Keywell blocks

Since the keyboard is narrower than the space it fits into, the remaining space is taken up with a pair of keywell blocks plus a transposing block. The keywell blocks are shown below, glued up against the decorative front edges of the case:


In order to make sure the first and last keys don't rub against these blocks, 2 mm shims were glued to the left and right edges of the key frame:


The removable transposing block, shown below, allows the pitch of the instrument to be changed by shifting the keyboard sideways to fill the space left over when the block is removed. The block is held in place with two rare-earth magnets that are attracted to nail heads inside the keywell.


The keyboard shifts by one jack position, which allows a pitch of A=415 Hz when to the left and A=440 Hz when to the right.

Determining the proper thickness of the keywell blocks is an important part of making sure that the keyboard is properly aligned with the jacks: if not, the jacks could slip sideways off the key ends. I did this by progressively planing the blocks down and putting them in place, then sliding the keyboard left and right and observing how the jacks sat on the keys in both the left and right positions. When everything looked good, I glued the blocks in, then planed down the transposing block to fit the leftover space.

Keyboard: Balance pins, rack pins and mortises

Before unscrewing the key panel from the key frame, I transferred the actual locations of the rack slots back onto the ends of the keys with a thin knife blade and a straight edge:


Then I removed the key panel and drove the balance pins into the key frame. They need to protrude enough so that the thickness of the red balance pin felts and cardboard punchings underneath the keys, along with the keys themselves, is accounted for:


Also shown above is the green backrail cloth, which keeps the key ends from clacking against the key frame when they fall back.

Next, I transferred all the scribe marks on the key ends down the rear edge of the key panel, and then I drilled the rack pin holes using a spare rack pin as the drill bit:


This ensures a fit that is snug but not super-tight. I don't think there's any need to drill 0.1 mm undersize for these, as I have with other pins.

Keys are made to pivot up and down on the balance rail by elongating the balance pin holes into slots that have a triangular profile when visualized from the size. Each slot narrows from the top surface of the key down to the underside, where the original balance pin hole of 3/32" diameter is preserved. To make such a slot, this special mortise punch is used:


The tool is tapered from front to back but has parallel left and right sides, which keeps the slot of constant width (0.096", to match the balance pins). The tip has a rounded section that ensures the punch won't cut through the hole on the underside. This hole must be preserved so that the key won't shift back and forth as it moves up and down.

In use, the tool follows the balance pin hole drilled earlier and basically crushes aside the key material as it makes the triangular profile. Because no material is actually removed, apart from what is lost when the balance pin holes are drilled, the slot can be fine-tuned in future: if it's too tight it can be burnished with a spare balance pin, and if it's too loose it can be soaked with water or steamed over a kettle to swell the wood fibers. This approach is safer than trying to cut an exact slot, because once material is cut away it's gone for good.

I chucked the punch into the drill press (with the power off, of course) which gave me a handle to press the tool down as well as a way of keeping it square to the key panel:


The punch has a straight metal rod passing through it which acts as a visual aid in getting the punch sides parallel to the left and right edges of each key. Clamping the panel helps when withdrawing the punch from each mortise slot, as it tends to get jammed in there.

Key panel, key frame and miscellaneous details

I've been busy this past month with various concerts, so I've collected smaller bits of work I've done over the past little while into this single post.

Back in October I glued up the key panel, out of which the keyboard will be made. This consists of several 1/2" thick basswood boards 6.5" wide (the width of one octave) and of varying lengths to suit the 8-degree taper that the keyboard must have in order to fit inside the instrument. The key panel isn't a big deal at this early stage, but here's a picture anyway:


It still needs to be cut off straight (but at an 8-degree angle) along the back.

This will sit on the key frame, which is made of soft maple:


The key panel, when cut to size, will be almost flush with the front of the key frame and somewhat short of the back edge. At the back, the rack—that strip of maple sitting behind the key frame—will be glued on edge. This will have a series of vertical slots which will accept a metal pin driven into the end of each key. When the key is depressed, the pin and slot will ensure it moves straight up and and down.

The balance rail—the chamfered rail in the middle of the key frame—will be the pivot point for the keyboard. Each key will have a mortise punched most of the way through it from above, and a pin will pass through this mortise into the balance rail. This second guide point together with the rack will keep the keys moving vertically, without skewing sideways and touching their neighbours.

Back in mid-September, I visited A&M Wood Specialty again and selected a large plank of Alaska yellow cedar to use for the exterior casework of the harpsichord. I ended up with a board about 9 feet long, 10 inches wide and 1" thick (all rough dimensions). Since the moisture level of this board was a bit high, I purchased it and arranged to have A&M keep it for me until it dried out somewhat. By late November the board was ready to go, so I had A&M resaw and surface all the resulting pieces to my required final dimensions of 7.5" wide, 3/16" thick. They did an excellent job for an eminently reasonable fee of about $25. I ended up with 4 long resawn boards plus one thicker full-length piece that came from the original board when it was ripped to width. This will be used for mouldings, of which there are a great many on an Italian instrument.

Alaska cedar is a lovely wood of pale yellow colour and very subtle straight grain: it's quartered so the grain is quite even. It has an oddly herbal smell when freshly-cut, quite unlike the usual resinous evergreen fragrance. In fact it smells as if someone has been smoking pot somewhere nearby!

The case wood is thin, so the bentside can be made by simply shoving a board against the glue-smeared knees and clamping until the glue dries. Other sides are treated similarly, except that they need no bending. The numerous mouldings that go along the top and bottom edges of these boards will also strengthen them and keep them from being too floppy. A nice example—one of many in the Italian harpsichord tradition—of form and function being combined.

During the course of October and November, various items needed for the harpsichord arrived from various destinations: cloth padding of various types, boxwood plates which will make up the natural key covers, strips of ebony from which the sharps will come, maple arcades to decorate the front edge of each key, tuning pins, bridge pins, hitch pins, and so forth. I was lucky to have purchased all this stuff at a time when the Canadian dollar was skyrocketing to all-time highs against the US dollar. It also gained against the Euro, which helped offset the cost of buying things from Europe.

My sources are:

The Instrument Workshop: cloths, key covers and sharps, some specialty tools, plectra and strings.
Hubbard Harpsichords: maple arcades and specialty drill bits.
MicroMark: several small tools.
Marc Vogel oHG: brass and iron pins of all sorts, soundboard rose, soundboard wood.