Friday, October 17, 2008

Case moldings: Gluing technique

Here's how the cheek molding was glued on:


The little clamping blocks look like this:


They attach to the underside of the baseboard with two nails. First, each block was positioned with the dowel about half an inch from the case edge, and the nail at the block's midpoint was driven in. With the cheek molding positioned correctly, the block was rotated until the dowel pressed firmly against the molding, and then the nail at the opposite end of the block was driven in to hold the pressure and keep everything in place.

This setup should serve well for all the other pieces, and for me is preferable to clamping the molding with padded nails, which would leave behind unsightly holes. There are still nail holes using my technique but at least they'll be underneath the harpsichord where they will rarely be seen.

I have another clamp design in mind for the bentside molding, which may need some firm pressure at the cheek corner to make sure the curve conforms at its sharpest point. More on that soon.

Thursday, October 16, 2008

Case moldings: Baseboard level

Time at last to start applying moldings to the case. I'm starting with those around the perimeter of the case at baseboard level.

I made the moldings with one pass of a small router bit along both edges of the few remaining Alaska yellow cedar boards that I have left, then ripped strips about 17 mm wide off the boards. The width was chosen with two considerations in mind: first, this is about the maximum I could fit into my little miter box, which has a limited clearance between the business end of the saw blade and the bottom of the box; and second, the width has to be sufficient to hide all the screws that secure the bottom edges of the case to the baseboard.

Seen end-on, the molding has this profile:


Before applying the molding along the front of the instrument, I attached a filler strip in the keywell area so that the shelving on which the keyboard sits won't be visible. The strip also keeps the keyboard from sliding out of the instrument.


Although this strip looks like a solid chunk of yellow cedar, it's actually made of several thin pieces glued around a scrap of softwood. The molding will overlap it slightly and hide the brown baseboard edge completely.

I've prepared the first few pieces of molding in the rough: the cheek, bentside and tail moldings exist as over-length pieces, and the bentside piece has been steamed and is currently sitting in a bending form so that I won't have to wrestle it into the correct curve while trying to glue it down. In a day or two it will be ready to glue.

Friday, October 3, 2008

Keyboard: Completed

The keyboard is done.


After two coats of Danish oil, rubbed in between with extra-fine steel wool, and a light coat of wax, the keys have a lovely sheen and a silky-smooth feel under the fingers. The naturals have a golden glow and the sharps are dark and glossy. The scribe lines on the naturals have darkened and are more prominent now.

On to the case moldings now...

Tuesday, September 30, 2008

Keyboard: Applying finish

A view of the keys with one coat of Danish oil applied:


Even with just one coat, the keys have taken on a subtle sheen and the naturals have become more golden-coloured.

At least one more coat to go...

Monday, September 29, 2008

Keyboard: Keys rounded over

A good keyboard has all sharp wooden edges and corners eased to avoid discomfort. In addition, the front portions of the naturals have their edges and corners noticeably rounded over: this is partly cosmetic, but I think it also protects the fingers when the hands skim along the keys during performance.

I eased both naturals and accidentals with 600-grit sandpaper; a few swipes were usually enough to do the job. To round over the front parts of the naturals, I used 320-grit paper and sanded up to the first scribe line, holding a razor blade on edge in the line to keep from sanding too far back:


This rounding-over provides some nice shadow lines, in addition to being comfortable under the fingers.

The only thing left to do now is apply finish to the keys. I plan to use two coats of a clear Danish oil (an oil/varnish blend), followed by a light application of paste wax. Perhaps at some point in the future this might need to be re-done when the keys wear, but reapplying an oil finish is not at all difficult. Polyurethane is to be avoided on keyboards, as I've heard it wears off irregularly and looks awful after a while.

Keyboard: Details

Some further work on the keyboard:

Behind each sharp, I stained the top surface of the key lever black with an ebony stain for about a half-inch. This is a purely cosmetic detail often found on instruments with dark-coloured accidentals, and makes the sharp seem to blend into the back of the key. I did not stain any part of the key that is hidden behind the nameboard.

