Week Two: March 5-11

I managed to get down to the shop during the week and do one quick chore, which was to cut and glue the heelblock to the neck blank. The rest of the operations on this page took place on the weekend.

The heelblock was cut in a single block from the big log seen in last week's pictures. The total height of the neck and heel at the juncture with the guitar body is to be 3-1/8", so there was plenty of wood in the 3x4x30 after the 3/4x3x24 was cut out of it. Here it is being glued to the neck blank. The position is determined by the planned position of the 14th fret - the neck-to-body juncture. The heelblock ends 3/4" past that point to provide wood for the tenon that will hold the neck to the headblock.

A little terminology here. From one end to the other: The Headstock is the piece of wood at the far end of the guitar that will be cut down to become the peghead - this is familiar as the place the tuning machines are mounted. Peghead veneers are laminated to the front of this piece to provide strength and to hide the scarf joint made last week. The other side of the scarf joint ends up where the carved curve of the neck meets the flat of the peghead, so it's disguised by the complex geometry of the area. The next part is the neck shaft itself. The fingerboard with the frets is glued to the front of this, with the nut at its very end. The nut has the notches that the strings run through, and determines the spacing of the strings at the "head end" of the neck.

At the other end of the neck is the heel -- right now, until it's carved, it's called the heel block. The heel is the deep part at the end of the neck that joins to the body of the guitar. It ends in a tenon (sometimes a dovetail tenon, but not in this guitar), which is a projecting piece of wood that mates into a recess in another piece, which recess is called a mortise. The piece on the guitar that contains this mortise is called the headblock. The headblock is just inside the body of the guitar at the "top" end.

I think that covers the terms we're going to be using for the moment. The next job is to install the truss rod. The adjustable truss rod is now a standard feature of steel-string guitars, both electric and acoustic. Classical (nylon-stringed) guitars don't use them, because the string tension is so much less that the neck is likely to stay straight without help. A little digression here. When a guitar fretboard is absolutely straight, it won't play properly, because the strings vibrate both side-to-side and up-and-down (and every way in between) even though the plucking action may be side-to-side. On a straight fretboard, the up-and-down vibrations would hit against the frets further down the neck causing buzzing or even wrong notes. So a little relief in the fretboard is called for. This relief is a slight curvature along the fretboard away from the strings. So that if you were to fret the string at the first and fourteenth frets, you would still see a little daylight between the string and the fifth fret.

This relief is automatically provided by the tension of the strings pulling against the neck; but it might be too much, or after some time, the neck may tire and bend a little too far, raising the action - the height of the strings above the frets - so high as to make the guitar unplayable. The truss rod is able to correct this by introducing a reverse curvature inside the neck. The simple adjustable truss rod consists of two steel rods firmly attached at one end (or, usually, one rod bent double) and with one (upper) rod held stopped at the other while the other (lower) rod can be shortened, by turning a nut threaded on to it. Pulling in on the lower rod forces the upper rod into a downward curve. When this pair of rods is embedded in the neck, its curve forces the neck to bend back a little, restoring the relief to the proper amount.

The truss rod is not able to adjust a bad high action on a guitar - although the results of a truss rod adjustment can seem to do this. All the truss rod can to is to force the neck to bend backwards, which helps only if the neck is bent too far forwards. (Some truss rods are two-way adjustable, that is, they can add relief as well as reduce it, but the one going into this guitar is not that kind).

The neck shaft is given a 1/4" groove, 9/16" deep, to accept this Luthier's Mercantile "TRS" style truss rod. The rod itself is seen in the foreground of this picture. It's wrapped in heat-shrink plastic to keep it from rattling in its groove. The rod is not glued into the neck, but just laid into its groove. I didn't take a picture of the process of making this groove, because I had both hands on the router! Perhaps I'll go back and make a pic of the router set-up, which involves a standard router "fence" that attaches to the bottom of the router and slides along the side of the neck, holding the router bit at a fixed distance from the edge of the neck. Item to remember for next time: the router fence comes in a "U" shape with two pieces that ride the edge. The face of each piece has a hole for mounting a continuous piece of material to serve as a solid fence -- make that solid fence! This operation will be much less nerve-wracking at the lower end of the neck!

Here the rod is in the groove, with its rectangular block hanging out the end of what will be the neck tenon. The block has a blind hole for the upper rod and a through hole for the lower. The lower rod is longer and it's threaded on the end, accepting a long threaded sleeve that can be adjusted with a hex key through the soundhole of the finished guitar.
This photo shows the end block of the truss rod as well as the markings on the neck for cutting the tenon. The line across the neck marks the distance of the fourteenth fret from the nut: this will be the place where the neck joins the body. The lines running from this line to the left mark the edges of the fingerboard: the neck blank will be carved back to these lines. The lines running from the juncture line to the right mark the edges of the tenon. The wood outside these lines will be cut away to leave a protrusion that will fit into the body of the guitar, into a matching mortise in the headblock. Those paying attention will notice that the part of the neck shaft that overhung the heelblock has been cut off.

The truss rod will be covered in its groove with a spline made of rosewood. Any strong hard wood will do for this, like maple or white oak. This spline prevents the truss rod from bearing right against the underside of the ebony fingerboard, which it might crack. Sealing the truss rod into the neck this way would also help, I think, to make the action of the truss rod produce a smooth curve in the neck, rather than a kink.

