Key Lever Weighting

The balance pins and key frame support the key levers, which move like a playground teeter-totter or see-saw. Without being weighted, the keys tend to be front heavy. So the back of the keys require extra weight to ensure that they fall back down after being pressed. How much weight is needed to ensure they fall back down just right? After some research, I found that about 2.5 grams placed on the front of the key where a finger would normally press down during playing was good enough. Lead is added to the back of the keys to counter-balance the 2.5 gram weight on the front. A penny minted in the U.S. after 1985, which weighs exactly 2.5 grams, was placed on the front of the key. Lead cut from 1/4-inch diameter wire was shifted in position on the back of the key lever until the key was balanced. The lead poses a potential health risk, so gloves are a good choice for personal protection.

After marking the position of the weights in their correct position, 1/4-inch holes were drilled into the key levers. The typical width of the key lever is about 1/2-inch. The holes were drilled to a depth of 3/8-inch using a drill press with a 1/4-inch brad point drill bit. 

The lead often comes as a coil. When being cut to length, the lead has a tendency to deform. The deformity can cause the weight to resist being inserted into the hole. If there is too much resistance, the lead has a tendency to mushroom out at the top when being tapped down with a hammer. (The lead also has a tendency to oxidize quickly; so I keep the lead in a sealed plastic bag). 

One way I found of reshaping the weights back to perfectly round was to roll the piece of lead between two blocks of wood. The lead is soft enough to become perfectly round with only modest pressure applied during the rolling.

After 51 balancing acts, the keys are now properly weighted, I hope! 

Adding Key Coverings - Part 4

After successfully scoring the lines, the edges of the natural keys were rounded with sand paper. A four-way nail file with grit varying from 240 to 3000 (often available in an inexpensive 12 pack) proved to be useful for the rounding. A triangular file proved useful for refining the notch where the rounded edge meets the front decorative line.

After completing the wood surfacing, the keyboard is ready for weighting and leveling!

Adding Key Coverings - Part 3

The boxwood key coverings were flipped over and glued onto the key levers, again with hide glue. 

The decorative lines on the keys were carefully scored using a straightedge clamped to the keys. The X-Acto knife made straight, but very thin lines as before. This time, the lines were widened slightly using the tip of a thin screw driver blade instead of the Japanese saw. The screw driver blade acted somewhat like a mid-19th century American farm plow, which tracked the X-Acto lines easily and widened the lines as desired without slipping.

Adding Key Coverings - Part 2

The boxwood coverings for the natural keys were scored with a knife as a decoration to distract the eye from the joint formed between the front of the key and the skinnier back of the key between the sharps. Later, the side edges will be rounded as shown on the José Calisto harpsichord (Portugal, 1780) residing in the National Music Museum. In the photo of the Calisto harpsichord, the decorative lines are just visible toward the back of the head of each natural key.

http://collections.nmmusd.org/Keyboards/CalistoHarpsichord/CalistoHarpsichord.html

A straightedge was clamped to the keyboard to guide an X-Acto knife that was used to score the lines by hand. The technique worked relatively well, except that the X-Acto blade produced a line that was too thin to be seen easily. Real trouble began when I tried to use a very fine tooth Japanese-style saw to enhance the line. The photo below shows my attempt to score multiple keys at once using the saw held against a straight-edge clamped to the keys. On the third line, the straightedge slipped, resulting in an unacceptably crooked line.

Fortunately, the key coverings, which were bonded with hide glue, were able to be removed. The first attempt to remove the key covers was to bake the keys in an oven to raise the wood temperature to the melting point of the glue (about 145℉). Setting the oven to 250℉ did not get the wood hot enough for the glue to melt. Baking at a higher temperature was considered too risky, as the wood might start to smolder. So a second attempt at melting the glue was made by applying steam to the joint directly from the spout of a teapot using a towel wrapped around the key lever as a kind of steam box. Again, the glue bond would not get hot enough to melt. Finally, the key levers were immersed in water that was first heated to a boil and then poured into a glass jar, which itself was immersed in a heated pot also filled with water to keep the temperature from cooling off too fast. Usually, two minutes of soaking was enough to melt the hide glue. In some cases, a little mechanical impact with the tip of a screwdriver was needed to break the bond. Hide glue is strong stuff!

The image below shows the keyboard after the boxwood key covers were removed. In some places, the decorate arcade caps, which were bonded to the front edge of the keys using Tightbond yellow glue, did not survive the differential expansion that resulted when the two wood grains running in different directions absorbed water from the soaking.

Hopefully, the key coverings can be flipped over, re-glued, and re-scored with much cleaner lines.