Each rack slot was rubbed with a very soft 6B graphite pencil to lubricate the slot and reduce any rubbing noises when the keys are played. The one minor defect in the rack guide design is that the slots run perpendicular to the grain: hence the rack pins bear on severed end grain fibers, which are a little rough. Fortunately the noise is usually covered by the music.

The stand, stained and finished

To take advantage of a recent stretch of good weather, I took the stand outdoors and, with my mother's help, applied stain and finish:


The legs and stretchers were first treated with a wood conditioner to minimize blotching, which maple can be prone to. Then two coats of a dark walnut gel stain were applied. When the stain was dry, four coats of satin finish (some kind of lacquer in aerosol form) were sprayed on and the final coat lightly rubbed with 0000 steel wool.

Now the interior moldings and the legs are a pretty decent colour match. I plan to make the music desk out of maple and finish it the exact same way.

Saturday, September 6, 2008

Keyboard: Levelling keys

After correcting unwanted tilt and unsightly gaps, the final cosmetic adjustment to the key positions is to ensure the rows of naturals and sharps are each at a consistent horizontal level. This is accomplished with paper shims of various thicknesses, which are placed under the red balance pin felt that insulates each key from the key frame.

I did this levelling strictly by eye. Usually a proper levelling is assisted with a thread stretched along the key fronts as a guide, but for now here's the result using my good old-fashioned eyeballs:


Levelling must take place after balancing, because the keys might not fall back properly until balanced and this could affect the level of the front edges.

The quantity of shims together with the thickness of the red head stop cloth under the key fronts gives a depth of touch of 1/4", which is typical for an Italian harpsichord. Maximum depth is determined by the sharps: if they are level with the naturals when depressed, the touch is too deep and extra notes might get played by mistake. On an instrument with two rows of jacks, the minimum depth must be enough for both rows to play successfully, as they pluck one after the other and not simultaneously.

I may have to repeat the levelling process in future, when the instrument is finally playing and the various action felts start getting compressed.

Keyboard: Balancing keys

Each key on the keyboard needs to be balanced so that it falls back reliably when played and released. This is accomplished either by lightening the portion of the key in front of the balance rail, or by weighting the portion behind the balance rail, or sometimes a combination of both.

French harpsichords usually employ the first approach, undercutting the undersides of the playing portions of the keys quite a bit to eliminate as much forward weight as practical. This approach can be used on other instruments as well. Since my keyboard is made of basswood, instead of a hardwood like beech or chestnut more typical of the Italian harpsichord-making tradition, I elected to balance my keys by weighting, which I think may also give them the slightly heavier feel of hardwood key levers.

By balancing my keys individually on a thin slip of wood, I found all of them to be front-heavy: not surprising, given that these keys are on the short side as a result of the Trasuntino's significantly angled gap and smallish wrestplank depth. I elected to use two sizes of weights: one 6 mm wide and 4 mm long, the other 1/4" wide and about 7/16" long, the latter cut by hand from a lead wire several feet long.

First I drilled holes 9/32" in diameter for the large weights, as far back as I could without getting too close to the rack pin:


This took care of the coarse balancing and made the keys back-heavy.

To complete the balancing, I placed a U.S. penny (weight 2.500 g) at the front edge of each sharp and centred on the scribe lines of each natural. This added weight at the front and tipped each key forward again. I then put a small weight on the key and started shifting it backward very slowly until the key just tipped back, as shown below:


I marked the final position of the small weight and drilled a hole for it. A few keys needed more than one small weight, but in the end all were balanced.

Balancing with a temporary weight in front gives a little extra reliability to the return of the keys when released, which will be assisted further by the weight of two jacks resting on their far ends. Some say that this method of balancing also reduces the possibility of an accidental brush of a key triggering an unwanted note, since the keys will require deliberate pressure to respond.

