a flaming red is most visible.[I am very secure in my sexuality] Now, the tool you use to fit the feet is crucial. Some use sandpaper but this is amatuerish and it does not yield a fine result. The best tool is a very sharp slightly curved knife. A curved scraper can also be used. Just keep at it-this is a job that requires some patience.
    I hope this helps, but if you have any more questions feel free to ask.
     
  3. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Thanks for the response, Jeff.

    Sorry about the missing profile. At one time it was filled out but I haven't looked at it in a long time.

    It's now taken care of.

    The reason I chose Pkr2 was because I didn't think there was any possible way that Ed could butcher a name like that. I was wrong! :) j/k Ed.

    Great idea with the lipstick thing. I do kind of the same thing but I use a charcoal pencil as the transfer medium. I'm sure lipstick would show up better.

    I'll try the knife/scraper thing. I have to admit I've always used sandpaper.

    Pkr2
     
  4. Johnny L

    Johnny L

    Feb 14, 2002
    Victoria, TX
    I purchased a jig from Stewart Mcdonald that was originally intended, I think, to be used for violin bridge feet fitting. I modified it a little to hold the feet of my adjustable bass bridge square and did the sandpaper trick on it. Amateurish it may be, but I managed to get the feet to stand flush against the top with a 90 degree angle between the top and the back of the bridge without a single swipe of lipstick, charcoal pencil or china marker. The bridge feet are centered across the f-hole notches and give me a string length of exactly 42" on my Strunal.

    Just like Jeff Bollbach said, the jig didn't do squat for me on the angle. I had to achieve that the hard way.

    I've read some violin repair books at my local library that endorse this jig-sandpaper method over the knife method on feet fitting, but Bob Gollihur has a link to an indepth treatment (with illustrations) on this kind of work Jeff's way sans lipstick.
     
  5. rkmullen

    rkmullen rkmullen ricks repairs

    Jun 18, 2006
    Dutchess County, NY
    I
     
  6. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    Rob Wilson showed me a similar jig he made. I think he still finishes by scraping.
     
  7. eh_train

    eh_train Supporting Member

    Jan 12, 2004
    Toronto
    Hi RKMullen,

    I'd be very interested to see your pics. Other TBers may be as well - If it's not too much trouble, could you post them to this thread? If it's difficult or not something you want to distribute widely, please email me with info...

    Thanks!
    Paul (Eh_train)
     
  8. rkmullen

    rkmullen rkmullen ricks repairs

    Jun 18, 2006
    Dutchess County, NY
    I
     
  9. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    Brewster, NY, USA
    How does sandpaper work on a bass top where the surface is not on the same plane under both feet? Almost every bass has some deformation there, so how can you get a good fit rubbing the bridge back and forth over sandpaper? Answer: you can't.
     
  10. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    I'm certainly no expert, but my observations suggest that it seems to help speed up the process as an interim step between bandsawing- which is good for removing bulk- and scraping.
     
  11. rkmullen

    rkmullen rkmullen ricks repairs

    Jun 18, 2006
    Dutchess County, NY
    W
     
  12. uptonbass

    uptonbass Proprietor, Upton Bass String Instrument Co.

    Oct 8, 2002
    Mystic CT
    Founder UptonBass.com
    oooof....sharp knives not sandpaper
     
  13. uptonbass

    uptonbass Proprietor, Upton Bass String Instrument Co.

    Oct 8, 2002
    Mystic CT
    Founder UptonBass.com
    AND carbon paper
     
  14. tsolo

    tsolo

    Aug 24, 2002
    Ft. Worth
    gotta admit there is a d*&^ fine fit between the bass top and the bridge feet on my Hawkes from Upton.
     
  15. rkmullen

    rkmullen rkmullen ricks repairs

    Jun 18, 2006
    Dutchess County, NY
    Y
     
  16. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    Brewster, NY, USA
    This is best done with a cutting tool (knife or gouge or chisel) and transfer material, such as lipstick, grease pencil or carbon paper. This way the bridge is merely set down in its proper place, some pressure applied, and the high spots reveal themselves to be taken down. With sandpaper you have to move the bridge around quite a bit which rounds over the feet or at least makes the fit inaccurate (especially where there is top deformation--90% of basses IMHO). BTW, luthiers are aware of this, but it's important for anyone trying their own bridge-fitting: make sure the soundpost is in place when fitting a bridge!
     
  17. rkmullen

    rkmullen rkmullen ricks repairs

    Jun 18, 2006
    Dutchess County, NY
    bridge jig
     

    Attached Files:

  18. Zachary Martin

    Zachary Martin Fine doublebass repairs

    Coming in a bit late in the game but...The bridge should have about a degree of back tilt toward the lower block. Save youself the headache and feet the feet before you install adjusters.
     
  19. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    Brewster, NY, USA
    Isn't this a bit too absolute?
     
  20. uptonbass

    uptonbass Proprietor, Upton Bass String Instrument Co.

    Oct 8, 2002
    Mystic CT
    Founder UptonBass.com
    and hardly the issue at hand....