Posts tagged formula
Indeed, friction is one of the piano technician’s worst nightmares. At best, the piano is a simple machine – you depress a key, it lifts a hammer to strike a string. At worst, it’s a complex mechanism where levers and joints are in contact all the time and each surface area is potential for friction to either be too loose or too great: too loose and the piano feels ‘warbly’ and too tight and it either doesn’t function properly or feels like you have to work too hard to compensate for the touch.
I learned this only a few years back but the formula for touch on a piano is relatively simple (operative word being ‘relatively’). There is a 5:1 ratio of hammer weight to key. What that means is, for every gram of weight at the hammer there is 5 grams at the keyboard. An average hammer weighs in at about 8 grams (multiply by 5 = 40 grams). So if average touch on a piano is 55 grams per key, where are the other 15 grams of resistance coming from?? Answer: friction.
Today i had the opportunity to redo key bushings on a fabulous grand piano owned by one of the best jazz musicians in the area. With a lot of playing (both from his own practice and from his students), the bushings around the contact points on the keys were completely worn making almost a ‘knocking’ feel from side to side. A bushing is nothing more than a substance used to reduce friction between two contact points. In pianos, bushings are almost exclusively made out of cloth (some people mistakenly call it felt but truly it is cloth – woven together). The cloth then allows the interaction of joints. Centre pins are made out of steel and they need to interact with wood. Without bushings these two hard substances would click and knock together. As well, friction can be taken up by cloth in varying degrees of thickness. So the cloth is the perfect substance for acting as the ‘spacer’ inbetween.
Next time you’re at a piano, test the bushings. Take one key and swivel it from side to side and see if you sense a knock or a thunk. This will tell you they need replacement. Simply steam out the old ones (see pictures) and glue in new ones and you’re good for years to come.