In true newbie style (spoken from my own past newbie experience), you have asked a humongous question, with too many aspects to consider in a single thread.
However, if you undertake this, allow this experience to be a first try experiment, don't get too hard on yourself for only partial success, and it will be hugely educational.
The big picture is, that in recapping a bridge, you are trying to load the strung board with a certain amount of downbearing. That is, the strings deflect slightly up in their path from agraffe(or capo) to hitchpin. This upward deflection loads the board somewhat with downward force from the tension of the strings. This means that the appropriate height of the finished bridge will be defined by the plate height, the strings, and the amount of crown extant on the soundboard. In a vintage piano, the board may have no crown left, and may deflect to flat or negative crown under string load, so one must assess the board's capability before deciding how much to load it. Copying the existing bridge height is of only limited value in most rebuilding situations, as the structure of the board, and its ability to resist downbearing forces will be different now than they were when the piano was built.
Bridge pin slant of 18 deg is common and adequate. Front and back pin offsets should be kept minimal, 10-13 deg lateral deflection of the string over the cap.
The notches provide one simple task: they waste wood so the strings have clear access to the termination point at the pins. The center of the pin is the termination point. The edge of notch begins either centered on the pins or towards the back of the pin slightly. The notch itself, ie the chiseled away part's only task is to achieve string clearance. You can make it look pretty and obsess about even-ness of the woodworking, but functionally its just getting wood out of the way, so string excursion only contacts the bridge at the termination point(front pin). Sometimes, long bridges are beveled instead of notched, especially on very old or very cheap instruments. Forget what is there and why. The goal is to create pin terminations so that there are 3 identical speaking lengths for each unison. Then after creating those even speaking lengths, get excess wood out of the way, by chiseling (notching) away excess.
Pin fit is extremely important, meaning, the pins can't be too loose in the hole drilled in the cap. If they are not snug, there will be noises produced by the strings that cannot be tuned out. Loose pins sound real bad. Practice with varying size drill bits to get the angles close and holes consistent. You want the driven pins to present resistance to driving, but not so much that they bend. Put a dab of epoxy in each hole before driving the pin. Support the board from below while driving the pins. Use new bridge pins. Do not reuse the old ones...get them from Schaff, or other online supply houses.
Supply houses like Schaff sell the product Dag, which is the graphite. However, I don't use any graphite on my bridges. Europeans don't either. I'm not sure if it actually is a functional addition or just makes finding the termination edge with the chisel easier to see. If you can't procure the Dag, don't sweat it...there's other much bigger things to sweat in this first attempt.
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Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
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Original Message:
Sent: 06-03-2018 06:27
From: Abed Joud
Subject: Replacing Bridgecaps
Hello,
So I am restoring a 125 years old Anderson baby grand piano. I know it's not really that worth restoring, but I got it cheap enough that i am not super worried if I ruin it. The bridges on the piano are cracked up badly and I would like to replace them. I used a template to copy the curvature of the bridge into a new piece of 3/4" thick solid maple board. When I used my depth gauge and it looks like the left side of the treble bridge is a little thicker than the right side (about 1/8" thicker) My questions are:
1- is 3/4" enough for a new bridge cap?
2- The bridge pins are dislocated to the point that I may not be able to get the angle of the pin correctly, will that be a problem? I think I will drill all holes at about 45 degrees.
3- The notches in the bridge cap, are they all identical? Or is they of different width/depth (the ones on mine are notched in the beginning but they look like someone got bored and never completed them)
4- where would I be able to get the graphite to burnish the bridge cap?
I am a newbie trying to figure things out. And I appreciate all your help.
Thank you!!
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Abed Joud
Computer Engineer
Elk Grove CA
832-660-6502
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