Keyboard: Easing keys

The balance pin holes and mortises are all a little snug at present and the keys need to move as freely as possible without actually being loose, so all the mortises and holes need to be eased to reduce friction.

I used this tapered reamer, which reaches a diameter of 3/32" (matching the balance pins) roughly at its midpoint:


A reamer is a cutting tool and I have previously stated that it isn't a good idea to cut material away when easing keys, in case one goes too far and needs to undo the adjustment. I tried to press the reamer into the balance pin hole from below without twisting it, which would bring the cutting flutes into play. To ease the mortise portion, I put each key onto the leftmost balance pin of the key frame (as shown above) and worked it up and down firmly, letting the pin burnish the mortise sides.

What I'm aiming for is to be able to lift each key straight up on the balance pin and have it slide back down on its own when released. That strikes a good balance between looseness and tightness.

Keyboard: Gluing on sharps

With tilted keys and uneven gaps between keys now corrected, it's time to glue the sharps on.

First I needed to make sure of the final lengths of the sharps to ensure their back ends wouldn't collide with the nameboard when the keyboard was in place. Until now there has been no nameboard, so I went ahead and made one, set the keyboard into the instrument and slid the new nameboard into place. The point was to check whether the front layout line drawn on the key panel (still visible on the sharp levers) aligned with the front face of the nameboard. It did, so I was able to establish a final sharp length, cut the necessary quantity of sharps from my ebony sticks and bevel the front of each sharp at the strip sander to a 10 degree angle.

Next, a straightedge was clamped along the final position of the sharp fronts, leaving a clearance of 1 mm between the naturals and sharps. With a flashlight shining up from underneath the key frame, each ebony sharp was visually centred in the gap between natural key tails and glued down with thick cyanoacrylate glue:


The oily nature of ebony can make it problematic to glue, so the undersides of the sharps were wiped down with lacquer thinner just before gluing to remove any residue that might interfere.

When the glue dried, I put the keyboard and nameboard back into the instrument to see how everything looked:


The nameboard is presently too tall but can easily be trimmed to size later on.

Keyboard: Cosmetic adjustments

I spent a lot of time in August watching the Olympics, but various little things still got accomplished on the keyboard.

Despite drilling the balance pin holes squarely and installing the pins carefully, some the of the keys ended up tilted slightly out of the horizontal, which I think is pretty much normal no matter who is making the keyboard. Correcting this was a threefold process.

First the affected keys had their balance pins tapped sideways with a hammer to bring the key surface level again. However, doing so also moved the key sideways at the same time, creating unequal gaps on either side. That meant the rack pin hole in the affected key end had to be redrilled and the rack pin relocated into the new hole. The new position was about half a hole diameter to one side, which was usually enough to correct the gaps. Sometimes the very back of the key lever ended up rubbing its neighbour after these adjustments, so the rear edge was sanded a little more to restore clearance.

In keeping with historical tradition, I scribed a fine line across the joint between key fronts and backs, and a second line about 4 mm in front of this. The second line will act as a reference point later when the edges of the key fronts are gently rounded over to this mark. These lines are not only cosmetically appealing but also serve as a fine example of our ancestors' tendency to allow construction details to remain visible in the finished product.

Fixing the sharps was a simpler process. First I temporarily laid the ebony sharp caps in playing position and, after a visual inspection, tapped balance pins as above to re-level where necessary. The side-to-side positions of the sharp levers is not that important as the sharp caps are centred at the moment of gluing, but the levers, for cosmetic appeal, shouldn't be any wider than the base of each sharp. I narrowed the sharp levers between the natural key tails by sanding the sides, checking that no wood peeked out when the sharp caps were laid in place. Resetting rack pins was thus unnecessary, and only a little sanding of the key lever ends was required to restore clearances as with the naturals.

Monday, August 11, 2008

Keyboard: Sanding natural covers

It's time to sand the natural key covers. Some of them turned out to be a little irregular, tapering in thickness from side to side. The seam between fronts and backs also needs smoothing out.

