(from guest blogger Robert Furst)
THE PIANO ACTION & SCALE DESIGN
Briefly stated, the way a piano action works is that the down pressure on a key is converted to a forward motion of the hammer towards the strings. The hammer travels five times as far and approximately four times as fast as the front end of the key does, the key travel being only about 3/8 of an inch at its front edge. This is accomplished through a remarkable system of levers and pivots which, for a quality piano, must be adjusted to the utmost accuracy, making the action so responsive to the player’s touch on the keys that there is almost no limit to the musical effects obtainable. For a better, more natural leverage, piano keys slope slightly downward towards the back and become level when the key is depressed.
HOW A GRAND PIANO ACTION FUNCTIONS
Image by K. Wayne Land ©1998
A piano action would be a fairly simple mechanism if, when you depressed a key, it just had to push the hammer against the string. But if it worked that way, there would not be much tone because the hammer would stay against the string and, acting as a muffler, would stop it from vibrating. Thus, it would not have had time to return to its starting position after you released it.
If metal could be used, it would simplify the manufacturing problems and substantially reduce the cost; however, metal (not being noiseless without frequent lubrication and adjustment) does not lend itself to the purpose and very little of it is employed. Many other materials, including all kinds of synthetics, have been tried, but, with few exceptions, have not proved successful. Imagine a hinge or bearing that would work smoothly and silently for fifty years or more without lubrication or constant adjustment. Every pivot in a piano action must do this and they do it because these moving parts are held in a circle of specially made material called bushing cloth. Action hinges or pivots are made by boring holes in wooden parts, lining the holes with this bushing cloth, then connecting the adjoining parts with German Silver center pins which will rotate in these cloth bearings virtually without attrition unless exposed to the most abnormal climatic conditions. This cloth, among its many other properties, must be uniform in thickness to an unbelievable degree. The makers allow a tolerance of 2 one-thousandths of an inch, plus or minus, which is less than one-half the thickness of an ordinary business card and is an incredible measurement for such material. It requires a total of ninety-six different operations in the felt mill to produce the superior grades of this cloth used in actions.
Consider the manufacturing problem created by the fact that thousands of the parts in a piano are moving parts, that many are very small, and that, on some of them, a variation of a thousandth of an inch will affect their performance. Not only is the utmost precision required in making and assembling the parts, but they must operate quietly and resist friction, wear and loss of accuracy under long and strenuous use. The materials used today for the best piano actions are largely wood, felt, woolen bushing cloth, and leather. Like all products of nature, these items are inclined to be unstable when exposed to varying climatic conditions, although this hazard is greatly reduced in the better pianos by use of the highest quality materials and by superior workmanship.
To summarize the story about piano actions, good performance is not only a question of superior materials, but also involves skill, experience, and the willingness of the piano manufacturer to spend the extra money to have these important hidden parts as accurate and dependable as it is possible to make them.
THE QUALITY OF THE HAMMER:
This is another area where you can visibly see quality. Are the hammers nicely spaced? Are they all in line? Ask the salesperson about the hammer weight. Good pianos in a console size use about a ten to twelve pound hammer. Piano hammers are made of fine wool felt which is formed around a hard-maple hammer molding. First-grade piano hammers are made of two layers of felt; the outer layer is white, the inner usually purple, green or magenta.
The layers of felt are applied separately. The forming and gluing of the felt to the hammer is done with tremendous pressure applied by hammer presses. Many tons of pressure are applied from several angles, forming the shape of the hammers.
One of the least understood and most controversial subjects in the world of pianos is hammer weight. The prospective buyer is told that one piano has twelve-pound hammers, while another has only nine or ten-pound hammers. A glance into the piano tells us that surely those hammers, even all eighty-eight of them, do not weigh from nine to twelve pounds. The figure refers to the size of the felt sheets used in the making of the hammers. The felt in an individual hammer averages 109/1000ths of an ounce, depending on the weight of the sheet of felt from which it was made; and the difference between nine and twelve-pound hammers average 36/1000ths of an ounce per hammer. The important thing to remember about hammers, like all other parts of the piano, is that not only the quality of the materials, but how those materials are utilized in the building of the instrument determine the overall quality of the product. In the case of hammers, the proper shape and hardness are the key factors affecting proper tone regulation. That’s why it is often said that while a good hammer can’t make a poor piano sound good, a bad hammer can spoil the best piano.
Every musical effect in a piano must originate in the strings. The soundboard, no matter how perfect, can only amplify the sound produced by the strings. Pianos have from 215 to 230 steel strings graduated in length and thickness to produce the 88 notes of a piano’s scale design. The shortest string is about 2″, the longest string may be 84″ or longer.
• The bass strings should be pure copper wound, not plated.
• Examine the spacing of the strings in relation to other strings, spaced evenly without touching another string.
• Depressing a key slowly, check damper alignment. At the same time, check as hammer strikes the strings.
• Check to see if hammers strike all of the strings of all notes. Inspect the strings for even spacing (not touching another string) and proper alignment with the dampers.
• Listen to the piano – Is the tonal output powerful enough, at least impressive enough that you should expect from a “classic” piano, but capable, nevertheless, of filling a room no larger than 15 square feet or of a volume not more than say, 2500 cubic feet ?
• Is the tonal output reasonably mellow? (Very bright indicates hardened hammers from age or dry climatic conditions.)
• Is the tone even and with a fair singing quality ? Is the action satisfactory, that is, does it give a fairly elastic response to your touch ?
The proper weight for key depression is between two and three ounces, in general. Simply take a scale such as weight watchers, or the postage scale at the post office. Get a few weights (fishing tackle ok) and find a small weight that weighs around 2 1/2 to 3 ounces… place that weight on any piano keyboard where the fingers play and the key should depress. This is an accurate, but simple way to test for touch, the average touch is around 2½ ounces. (You can also get a weight watchers scale and weigh out several coins to make up 2½ ounces. Place them where the fingers would be.)
In the next part of this post, we’ll explore piano soundboards.
By Robert T. Furst, Author, Bluebook of Pianos and Piano Times
© 2011 Bluebook of Pianos
*Piano Times copyright used by agreement in the State of California.
Our thanks to guest blogger, Robert Furst. Visit his website—bluebookofpianos.com—for more information about pianos.