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notch inserts (bridge) ??

Discussion in 'Setup & Repair [DB]' started by rod welch, Oct 23, 2009.


  1. rod welch

    rod welch

    Sep 13, 2006
    Finland
    HI, I'm not really up with the terminology and I've been searching the forums but can't find much info...
    I've got a 1/2 size bass with buzzing 'cos too low action to repair. ("A" string mostly) Not done much work on basses, normally cellos and violins.

    The bridge seems too good to dump so was thinking about putting in some "inserts"... what about using ebony??

    ...and then making a new top nut as it seems flush with the fingerboard... was wondering about top nut clearance??

    They want the action low as possible... at the moment it's on 8 and 5mm... was thinking I'll try to get away with 9 and 6mm

    Any thoughts??

    Thanks rod finland
     
  2. That sounds like the problem is really the shape of the fingerboard or the bridge position rather than anything else... 8 and 5 mm sounds about right for a 1/2 size, and the nut should put the strings maybe 0.2 mm at the most off the fingerboard. If it has a fingerboard bevel, it could just be that the bridge is a few mm off center to the E string side, that would make the A buzz.
     

  3. There should be clearance just the thickness of a heavy business card at the nut. The only buzz a low nut can cause is on open strings.

    If the bridge is too low but in good shape otherwise you can add adjusters (recommended) or you can add wood shims under the feet of the bridge. To temporary test a higher bridge try shimming under the feet with chunks of credit card. Of course loosen the strings some to lift it.
     
  4. rod welch

    rod welch

    Sep 13, 2006
    Finland
    Thanks for the advice...
    Yes, the bridge was quite over towards the E side... yes there is a bevel...

    of course... thank you...

    Having realigned the bridge and had the strings off to look at the topnut, I have the A string right through the nut onto the fingerboard and now an action of about 6.75 on the E, 6 on A, 7.25 on D, and 6 on the G.
    There is a hump on the fingerboard on the bass side where it leaves the neck which moves progressively up the f.b as you move across to the treble side...
    Also seems to be a flat around the bottom end of the G string...

    It's used with classical bowing for the most part...
    So, what I was thinking... new topnut, put an insert on the E and the A, reprofile the bridge and shoot the f.b. to form.
    Can anyone tell me what the optimum f.b. concavity should be?
    Is the concavity along the bevel similar to the rest of the f.b.? (i.e. half-way point of the string etc?)
    ... and, what is the radius of the f.b profile?

    Don't want to offend anyone, but I wouldn't want to put shims under the bridge... if it was mine maybe, for a quick fix... was thinking about that too... maybe spruce would be good for the shims rather than maple as it would really conform to the feet of the bridge and the top... Bit of endgrain perhaps???

    Thanks...
     
  5. No problem. I didn't notice it was not your bass and you are experienced with string repair. I don't put shims under the bridge either but is an accepted practice by some. If you do, plane the feet flat, so you can glue on a matching shim (not end grain) and then refit the new foot surface to match the top. Then the height will probably have to be fine-tuned by re-notching the string grooves. A good deal of work here.

    Adjusters are a better modification, I think. At less than $20 a set they provide added utility and some say they actually improve the tone. With a drill press you can install them rather easily. You will also need a tap and drill (Lowes) to match the adjuster thread. Search this forum for specific instructions.

    Maybe one of the resident Luthiers can help with your fb planing question and maybe comment on the string inserts.
     
  6. Pentabass

    Pentabass

    Dec 11, 2007
    Winnipeg
    You would likely experience wide fluctuations between summer and winter humidity in Finland, and therefore adjusters are an elegant way of dealing with seasonal changes in humidity and the effects on the string-fingerboard measurements, at the same time enabling you to raise the bridge now.

    Various answers to your question about the ideal scoop might be found in the archives of this forum.
     
  7. rod welch

    rod welch

    Sep 13, 2006
    Finland
    Thanks...

    I have been digging around the archives for what seems hours...
    The closest I came to some kind of measurement was "the thickness of the string at the point of greatest deflection..."
    Cannot remember where I found that.
    I did find some profile radius measurements though, so that's a good start.

    What I am looking for now is 4 basic measurements... (if anyone can provide... )

    Length of fingerboard.
    String height at end of the fingerboard.
    String height at the point of greatest concavity and the distance this point is from the top nut.
    (on the E and the G...)

    This will give me something to go on and I can work out some averages

    It's a conservatory instrument so I'll suggest the adjusters to the school. (and then some of you guys can point me in the right direction to find some... and the bits I need to fit them...)

    Yes, we get huge fluctuations of humidity and temperature. Drives me nuts, I've had violin fb's curl up and almost touch the strings before now. I've got a lovely old Ibanez Lonestar that you can only play above the 10th fret during the winter...