I set up this drum sander on the Shopsmith, making it act like a thickness sander thanks to the Shopsmith's adjustable table height. That way not only are the key tops flattened properly but they'll end up parallel to the undersides:


After progressing from 150 grit to 600 grit and giving each key two or three slow passes, the key tops are smooth as glass.

Sunday, August 10, 2008

Keyboard: Sharp reliefs and head stop

A little more tweaking of the keys today:

First I had to cut a little relief area at the back of the natural fronts. When played, the sharps rock downwards in a slight arc, and the naturals must be trimmed back at the junction of the heads and tails to keep the front of the sharp from rubbing. I scribed a knife line at 10 degrees and cut out that area with a sharp chisel:



I also discovered that the keys were rubbing a bit at their back ends. It seems that slicing through the green felt glued to the key ends with the bandsaw created enough fuzz to cause quite a bit of friction between keys, so I sanded the key ends again. That worked: the keys now fall downwards under their own weight, which they hadn't been doing before.

Lastly I stapled a 2-1/4" strip of thick felt under the key fronts as padding to limit the downward travel of the keys. This head stop is a typically Italianate way of controlling the key depth:


Right now the keys are all falling downwards because they are unbalanced, but eventually they'll sit properly.

Saturday, August 9, 2008

Keyboard: Cutting out the sharps

With the keyboard cut apart into sections of 3 and 5 naturals and the sides of the sharps already cut, the next step is to finish cutting out the sharps by cutting through the front part of each with a fretsaw. I used a 32 TPI blade that's about 0.5 mm wide: thin enough to turn sideways and slide down the kerf between sharps and naturals:


Once the sharps were free, the natural sections remained, held together by the key heads:


These were cut apart at the bandsaw, and then the rack pins were inserted into the holes in each key end. Next, the sides of the keys were sanded to eliminate shavings and fuzz (the basswood used for the keys produces long stringy shavings when cut) and to make sure that no excess wood was visible beyond the edges of the boxwood key covers. Then the keys were installed onto the key frame:


Lots of work still remains: the sharps must be glued on, the keys must be balanced so that they fall back predictably, the boxwood surfaces must all be levelled, any unevenness in the key positions must be corrected, the balance pin mortises must be burnished so the keys operate without binding, and so on.

Friday, August 8, 2008

Keyboard: Cutting apart the naturals

The last thing to take care of with the key panel still in one piece is to glue a wide strip of felt along the back where the jacks will sit, to keep them from rattling against bare wood. I used fish glue for this, as it is said to be a good choice for gluing fabric and leather. It won't harden the bottom of the felt too much, which would reduce its effectiveness as a cushion.

Once the glue dried, I put a strip of wide masking tape on top of the felt and retraced the lines between the keys which had been covered up by the felt.

At the bandsaw, I installed a 5/8" thin kerf meat-cutting blade with very little set to the teeth. A wide blade is useful for cutting out keyboards as it tends to cut straight more easily, and a thin kerf means the blade doesn't eat into the key levers too much.

Cutting proceeds in several stages, starting from the back and working towards the front:
  • First, cut the keyboard into octaves along the lines between B and C
  • Next, cut each octave apart along the line between E and F
  • Cut along the lines between sharps and naturals up to the front of the key tails
  • Cut off the lowest (GG/BB) and highest (c''') keys
This leaves a bunch of keyboard sections 3 and 5 naturals wide:


The sharps are still attached at their fronts and will be cut out with a fretsaw.

The two outside keys are already detached at this point, since they don't belong to any of the sections shown above. I installed a rack pin into each and laid them in place on the key frame:

Thursday, August 7, 2008

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.

Wednesday, August 6, 2008

Keyboard: Balance pin holes and rack slots

Keys must be guided in two places to keep them from shifting sideways as they are played. All keyboard frames have a balance rail slightly in front of the midpoint into which balance pins are set. These pass through holes in the keys. The second guide location varies among the various national styles of harpsichords, but a common arrangement for Italian harpsichords is to use a rack at the back of the key frame. A slotted strip of wood standing on edge receives metal pins or wooden slips driven horizontally into the key ends and restricts the keys to up-and-down motion only.

