widening nut grooves

Discussion in 'Setup & Repair [DB]' started by lin fung, Nov 14, 2002.

  1. lin fung

    lin fung Supporting Member

    Oct 9, 2002
    Taipei, Taiwan
    I just busted an E Eudoxa string while putting it on. That may have happened because the nut grooves are too narrow. I'd like to get the grooves widened, however if later I want to go back to using thinner strings will there be a problem? Will I have to get a new nut put on?

    Also, how can I know if the cause of the breakage is due the nut groove narrowness? How much of the string should be down in the groove and how much outside of it?
  2. You can widen it with a rattail file. Be careful that you only widen it and not make the grooves deeper. As long as you don't make the grooves deeper you won't have any problems with switching back to steel.

    You can tell if it's a problem with the nut if the string broke above it.
  3. Probably. That would be the best. Either that or have a shim fitted underneath the nut so that there is fresh ebony to profile the string slots.
    Grooves that are too narrow means that the string does not rest in the bottom of the slot and gets pinched on the sides, and can cause string breakage and problems with playability. Too wide and the string can buzz in this area.
    Examine the string closely to see if it got pinched in this area.
    I shoot for a groove depth of 1/2 string diameter.

    The groove needs to be carefully profiled and polished. It's depth should hold the string .25mm (.010") above the surface of the fingerboard. Ideally, there is a compound radius (toroid) shape to it. Sort of like the inside of a donut looking out.
    The radius that the string rests in should match the string radius closely (only slightly larger). The path of this groove should also define a smooth curve as the string breaks over the nut and angles its way to the pegbox. The highest point on this path should be the very edge of the nut where it joins the fingerboard otherwise the string can buzz and create intonation problems. The groove should be polished well and lubed with graphite. I soak them in mineral oil for a day, then clean the bottom surface with alcohol and glue them with weak hide glue.
    If you're not sure how to do this, get to a luthier. It will be cheaper than breaking Eudoxas.
  4. There are a few posts and short threads on TB talking about nut groove depth and width and how to (and not to) widen them and how strings should sit in them. The above comments by Pete and David seem to summarize most of the best of what's been said, plus Arnold's advice below.

    There are other comments too, and may be I haven't seen some of them. But there seems to be agreement that strings should sit well in the grooves -- on the bottom and not just over the top of the grooves -- at about one third to one half of their thickness, and their distance from the fingerboard ought to be a bout the thickness of "one or two business cards".

    I have two situations:

    Bass #1: steel strings (Belcanto/Spiro mix) sit well in the grooves and are at right distance from fingerboard, but the "shoulders" of the grooves for the G and D strings are too "high", i.e., nothing of the string sticks out of and above the nut.

    Question: Is it advisable to simply sand off the "shoulder" a bit to free up the string from the depth of the sides of the groove? Any problems encountered in doing that? Will the ebony show that 's been sanded and how would I get it smooth again?

    Bass #2: I got new (Gamut) gut strings, pretty fat, and clearly will not fit down into the grooves, especially the D (it's as fat as the E string of many sets I've had).

    Question: I'm worried about making the groove too wide and having trouble with a thinner D string later. If I file away just at the sides a little, is it OK to taper the groove's sides down so that the fat D will sit tight and close, but maybe not on the rock bottom, and this way a thinner string on the bottom would still have lateral support and not buzz? I guess I'm asking: Must the Gamut really sit absolutely all the way down in on the bottom? How much pinching can I risk?

    I'd appreciate any comments if you've had some experiences here...