How to Cut notches in your bridge or nut
by Bart Brashers
A nyckelharpa player writes:
I need to cut the grooves for some of my understrings a bit deeper – my bridge leaves the 6-set high enough that I can catch them ALL when I really go for the C-drone. Sounds… truly awful! Any suggestions as to the best way to approach this? Knife? Little saw? Razor blades?
I had that problem with my harpa, too. Mostly when I really ‘go for it’ and ask for some good oomph from the harpa. I dig deeper, and it pushes the playing strings down more which lets the bow touch the understrings.
A little saw is definitely the way to go. I went to a hobby store (or was it a hardware store) and puchased a few thin blades, but they turned out to be too thin. I think I just use a standard coping saw blade. The notch should be just barely wider than the string, and the strings are between 0.014 and 0.024 inches in diameter. So buying a saw blade that cuts a slot about 0.030 inches wide would be optimal.
To cut the notch, loosen the string a little and pick it up out of its groove. You can rest it on the bridge to one side, or drop it in another slot. Don’t use a handle (e.g. the coping saw handle – remove the blade) just hold it in your hands. I sometimes wear leather work gloves when I’m cutting a brand new slot, but you seldom need them when you’re just cutting an existing slot deeper. Check first to see that the blade you picked cuts the same width as the existing slot – it should not be skinnier. Hold the blade so it leans back (away from the keybox) just slightly. If it leans forward, then the string will rest only on the back end of the slot (the end closest to the tailpiece) and may buzz against the forward edge of the slot. You want it to be supported by the front edge of the slot, the edge of the bridge that does not face the tailpiece. I find it’s easier to hold the blade ‘backwards’ so the teeth cut when I pull rather than when I push. (This is the case for the carpenter’s tool ‘the Japanese saw’ – a smart idea.) Concentrate on guiding the saw blade along a straight line, so it cuts a straight slot. It usually only takes a few pulls to cut down deep enough. Remember, it’s far easier to stop early and have to cut away a little bit extra than to try to put some back!
And remember to blow away the sawdust before it gets into the body of your harpa. Sawdust absorbs a small amount of sound, and is simply unneccessary. And it makes your harpa look sloppy — notice how many people who really know instruments will look inside the body within the first minute of inspection?
Buzzing
Something to watch out for when you’re cutting either brand new or deeper notches in your bridge is buzzing. Or you may already have a buzzing resonance string, and you can’t figure out why — you’re pretty sure it’s not buzzing against the backs of the tangents or against anything else in the keybox.
If the groove or slot the resonance string lies in is too wide and slopes forward, then it could buzz against the sides or bottom of the groove. Basically, if the bottom of the notch slopes forward (as in the side-view scetch at right) then the string is supported by the back edge of the notch. This leaves a gap between the string and the front edge of the notch. If the distance is just right, it might buzz against the bottom-front edge of the notch, or against the sides of the notch.
Use a coping saw blade to cut the back edge of the slot a little deeper, making the slot to slope backward. You want the string to be supported by the front edge of the notch, so that the vibrating portion of the string is entirely within the area between the bridge and the nut. If the point of contact between the string and the wood of the brigde or nut is not the leading edge, then it could vibrate against that leading edge and lead to buzzing.
