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.  

Construction has begun

After several months of study and design calculations, the drawings have been completed and building of the harpsichord has begun. Many thanks to Ernie Miller's answers to my many questions and his expert posts on the North Carolina's Woodworker site (Ernie's first part).

Following the practice of my internet mentor, I chose to build the keyplank first.  The keyplank is a flat board from which the individual keys are cut.  The keyplank shown above was made from edge-gluing 0.5 inch thick x 5.5 inch wide poplar boards purchased from Lowe's.  The instrument design calls for a compass of 51 notes (C to d''') with an octave span of 6.25 inches.  Plastic shopping bags under the plank kept it from sticking to the work table as the glue dried.

Figuring out the width of the keyplank is easy after deciding on the width of an octave.  The two traditional choices are 6 1/4 inch and 6 1/2 inch octave spans.  The length of the keyplank depends on several factors.  First, the builder can choose the length of the natural keys and the length of the sharps to suit the player's needs.  After choosing the playing lengths of the naturals and sharps, the key levers need to be long enough to span the thickness of the name batten, the name board, the wrest plank (or pin block) and the register gap or gaps.  My keyplank is about 14 1/2 inches long for a design having a single register.