I'm using balance pins of 0.096" diameter and drilling a 3/32" hole to receive them. In order that the holes through the keys line up with the holes in the balance rail, the key panel is simply screwed onto the balance rail, after making sure that the panel is correctly positioned both back-to-front and side-to-side. Drilling holes this way is certain to align them properly, as any slight discrepancy is transferred from one part to the other:


The sharps have their balance pin holes offset to the rear, since their key levers are shorter.

Now for the rack itself. It must fit under the wrestplank so that the keyboard can be installed and removed freely. The key ends pivot in small arcs when played, so the rack can't be right up against back of the keyboard, nor can rack be much thicker than the upper belly rail or the back row of jacks might rub against it. These parameters determine the height and thickness of the board that will become the rack.

I'll be using 1.5 mm pins in the backs of the keys, so I want the rack slots to be 1.6 mm wide. This provides a minimal bit of clearance that avoids having the pins scrape up and down in slots that are too tight. The old makers made their rack slots with a dovetail profile so that the pins wouldn't jam inside the slots, the idea being to guide the pins with as small a contact surface as possible. Another way to accomplish this is to drill a bunch of oversize holes just shy of the front face of the rack:


These 3/16" holes were located by temporarily clamping the rack piece to the key frame and putting tick marks along the face at the midpoints of the key ends. The holes are drilled about 1 mm from the edge.

Next, the actual slots were routed with a 1.6 mm router bit and the table tilted at 8 degrees. No ordinary router table is capable of tilting, but the Shopsmith I'm using can do so, luckily for me. The slots must be angled because the back of the keyboard isn't square to the sides.

Once the slots were routed and residual fuzz cleaned up, the rack was glued to the back of the key frame:


Here it is with the glue dry and 2 screws (not seen) securing the left and right ends to the key frame:


Note that I've already glued the decorative maple arcades onto the key fronts. These are a little wider than necessary so that when the keys are cut apart the arcades will be trimmed flush with the sides of each key.

Lastly I have to transfer the exact locations of each rack slot back onto the rear edges of the keys so that the drill holes for the rack pins will let each pin enter the appropriate slot straight on.

Saturday, July 26, 2008

Keyboard: Natural covers complete

All the natural key covers have now been glued on, and the left side of the keyboard has had a little wood grafted on to correct my miscutting of the key panel:


The last couple of keys in the treble were slotted at the backs of the tails to provide a little room for creating the balance pine mortises. You can see the two lines for these mortises marked in pencil and labelled with a natural and sharp:


Most of the mortises will not interfere with the key backs, so only a few slots were needed.

Tuesday, July 22, 2008

Keyboard: Natural backs

Now it's time to glue down the natural back portions, but this isn't quite as simple a task as gluing down the fronts was.

It all boils down to the fact that the typical keyboard octave is divided into two unequal parts of 3 naturals (C-E) and 4 naturals (F-B) in front, while the back is divided into 5 and 7 parts, respectively, when the accidentals and naturals are considered together (C-C♯-D-E♭-E and F-F♯-G-G♯-A-B♭-B). Thus the rear part of the keyboard has a width of 3/5 of a natural in the lower part of the octave and 4/7 in the upper part: a paradox, it would seem.

What ends up happening depends on how one approaches the process of gluing on the natural key covers. It's possible to glue down one-piece rectangles that are as wide as the key fronts, reaching all the way to the back of the key and overlapping where the accidentals will later go. One then draws out the keyboard design using a keyboard ruler, which is basically a pattern showing where the accidentals are. The backs of the naturals automatically appear in the spaces between the accidentals. The keyboard is then sawn apart, the wood covering the accidentals is removed—a reversible glue like hide glue must obviously be used—and the sharps are glued on.

