Southern California Association of Violin MakersThe following article appeared in the November 1993 Bulletin. It describes a tool useful to violin makers, repairmen, and many musicians. The bridge jack, or string lifter, is used during final trimming of the bridge. Edward "Spike" Wolfensberger was president of SCAVM during 1987.
The materials for making a bridge jack are easily obtained and can be found in the scrap and junk boxes of almost anyone who makes things of wood. Five or six things are needed:
1. A rectangular block of wood, roughly 1.25 by 2.0 inches square and about 0.4 inches thick.
2. A scrap of leather, possibly from the tongue or sole of an old shoe, roughly 2.0 inches by 0.4 inches, and anywhere from one to three sixteenths of an inch thick.
3. A long threaded bolt or rod at least 2.25 inches long, with a minimum of 1.25 inches of thread. It can be either a number 8 or 10 bolt. If it has fine threads you will need a nut. Coarse threads are preferred because you won't have to turn the screw as many times when using it and coarse threads can be reliably used directly in the wood.
4. Two pieces of rod about an eighth of an inch in diameter. A long shank twist drill from a surplus store works well because it can be used to drill a hole that it will later fit.
5. A knob to fit the long bolt as a head to be manually turned. A knob about 0.75 inches in diameter is easy to hold, but it should be at least 0.4 inches to give some mechanical advantage.
The drawings included here are close to actual size. There are some rules that need to be followed. The drilling of holes in the wood is the toughest part because the drill tends to wander. The way to avoid that is to use a brad point drill, or, in the absence of that, to drill your holes using your drill press or drill jig with as close to the same setting as possible. A drill will drift in the same direction for successive holes in wood with the same setting. It is important that the guide rods are parallel to each other with a little misalignment permitted for the jack screw. The split between the upper and lower pieces should not be cut until the holes have been drilled. Determine where the lower radius will be and mark your drill, or set your drill press so that you won't drill through it. That curve should have a radius of 4 inches. After cutting off the lower piece, secure the guide rods in it and make a socket for the jack screw. Either tap and thread the wood or bury part of a nut in the lower side of the top piece.
The top should be formed to about a 2 or 3 inch radius (like the top of a violin bridge) with a few saw kerfs as shown to keep the strings from slipping off. Make sure the jack screw pocket has about 3/16 inch wood left beneath it, so it cannot break out, and then cover the bottom with a piece of leather to prevent scratches on the face of the instrument. Caution: do not use plastics or vinyl (Naugahyde) because the pasticizers in them can attack the finish.
Make sure the thickness is small enough to easily slip between the A and D strings. It is inserted at an angle (not vertical), then is turned at right angles to the strings, and then carefully stood up on the fingerboard side of the bridge. Turn the knob and the strings will lift from the bridge.
All Bulletin articles are copyrighted © 1997 by Southern California Association of Violin Makers. Contact Bulletin editor, John Gilson, at the address given on our home page, for permission to reproduce Bulletin material.
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