A bridge to an end

Posted in Acorn House on January 3, 2019 by acornhouseworkshop

Before the finish goes on, the last bit of woodworking needs to be done: the bridge. While the steel string world has seen a myriad numbers of bridge designs over the years, the classical world has been far more conservative. While a few builders have experimented with new designs, the majority stick to the traditional model.

It all starts with a blank cut to size. Here, the traditional material is Rosewood. While ebony is usually used for fingerboards, it is to dense and heavy to provide the most efficient transfer of the classical strings’ energy. I’m starting with a wonderfully dark blank of Brazilian Rosewood, marked at the center.

Before doing anything else, the bottom needs to be contoured to match the arch of the top where it will go. If this isn’t done, it will try to compress the top arch to match a flat bottom, and always be an area of tension, as well as compromising the neck angle that was designed in from the beginning. Using scrapers and sandpaper taped to the top results in a perfectly matched arch.

Then the blank goes to the table saw to cut the grooves for the saddle and gully. A handsaw takes care of the edges of the center.

Then the sides are cut to the lower thickness.

Holes are drilled in the tie block for the strings. The tie block then needs some type of harder material to protect the wood from the strings. This can be either two strips of bone on the edges, or a more elaborate treatment. I went elaborate. Using a wide strip of bone, the inside is cut out and more Buckeye burl is inlaid. Then the assembly is glued to the lowered top of the tie block.

Next, the sides get shaped using files and sandpaper; first with a top radius.

Both sides need to match, so calipers and eyes are critical. Then the ends are ramped and the saddle surround is shaped.

Now the bridge is ready for finishing, unlike a steel string bridge which rarely has anything more than oil. The classical bridge gets the same gloss finish as the body, whether it is finished on the body, or off.

Parlez-vous Fran├žais?


Details, details…

Posted in Acorn House on October 13, 2018 by acornhouseworkshop

With the box closed up, some decorative, but functional, details need to be tended to. The major one, that causes the most night sweats, is routing the binding channels. After all the work so far, one little slip of the router, one grab of a weak grain, can ruin everything. Plus, with the Spanish heel construction, you have to work around the attached neck, and do some delicate handwork to bring the channels into the neck. No pics for that procedure, I was too focused on the doing to do any recording. Suffice to say, I, and the guitar, survived.

Bending the binding, on the other hand, proved to be ridiculously easy. The rosewood’s grain was straight, and it seemed eager to conform to the guitar’s curves. I chose some simple black and white alternating purfling lines to accompany it, white-black-white-black on top, and white-black-white on the back. This, with the rosewood binding with just a maple line, gives a very clean, modern look, with no unduly extravagant ornamentation.

One thing I decided to do differently on this guitar, is to inlay the end graft after putting the binding on. Typically, this would go on first, and the the accent lines would connect with the binding’s accent line(s). But I want to use more of the buckeye burl to form a sort of mini framed picture that extends over the binding. So I used some purfling to frame the rectangle of Buckeye.

Then, after routing it’s shape into the end of the sides (snapping a too-small bit in the process, and having to wait for a larger replacement to arrive), the framed “landscape” was glued in, tying in with the soundhole rosette.

Next, the fingerboard was tapered, and the end shaped. Most classical guitars have 19 frets, but some add an extra fret for the high string, allowing a high-C for those pieces that need it. This added outcropping requires a partial fret slot hand cut.

After the fingerboard is glued on, the neck can receive its final carve, the bridge made, and the guitar finished. All after much sanding.

And sanding.

And sanding.

A little dental work

Posted in Acorn House on July 31, 2018 by acornhouseworkshop

With the soundboard finished, it’s time to start a little assembly.

Classical guitars have a different structure to steel string acoustics, and therefore the order, and manner, of assembly is, at least traditionally, a little different. (Some modern builders have taken to doing a more steel string type construction for their classicals; and vice versa.) The soundboard is first attached to the neck, being careful to keep the centerlines aligned. This subassembly is clamped down to the solera and, after the sides are bent, the outer molds are bolted to the solera and the sides let into the Spanish heel.

To attach the sides to the soundboard, little triangular pieces called tentellones, or peones, (or tantalones, or dentelones, etc) are made, along with the end block, from some Spanish cedar.

The tentellones are glued in, one by one, with hot hide glue, needing only finger pressure for a minute or so to clamp them in. This method is a slow, but rather easy way that results in a very secure attaching of the sides; certainly without the time stress and clamping difficulties of using a solid lining kerfing strips. There are two ways to space them; some will leave even gaps between each piece, I used the other way of putting them as close as possible, with minor variations due to the individuality of the cutting of each piece and the curve of the sides.

You can see the side braces that press on the harmonic bars, locking everything together. After a few hours (with breaks as needed, one other advantage of this method) the soundboard is solidly attached to the sides.

The back is attached using kerfing strips, more specifically the reverse kerfing strips I prefer. Since they don’t need to be glued on two surfaces at once, it’s easy, and quick, to clamp them to the sides with reinforced clothespins (a rubber band is wound round the jaws to provide a tighter grip).

Next up, closing the box.

Hidden beauty

Posted in Acorn House on July 1, 2018 by acornhouseworkshop

With the rosette in, work begins on the other side of the soundboard, the side that actually means something. First, the soundboard needs to get it (almost) final thicknessing (the final prep for finishing will take a little more off.) My goal is a nice light 2.5mm, thin enough to become translucent under light, but not thin enough to lose its structure. (Sorry America, the classical guitar world uses the metric system exclusively.) This will vary according to the stiffness of the wood.