The second option is to use separate key fronts and backs, and let the act of gluing down the backs automatically leave space for the accidentals. To do so, a few observations on the general layout of keyboards are worth noting:
  • The front and back of C are flush along their left edges (the same is true for F)
  • The front and back of E are flush along their right edges (the same is true for B)
  • The middle of the back of D is aligned with the middle of the front of D
  • The middle of G♯ is aligned with the middle of the gap between G and A

When these facts are digested, the layout of the keyboard using separate fronts and backs is largely reduced to finding the proper position of the backs of G and A such that the F♯, G♯ and B♭ keys aren't hemmed in too much by the adjacent naturals. If the key backs are all identically sized, the paradox described earlier is resolved by letting the gaps between neighbouring keys vary slightly in the two parts of the octave.

To be on the safe side, I took some of my sharp stock, which was purchased in the form of a stick of ebony already milled to the correct cross-section (narrower on top and wider at the base), and cut myself 5 sharps about 2.5" long. Then I temporarily attached natural backs against the fronts in various positions with double-sided tape and checked to see if the sharps fit correctly. The C-E portion of the octave was fine; F-B needed some juggling. With a ruler accurate to 0.5 mm, I made notes of how far each back was from the right-hand edge of the corresponding front for the notes D, G and A.

Here's the setup used to glue the backs:


This is largely the same as that used for the fronts, except the triangle used to align each piece now has the ruler taped to it to help take measurements:


The green piece of tape has the name of each note written on it, as a mistake in laying down the backs would be quite serious. I'm using a thick cyanoacrylate glue to attach the covers, and there's no turning back once the stuff cures.

The far ends of the keys must match the spacing of the jacks, which is of course determined by the registers. This is easily done by laying the register along the line showing the position of the wrestplank gap and ticking off each slot:


These tick marks will be connected to the rear edges of the key backs with pencil lines showing where each key is to be sawed out.

Note that the final few key backs haven't been glued on yet. This is because the key backs come very close to the balance pins in the extreme treble, so I'll have to notch the top couple of backs slightly to allow the key to move without interference.

Sunday, July 20, 2008

Keyboard: Layout and natural fronts

The key frame, key panel and rack have been sitting around since last autumn, and I really need to complete the keyboard, as I need to know how high it sits in the case before I can cut the nameboard to size and apply moldings to it. So I've temporarily allowed myself to get sidetracked.

The key panel needs to stop a bit short of the rear of the key frame to leave room for the rack, a board standing on end with vertical slits in it that will guide metal pins sticking horizontally out of the back of each key. In front, some space for decorative arcades glued to the front edge of each key must be accounted for. The natural key covers overhang these arcades a bit, and the key fronts need to end short of any case moldings along the front bottom edge. After factoring in all these requirements, I cut the back edge of the panel to its final size at an 8-degree angle.

Next, various layout lines were drawn on the panel: a line showing where the front part of the natural key covers falls, a line showing where the nameboard will be, two lines for the balance pins that extend up from the balance rail through the key levers—the naturals have their pins slightly in front of the accidentals, hence the two lines—and a line showing the front edge of the gap behind the wrestplank.

The natural key covers are in two parts, front and back. I purchased these pre-cut and therefore had to spend some time sorting out the various pieces to try and match grain and colour. Here is one half of the total, properly matched:


Covering the key panel starts with the natural fronts. The gluing setup looks like this:


The ruler is exactly along the first layout line, and the yellow plastic triangle controls the side-to-side placement of the key front:


My natural fronts were made a little narrower than the octave span I'm using, so to make up the correct octave size I need to allow a controlled amount of space between each front. I used a feeler gauge to set a gap of 0.965 mm. By placing the feeler against a previously-glued key front, sliding a new front up to it and butting the plastic triangle against that, the correct placement for the next front is assured:


Here's the panel with all but one front glued on:


I left off the leftmost key front for the time being as I may need to extend the left key edge up a bit, having trimmed the panel to width a bit too closely. Oops! (but nothing that can't be fixed, fortunately).

