Cutting Apart the Key Levers

The keyboard plank is prepared for cutting apart by making a 3/4 inch wide by 5/16 inch deep rabbet along the rear of the keyboard plank.  The thinner section helps prevent the rear of the key from binding as it slides up and down on the rear guide pin

The keys are cut apart by starting with the lines between the B and C keys.  The lines between the B and C keys and the E and F keys extend the full length of the key plank.  A band saw is often used to make the cuts freehand.  As an alternative, a Bosch jig saw with a 0.03 inch thick blade was guided using two pieces of straight edged hardwood to guide the saw.  A scrap piece of lumber placed underneath the keyboard plank keeps the two halves in the same plane after the cut is finished.

The Bosch jig saw makes a thin, precise cut as seen in the following two images.

After cutting from front to rear on all the lines between B-C and E-F, the remaining cuts could not be made by clamping the straight-edged hardwood guides on both sides of the key.  I had finished making an adapter for the jig saw to allow using the E-Z Smart guide system designed for circular saws.  The following image shows the aluminum guide rail and the jig saw slipped into the base-plate.  One virtue of the E-Z Smart guide is that a fraction of a key width is sufficient to provide enough clamping area to hold the work to the bottom of the guide.  The threaded posts used in the clamps also serve as legs that hold the rail above the work table with the work clamped to the underside of the rail and enough clearance for the blade of the jig saw.

The next image show a close-up view of the blade cutting between G and A keys and the anti-chip edge of the guide.

After all the cuts are made the keys are still in groups of five and seven as shown in the following image.  A line 3/8 inch beyond the top of the naturals is drawn to mark waste area.  A hand scroll saw is used to cut the keys apart on a diagonal line between the existing cuts.  The hand jig saw is used to square off the final cuts.

The following image shows the keys after being cut apart and loosely laid out on the workbench.  The cut out between the sharps and the naturals will eventually be covered with the tops of the sharps.

A key lever mortise punch, a specially designed tool available at the Instrument Workshop, is used to enlarge the hole for the balance rail pins to allow the key to rock.  The tool is basically a triangular wedge of hardened steel with a cylindrical tip the diameter of the balance rail pin.  A little Caress bar soap rubbed on the punch makes it easy to pull out after being hammered into the wood.  If this is your first time make sure you practice on some scrap stock.  Also, be careful to align the punch to make a slot closely parallel to the long dimension of the key.  Here are the keys after placing on the balance rail pins showing the slot made with the punch.

The hole drilled at the back of the keys is used as a guide for making a slot of the same diameter.  The slot must be only a few thousands wider than the rear guide pin to prevent excessive sideways movement of the key without binding.  

The final images show the keys after placing them on their pins in the key frame.  A piece of scrap lumber is placed on the back of the keys to show them in their resting position.  (The short focal length camera lens added some distortion to what are actually evenly spaced keys).

Next step is to add tops to the sharps and decorate the top surfaces with a veneer.  I'm going to use solid Gaboon ebony for the tops of the sharps and boxwood to cover the naturals. 

Keyboard Pins

Pins 0.096 inch in diameter (from the Instrument Workshop) are tapped into holes in the balance rail and rear rail of the keyframe. The pins allow the keys to move up and down without sideways play. The holes for the pins are drilled using a 3/32 inch bit, which is slightly smaller than the pin itself to give a tight fit. I used a hand drill with a small block of oak pre-drilled to serve as a guide. To drill the holes, the keyboard is fixed to the keyframe using a few brads. The plan drawing shows where the holes are placed on the balance rail and the keyboard and keyframe are aligned before being temporarily attached. The picture below shows the holes for the balance rail after being drilled. Below the keyboard can be seen the balance rail, its bevel, and the alignment lines.

Another series of holes are drilled through the keyboard and into the back rail in a similar manner.  The following picture shows the scraps of wood placed under the keyboard to provide more stiffness when the holes are drilled.

Next step is to remove the keyboard, insert the pins into the keyframe, install some paper spacers around the balance pins and some felt on the back rail to silence the keys when the fall.

The next two figures show the block of oak 7/8 in. thick used as a guide to hammer in the balance rail pins and the complete key frame. 

The Keyboard Arcades

Arcades, a series of circular arches, are a traditional decoration on the front edge of the natural keys.  The arcades are easily made from one piece of trim attached to the keyboard plank before the keys are sawed apart.  The work starts with a piece of red oak stock purchased from Lowe's, 1/4 inch thick and 1 1/2 inch wide and 4 ft long.  One edge is verified or made straight and a parallel line is drawn 1/2 inch in from the edge.  This line marks what will be the bottom edge of the trim piece and the center-line of the circular holes to be drilled.  Lines perpendicular to the edge are drawn using the keyboard natural keys as a guide to match the spacing of the natural keys.  A series of holes are drilled using 5/8 inch and 3/8 inch Forstner bits.  A final hole is drilled using a 1/8 inch brad point bit to clean up the guide hole left from the Forstner bits.  The picture below shows three finished hole patterns after having been drilled with the final 1/8 inch bit.  The other hole patterns on the left show the small guide holes remaining to be drilled.

The piece is rough cut parallel to the edge slightly more than 1/2 inch in from the edge, just below the centers of the holes.  I chose to use a good hand held jig saw and blue painter's tape as a guide.  With a plane, the rough cut is made straight and parallel to the top edge.  The picture below shows the piece placed along the keyboard's front edge after planing.

The trim is glued to the front edge of the keyboard.  My mentor uses good ol' duct tape to clamp the piece.  My keyboard developed a slight warp after it was made, so several clamps and a spreader piece of scrap oak were used to hold it flat.  Some plastic was placed under the front of the keyboard to keep things from getting stuck to the work surface.  After applying glue to the back of the trim, the piece was clamped to the front edge of the keyboard.  The next picture shows the clamped arrangement.  (Notice at the left of the picture an experiment in using poplar to make the arcades.  The wood was found to be too soft to keep from tearing out when drilled with the Forstner bits.  Where have I heard that would happen?!).

Simulation

While waiting to get some power tools so wood cutting can resume, a computer simulation of the sound that the harpsichord would produce has been started.  The simulation is based on the physics of vibration.  Unlike a synthesized harpsichord sound that is adjusted to match the sound of a note played on a harpsichord, the simulation calculates the force transmitted to the bridge of the soundboard from each string when it is plucked.  The force the vibrating string exerts on the bridge is calculated as a function of time.  The force depends on several parameters that are entered for each string including the plucking point along the length of the string, the string diameter, the string density, and the tension on the string.  The vibrations of the string slowly decay due to the drag of air resistance.

The YouTube sound movie linked below was made assuming an infinitely stiff soundboard.  Eventually the simulated vibrations of the soundboard will be added to explore design choices for the bridge and stiffening ribs.  Headphones or high quality speakers are needed to capture the low frequencies.  See if you can hear the difference in the sound between a brass string and steel string, all due to the physics of vibration!

http://www.youtube.com/watch?v=H-MiuHUfDos