Building the Key Frame

The keyframe supports the individual keys, or key levers, and guides their motion.  The middle rail, made of oak, holds the balance pins that act as the pivot point for the keys to move up and down.  The middle rail's front edge is beveled to keep from interfering with the keys when they move downward.  Small discs of felt centered on the pins under the keys cushion their contact with the rail.  The back rail, made of poplar, holds another set of pins that prevent the keys from moving horizontally.  A strip of felt along the length of the back rail cushions the keys when they fall after being struck.

The following picture shows the middle and back rails (running horizontally) before installing the pins and the felt cushions.  The strips at the sides, called stiles, support the rails at their correct elevations.  The stiles are made of poplar also.

Shown below is a closer view of the middle rail's bevel.  I used a low angle jack plane to form the bevel.  The bevel has a depth of 1/8th inch at the front and extends towards the back of the rail for approximately 7/8th inch.

The keyframe's width is a fraction of an inch wider than the keyplank.  Shown below is the uncut keyplank resting on the keyframe.  Up until now the construction has used only hand tools (frame saw, chisels, and planes).  However, when cutting out the keys I need to use a band saw.

Several lines are drawn in pencil on the keyplank to outline the keys and locate the position of the balance pins and guide pins.  The next picture shows a closer view of a one-octave span on the keyplank.

The Plan

The instrument plan is based on 51 notes (C-d''') with a 6.25 inch octave spacing. All of the strings are brass with heavier, red brass in the foreshortened portion of the bass and higher strength yellow brass elsewhere.  An Iberian style harpsichord, such as the one made by Jose' Calisto c. 1780, represented a merging of ideas from Flemish and Italian construction.  Italian instruments of the seventeenth century were characterized by all brass strings and essentially Pythagorean length scaling (length inversely proportional to fundamental frequency).  The uniformity of string material and scaling produces a quality of evenness in the harmonic content of the sound.  Flemish instruments, such as those made by the Ruckers family, use a mix of brass and steel in the strings and have bass string lengths shorter than would be dictated by Pythagorean scaling.  The greater string tensions and multiple choirs required more robust case design and bracing.  The few Portuguese instruments remaining today combine Pythagorean scaling, all brass strings, and solid wall casing as in the Ruckers instruments.

The requirements for my experiment in construction were simplicity and ease of construction.  I found that the Ruckers style of case construction to be both simple and easy to produce.  I originally hoped to use Pythagorean scaling throughout the compass; however, the required overall length was judged to be unwieldy for a first attempt.  Thus, a somewhat unorthodox design resulted that can best be summarized as a either a foreshortened Portuguese design or an all-brass Ruckers.

The string plan is a single choir at 8' scale, keeping with the need for simplicity and the desire to keep the instrument at home for my own enjoyment.