Next up: the natural backs.

Sunday, July 6, 2008

Moldings: Bentside hitchpin

After letting the molding stay in the form for a day, I unclamped it, mitered both ends and glued it in:


I didn't quite bend it enough to fit perfectly, despite trying to bend to a sharper curve this time around, but the additional curvature could be imposed easily enough with minimal resistance from the workpiece, so I'm satisfied.

Before gluing, I had to preserve the hitch pin marks made at the soundboard edge, since they will get covered up by the molding. Using a small square, I transferred them up to the top of the bentside, where they'll be covered by more moldings later on:


Later I will transfer these back onto the walnut molding and drill for the hitch pins.

This completes the walnut moldings, but lots more are to come, made of yellow cedar: on either side of the top edge of all the case sides, all along the outside bottom edge, and a cap molding glued onto the top of the case edges.

Friday, July 4, 2008

Moldings: Steaming the bentside hitchpin molding

I finally got around to working on the bentside molding at soundboard level, which I decided had to be steam-bent. Kerfing with a test piece of walnut looked rather ugly, even though it did allow the piece to bend. The problem is that this molding needs to be bent along its thick dimension, and doing so makes it twist out of flatness against the soundboard. My handscrews don't seem able to clamp the molding while it's trying to twist at the same time.

The steaming apparatus is a consolidation of information from numerous web pages discussing the art of bending wood. I used a 1.5"-diameter PVC pipe 7.5 feet long, capped on both ends with threaded covers. On one end I put a Y-junction into which steam flows from a boiling kettle. In several places I drilled through holes and installed a 2" bolt to act as a shelf on which the wood sits while inside the pipe. At the far end I drilled a small drain hole to allow condensed moisture to exit the pipe.

Here's the setup:


At the far end, the kettle spout nestles into the Y-junction and the connection is wrapped with aluminum foil to prevent the steam from escaping. Bricks keep the whole thing from tipping sideways onto the floor, while at the near end a tray collects condensed water from the drain hole.

After putting my molding into the pipe, it was simply a matter of filling up the kettle, plugging it in and letting it steam for about 20 minutes. The general rule of thumb for steaming is 1 hour per inch of wood thickness, regardless of width. My piece is not even 1/4" thick, but the bare minimum steaming time seems to be about 15 minutes for thin pieces. I gave it a little extra to be sure, then uncapped the near end of the pipe, pulled out the molding and quickly rushed it over to the clamping jig:


This is largely the same as that used to bend the bridge, except that the clamping blocks have notches marginally larger than the width and thickness of the molding. These contain the molding and keep it from twisting out of flatness as it is bent.

I'll let this sit in place for a day or so, then I'll see how it looks when it's unclamped. I screwed my clamping blocks along a tighter curve than when I bent the bridge. The bridge needed a little extra bending at gluing time and I want to minimize that with this piece of molding.

WARNING: in case anyone is thinking of trying to steam-bend wood at home, make sure your steam pipe isn't completely air-tight, or it might burst after it fills up thoroughly with steam. My drain hole provides some pressure relief, and I also have a few unused bolt-holes that I plugged with plumber's putty. In an over-pressurized situation the putty would get forced out and excess steam would safely escape.

Saturday, June 28, 2008

The stand

Once again, several busy weeks got in the way of this project, and when work finally resumed last week, I wanted to do something that wouldn't take too long and would make a visible difference to the instrument, so I decided to make the stand. This also let me take the harpsichord off the saw horses it's been sitting on since last summer, which I've been tripping over from time to time in the crowded basement.


The legs come from Woodturners Incorporated, an outfit in eastern Ontario that sells turnings by Internet and mail order. I picked up 4 maple legs with a 2.25" cross-section, cut them down to 27" in length and joined them together in pairs with mortise-and-tenon joints, using two 3/4"-thick maple stretchers (the upper 3.5" wide, the lower 2.5" wide).

