The piano hammer is the single component that brings together all other aspects of piano construction. Without proper consideration, all preceding efforts to construct, or, in case of restoration reconstruct, a piano will be affected. Piano tone is not created but actuated and affected by the piano hammer head. Therefore, all other qualities of piano construction are dependent upon the piano hammer for the final resulting sound characteristics a piano will possess.
The piano hammer is the head of the action which travels towards the string to strike it into vibration. This phenomenon is what classifies the acoustic piano as a percussion instrument. The head is built with two primary materials: wood and felt. Both materials affect tone quality and performance.
The two parts of a piano hammer head are the hammer molding and the hammer felt. Moldings are generally made of hardwood such as maple, birch, mahogany, walnut, and hornbeam. These are the most common although other woods have been used. The felt is generally blended from wool taken from different parts of sheep and sorted according to fiber length (short and long) and fibers which are soft or crinkly. This allows for the felt to be carded and laid up according to the manufactures requirements.
Piano hammer making has evolved eclectically for the last 150+ years. Today there are several good choices for technicians when selecting new hammers for replacement. A tech must understand the nature of the instrument they are working on, know what the client desires, and choose the correct head accordingly.
That being said, the topic of this page will be on piano hammer head installation.
The Piano Hammer Replacement Process:
Piano hammers will need to be replaced for one or all of the following reasons:
- Different tone quality is desired
- Hammers heads are worn and/or damaged
- Hammers can no longer be voiced as desired
- Piano is being restored to like-new condition
New hammer heads as they arrive from Germany unbored with tails unshaped. Hammers are selected based on molding length and mass of felt. Typically, 15#, 17#, and 19# heads are used according to size of instrument. The bigger the piano the heavier the hammer. The weight refers to the weight of the piece of felt the hammers are made from, not the weight of the finished set. Size also varies within each set with heavier hammers in the bass and lighter, thinner hammers in the treble.
Hammer moldings are scribed for boring. Each head is bored at a specific angle according to positioning on the action, and at a diameter relative to the hammer shank they will be mounted on.
Precise measurements are taken to determine the correct flare angle in each section. Since the angles of the strings are not perpendicular to the hammer line the hammers need to be mounted at an angle. This is achieved by building in a graduated flare angle from bass to treble by drilling hammer heads accordingly.
Aside from the flare angle the head is drill at a right angle to the hammer shank in a grand piano. Vertical pianos are different due the angle at which the hammer approaches the string. These are typically drilled with a slight rake angle. Notice how the hammer being replaced has an incorrect angle.
- Test hammer marked to set up boring jig
- Measuring for the correct angle
- Noting that the head being replaced (not original, was previously replaced) is at an incorrect angle. This has a detrimental effect on action power, tone quality, and hammer longevity.
Hammer head getting drilled in boring jig. Hammer heads after boring.
After the heads are dilled the tails will be shaped according to the arch of the radius in which they move. Notice how the tails have a rough texture. This is how they arrive from the hammer maker. However, if used like this they will not geometrically match with the action. The tails must be shaped to have the correct radius. The idea of texturing is to create friction so the hammer will grip in the back check. However, this only serves to wear the back check leather prematurely. It is beneficial to build the correct radius into the molding so the back check and hammer molding match geometrically. This will leave the tail smooth and geometrically correct. Also, notice that the tails are tapered to remove mass and increase clearance. If a hammer head is excessively heavy it will not perform correctly. Hammer heads have tremendous tension at the striking point creating dynamics at strike and allowing rapid rebound. Making the hammer heavy (some actually will add weight to the head to regulate touch weight, a practice I do not agree with) makes the same difference as snapping someone with a gym towel or throwing it at them. The previous is far more dynamic.
Sanding the radius and tapper into the hammer head tail.Each is done individually.
Setting up guides at ends of each section. This will help position the installation jig correctly. The position of the guides is determined by the original hammer position checked against measurements taken within the instrument. It is imperative to get this correct else an improper striking point will be set, altering the intonation for the piano.
Hot glue is used to adhere the hammer heads to the hammer shanks. This typically is horse hide glue. The purpose of this type glue is twofold. 1) The glue can be heated to allow for future removal of the head without damaging the shank. 2) This type glue will not creep or pull the head when dying, insuring correct alignment.
Hammer heads after getting mounted to shanks. Notice how the excess hammer shank is removed and tails are sanded flush.
New hammer heads installed into action stack. Stack is now ready to be mounted to key frame and prepared for regulation.
Please remember that this, and all other technical information in this site, is not a DIY tutorail. Rather it is for reference and intended to inform our clients on our standards of practice.