    Yes, grafting new feet onto the bridge is an option I suppose, but once I get the fb. sorted out, I might be able to get away with a single insert.. We'll see... Was thinking about an ivory/ebony/ivory laminate as an insert or do you think it will be too bright??

    Sadly, there is no Lowes, Home Depot, or any of the other incredible choices and resources that you have in the states, over here... :bawl:
     
  8. My adjusters needed a 1/4" imperial thread tap - quite common and easy to get a tap for that (I thnk that is a fairly common adjuster thread for metal (possibly not wooden) adjusters). I drilled my aluminium adjusters to reduce mass (and therefore reduce damping effect). The lighter the better. There are unfavourable comments about brass adjusters (heavy), but then everyones opinion differs and I have not tried them.

    I read somewhere that the fingerboard scoop should be as deep as the string overlying it - ie little on the G side, and a bit more on the E side. Can check by stopping the string at the end of the fingerboard and looking at the gap with a bright light on the other side. I'm sure someone will correct me if I'm wrong.
     
  9. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    What about using maple? Ebony will look weird.

    What about packing the nut up with a piece of veneer? IMO that's a respectable and invisible fix if done neatly. Same with packing up the feet with veneer, if its done well, and the feet properly fitted to the top, it can be perfectly functional and scarcely visible, if you're after a budget repair.
     
  10. rod welch

    rod welch

    Sep 13, 2006
    Finland
    Thanks Sjd, like the idea of the wooden ones....think there is a huge amount of discussion on the forum about them. I'll get into that when the time comes...

    Hi Matthew... Like I said before, If it was mine, shims and bits and pieces 'til I got the time to fix it properly, would be fine... not looking for a budget repair.
    I normally work on Violins and Cellos... Basses are a different animal but I think I would still prefer to replace things like nuts, etc. rather than mess around trying to fix them. Bridges on the other hand are worth conserving if they are in good nick..

    Ebony/Maple:
    Black and white wood together is cool... doesn't look weird?? :D (anyway, more concerned about wearing and tone than looks....)
     
  11. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    I still think it'd look weird, but whatever cooks your goose ... From what you say it sounds to me like the fingerboard needs more work than the bridge or the nut anyway.
     
  12. rod welch

    rod welch

    Sep 13, 2006
    Finland
    Yeah, that's why I'm trying to find some numbers of concavity...

    Length of fingerboard.
    String height at end of the fingerboard.
    String height at the point of greatest concavity and the distance this point is from the top nut.
    (on the E and the G...)
     
  13. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    no-one can give you those numbers just like that.

    For starters, its a bass, it doesn't work like a violin, there are no strict rules.

    Its a half size bass. So what is the string length? There's no rule. You usually need to allow for a high C, so THAT will give you your FB length. But you don't HAVE to make it that long. Some only go up to high B. And some soloists like even more.

    String heights are all relative to the amount scoop you put in the board, and that depends on the player, playing style, and to an extent the choice of strings etc etc. But, as has already been said, start by leaving a scoop depth of a string thickness under each string, with maximum scoop somewhere around the octave.

    I usually start by shaping the fingerboard, then cut the bridge crown to suit ... not the other way around.

    I treat the bevel the same as I do any other part of the board.
     
  14. rod welch

    rod welch

    Sep 13, 2006
    Finland
    Yes, exactly... so if someone gave me the numbers they are playing on, I could proportionally work around them and see what could possibly be used on this bass... Helpful to know what ballpark I'm in...
    (BTW "scoop"/fb.profile etc. on a violin also depends on strings/player etc. But I digress... )

    Not too interested in string length as that is so relative, but fingerboard length re: stringheight/concavity etc...

    Yeah, I would too....
     
  15. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    i don't think you understood my post. String length IS important, because the FB length is PROPORTIONAL to that measurement. If I give you the FB length of a bass in my workshop, 88cm, and another bass, 85cm, what will that tell you about your 1/2 size bass?

    ... my comment on the order of things was because you wrote
     
  16. rod welch

    rod welch

    Sep 13, 2006
    Finland
    Sorry... syntax has never been my forte.

    OK, thanks... that is one of the measurements I have asked about... Now all I need is the other three, on those fingerboards... That will tell me your optimum set up on those instruments... I can use those figures, proportionally adjusted, to compare to the configuration on my bass... jne.
    If I had all the data from say, twenty different instruments, I could find the parameters... it's all about analytic geometry.
    Once I had done that, I could look at all the figures, compare them, think f*** it, and do it my way anyway... But I would like to see the numbers first...

    So just humor me....
    (unless, of course, these figures are confidential... )
     

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