I connected the front and back pairs with two long stretchers, using 2" 1/4-20 bolts which thread into cross dowels embedded into the stretchers. I thought these would be safer than trying to put in threaded inserts, which might have split the thin ends of each stretcher.

The harpsichord is screwed to the stand with three 4"-long bolts that pass completely through the upper stretcher into threaded inserts set into the baseboard. This way I can pick up and move the whole instrument without it coming off the stand. Two dowels in the ends of the legs mate the instrument to the stand and align it with the screw holes for the bolts. It's amazing how many instruments I've encountered that aren't fastened to their stands. This makes repositioning the instrument an annoying task, if not a dangerous one: sometimes moving the instrument even a few inches is liable to tip the whole thing onto the floor!

I plan to peg the mortise-and-tenon joints to give them extra strength. Eventually the stand will be stained a dark walnut colour, which will match the bridge, nut and walnut moldings.

Thursday, May 29, 2008

Moldings: Soundboard level

The next installment in the molding saga: the wrestplank moldings are complete, and the soundboard area is almost done.


Only the bentside molding remains to be glued down. This must be bent to shape somehow; by hand, perhaps, but it seems to tip forward when forced around the curve, and clamping it flat is challenging because it's so skinny. I might try kerfing it slightly along the inside of the curve to take out some of the bending strain.

Shown resting on the soundboard is the neat little miter box I used to cut all the corner miters. I also used it on the bridge and nut. It has a 54 TPI blade that cuts slowly but extremely smoothly: absolutely no sanding is required to clean up the cut.

Wednesday, May 7, 2008

Moldings: Tail hitchpin

It's time for moldings... and there are a lot of them on an Italian harpsichord.

First comes the molding that lies along the soundboard edges, which will hide any little gaps between the soundboard and case. These moldings can also serve as places to drive the hitch pins, if one chooses. Another possibility is to drive them through the soundboard just in front of the molding.

The moldings are based on the same profile used to make the bridge and nut—a cove and a little groove—so the decor has a holistic sort of feel to it, with recurrences of the same basic designs.

I've started with the tail molding, which is both thicker and higher than the remaining moldings. This will lessen the downward pressure of the strings on the bass end of the bridge. When the hitch pins are driven through this molding, they'll penetrate it and the soundboard and go a little way into the tail liner, which will help secure this piece against the tension of the bass strings.

The molding glued in place:


Note, at bottom left, some of the other moldings: same profile but much slimmer. These will cover all the remaining junctions between soundboard and case and will also outline the edges of the wrestplank.

Monday, April 28, 2008

Soundboard glue-in

An auspicious day: the soundboard was finally glued in.

Earlier I checked the fit of the board to see if the presence of the case walls affected the fit. It seemed fine except the cheek edge felt a bit tight, so I gave that edge a little rub with coarse sandpaper and the fit was good to go.

After taping the edges of the soundboard and the inside edges of the case to protect against glue squeeze-out, generous amounts of fish glue were applied to the liners and the soundboard was set in place. An arrangement of clamps and cauls held the board against the liners and the upper belly rail. I admit that in a perverse kind of way I looked forward to this moment, as I was finally able to use 47 of the 50 F-clamps I bought last summer, plus a bunch of C-clamps.








The instrument is respectfully dedicated to my friendly harpsichord maker, and has been so inscribed on the underside of the soundboard.

A day later, the glue was dry and the clamps came off. I used my block plane to trim the front edge of the soundboard, which overhung the upper belly rail a smidgen along its length.

It should be clear in the photos above that I already trimmed all the overhanging case edges, which were left long as each piece was glued in (see the photo in the previous post for comparison). I taped each joint to protect the wood from scratches, and, using a Japanese-toothed dovetail saw held flat against the case, I sawed off the excess material at each joint. A little sanding smoothed out the cut edge, although I didn't aim to get the joints exactly flush at this point in time.