Then the bracing pattern can be drafted underneath. The standard classical guitar bracing pattern was established in the middle of the 19th century by Antonio de Torres; with luthiers adding their own variations ever since. Recently there has been some completely different designs, but the classic is still the most widely used. I will be following a combination of Jeffrey Elliott and Robert Bouchet, both of whom derive from Torres’. The first component to go on is the soundhole reinforcement. That big hole is the biggest weak spot in the top, especially with half of its thickness being taken by the rosette, so it is critical that it be supported.

Everything else has to be done in order, since there will be some parts that will be going over other parts. The next critical reinforcement is under where the bridge goes. While there is much less tension with a classical’s nylon strings, vs. a steel string guitar, there is force aplenty to pull the soundboard into distortion. So, on goes the bridge plate.

One element that both Elliott and Bouchet have in common in their designs, is open harmonic bars, basically open ares in the upper horizontal bars. (Something that Torres also experimented with.) However, these openings can then be a point of weakness, so one innovation that Elliott devised, was to place very thin strips at these openings. Being only 0.5mm thick, they do not inhibit any vibrations, but they add enough reinforcement to counteract that weakness. They are almost as thin as the fine pencil lines.

So, these are next to go on.

With those on, the fan braces can be added. I drew them to radiate from the point at the 12 fret where the neck joins the body. They will cross over the first bits wherever they intersect. They are 6mm wide, and will range from 6.5mm to 5mm high. While classical and acoustic guitars appear to be flat on top, there is actually a slight rise at the bridge. This dish is built into the workboard as a concavity, and each fan brace must be be fitted to match it. Compare the shape of the fitted brace, with the straight drawn line next to it and you can see this radius.

With each brace crossing the dish from a different angle, the individual fitting is the most time consuming. After conforming to the dish, they are then notched to over the bridge plate and thin reinforcement strips. Eventually, all 7 are glued on. (I’m using hot hide glue for all of the bracing, by the way.)

Out come the wee little planes and paring chisel to shape the fan braces, starting with the planned heights, then profiling them, finally ramping them down on each end.

The two upper fans are next; fitted, glued, and carved.

Now the open harmonic bars can go on. The open areas allow vibrations to go into the upper part of the guitar while providing the strength under the fingerboard. They are notched to go over the tips of the thin reinforcement strips.

A couple of other reinforcements, and the bracing is done. A light, but strong, under structure that will, sadly, never be seen by most.

Siding next.

A burly circle

Posted in Acorn House on June 28, 2018 by acornhouseworkshop

With the neck shaped as far as it will go before assembly, it’s time to give the soundboard it’s face. I’m using a very resonant soundboard made from Italian spruce harvested from the Val di Fiemme; the same forest that Stradivari used for his wood (although his wood was decidedly more old growth.) This wood rings with potential, and is very stiff.

For the rosette, I decided to use some buckeye burl I had left over from a bowl I turned. The slices I was able to get revealed a beautiful, complex combination of shapes, swirls, and shades (I’ve wiped one slice with mineral spirits to show its finished appearance.)

After gluing 2 pieces of craft paper (for ease of removal), I laid out the rosettes inner and outer diameters, and started laying out the slices.

With all 3 pieces on, I redrew the circles. The unfilled area will be hidden under the fingerboard, no need to waste good burl.

If you can see the way I butted the pieces up to each other, my original plan was to have an arc of black to hide/emphasize the seams. A good night’s sleep revealed a better idea. Using some ebony, I drilled some holes to end up with small, double arc’d, bits.

These were then inlayed between the burls and the border circles were routed.

Next, I had to decide how to frame the burl. I experimented with various combinations of purfling, using black, white, and even green lines.

While I like the way the green brightened things up, in the end, I went with a variation of black and white. If I had used either of the green variations, the rosette would end up being far too wide, and the soundhole would have to get for too small. Alternately, I could have had the purfling go into the burl area, but, the burl was kind of the whole point; I wanted to keep as much of it that I could. I did vary the thicknesses of black to add some dynamic to it.

So, the burl was inlayed into the soundboard, with some Sitka spruce scrap filling in the area underneath the fingerboard.

Then, channels were routed for the purfling and it was glued in. After leveling the burl and purfling, a couple of voids in the burl were filled, and the soundhole was finally cut. The top was shellacked to bring out the burl, as well as protect the top during the rest of the construction.

Its a more modern take on the traditional classical rosette, which is made up of repeating mosaic tiles, with many surrounding purfling elements, but one that I prefer.

Brace yourselves, next up is the bracing!

Getting a head start

Posted in Acorn House on June 6, 2018 by acornhouseworkshop

This summer’s main project is a classical build. Since the traditional neck to body joinery is a Spanish heel, with the sides let into slots cut in the heel, the construction timeline dictates that the main parts of the neck need to be done first. So, after gluing up the rough blank from Spanish cedar, the design of the headstock starts. I tried to draw upon various models from the classical tradition, as well as incorporating elements from my own previous headstock designs. So, I came up with this:

Since there is typically no inlay in a classical headstock, it is the shape itself that is the hallmark of the builder. Being satisfied with this design, I glued on the overlays (and underlay), and began to rough cut the outline. An errant saw cut got too close to the little tip at the top, which meant a redesign was required. At first I was going to go with a three lobe design, using the original idea, just without the tip. But, after refining it closer, I could see that that wasn’t going to work.

So, I added some curves to the outer lobes; again, drawing inspiration from historic builders.

That resulted in a design that I liked even better than my original concept.

Next, the tuner post holes were drilled, and the access slots were drilled, cut, shaped and ramped. Some finish sanding and a little shellac to seal everything and show the true color of the Rosewood, and the head is finished.

Now, to move from head to toe.

Feature Presentation

Posted in Acorn House on November 14, 2016 by acornhouseworkshop

A little interview/performance I did about my work.

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