Planing the rosewood spline down to fit into the groove leaves a lot of red streaks on the sole of the plane, and on the workbench, too. Rosewood is beautiful and strong, but it's a problem to work with. It dulls the edges of tools that are used on it, because of mineral inclusions in the wood, which also help to provide the color we prize in it. This red streaking will have to be cleaned off the plane sole before it can be used on any lighter-colored wood that's going to show on the guitar.

That color comes with oils and resins that can interfere with glue doing its job. In order to help the glue, the rosewood spline is washed with acetone. As you can see, a lot of color comes out on the paper towel used for this, without appearing to reduce the color in the wood piece at all. The acetone treatment seems to work beautifully on the sole of the plane, as well, and to a lesser extent, on the streaks on the workbench top. The acetone, as you can see, came from the drugstore in the form of nail polish remover. Be careful not to get nail polish removers with "proteins" or "nutrients" in them...which is just about any ordinary nail polish remover on the market. This brand is marketed as "professional" n. p. r. consisting of "100% pure acetone". It's a little cheaper than the "Cutex" and "Revlon" brands with all the additives.

The sides of the spline are coated lightly with yellow glue, but the bottom is avoided - we don't want to glue the truss rod in, as it needs to be free to move within the neck. The clamps from either side really do provide some pressure against the spline, though it looks like they would not. But the geometry is such that it makes sense: the neck is 3/4" thick, and the groove is 9/16" deep, leaving a bare 3/16" underneath the truss rod - before carving! No wonder it can bend the neck back so easily!

After the clamps come off (it's Sunday afternoon now), the spline is planed down until it's just a small nub along its length.

To finish leveling the spline in its groove, a scraper is used, in order to have better control in not gouging a hollow into the neck face. The scraper is simply a flat, rectangular piece of high-quality steel. To prepare it, the edge is rubbed flat on a whetstone on both sides, then perpendicularly to the stone. This ensures a flat edge that's square to the sides. Then a "hook" is burnished onto both sides of the edge by running a smooth, very hard piece of steel along the edge with a slight angle -- either a purpose-made burnisher or the side of a chisel. This draws out the metal on the edge of the scraper into a sharp hook that can take very fine shavings, as you can see in the photo. You flex the whole scraper slightly, then pull the edge along the wood, tilting it toward you so as to make the hook "bite" into the face of the wood. It's very easy to control just where you're scraping and leaves behind a very smooth, shiny surface. The scraper will be used all over the guitar for finish-leveling surfaces and very controlled, delicate cutting.

The excess wood -- the "cheeks" -- of the neck tenon are cut away along the lines shown in a previous photo. This is done with a hand saw, in this case the trusty old dozuki, or it can be done with a table saw. You might be able to see in the photo that the faces that will meet the guitar body are angled slightly back, to make a close fit to the body easier. The gap will be covered by the fingerboard on top and the heel cap underneath, so nobody's the wiser. This step should be done before the installation of the truss rod, but I got carried away and went out of sequence. No harm, assuming I'm going to do the tenon by hand. It makes the table saw method impossible!.

The next step is to attach the peghead veneers. These hide the scarf joint and add strength to the thin peghead, which is under a lot of tension from the pull of the steel strings. Usually a steel-string will have a single dark veneer for this purpose, and a classical may have two or three of contrasting colors. My materials came with a thin maple and a thick rosewood veneer, and waste not, want not is my motto, sometimes. I'm going to install them both. Cumpiano and Natelson recommend a complicated method for installing more than one veneer, involving registration pins and so forth to keep them from sliding around, but recommend just clamping down a single veneer. The pins and so forth sound like more trouble than doing the whole job twice, so I'll glue down the maple veneer, clamp it for half an hour, then pretend it's a solid peghead and glue and clamp the rosewood over it.

Before doing that, I take a well-squared block of wood and glue 100-grit sandpaper to it (I'll use this block a bunch, I'm sure), and dress the face of the peghead, making sure that the line of the angle comes right up to and lines up with the line marked for the back edge of the nut. I then stand the sanding block up on edge on the face of the neck. Holding the veneers together flat on the peghead, I rub their ends side-to-side against the sandpaper. This gives them the proper angle to sit up square against the nut when it's installed later.

Being careful to cover the peghead face entirely, I smear a thin layer of glue evenly over it and lay the maple veneer down. With a thin caul beneath the peghead to protect it, and a thick one on top to distribute the clamping pressure, I give it six clamps loosely, then slowly tighten them. I have to loosen them and retighten twice to correct slippage of the veneer; I'm trying to get it exactly up to the line that denotes the back face of the nut. After half an hour (occupied otherwise, as you will see) I take off the clamps and cauls and repeat with the thick rosewood veneer. Note that the handles of the clamps are alternated up and down to keep them from interfering with each other during tightening. Except for the big red ones, which go wherever they want to.

Here's the headstock with the veneers glued on.

And what was I doing while the glue was drying on the veneers? I'll digress a little. When I was in the planning stages of this project, I sent away for several sets of measured drawings of famous guitars. I knew I wanted something in the finger-picking style, a smaller, crisper guitar than a dreadnaught strummer. Among others, I located two sets of plans for an "000" - sized guitar and ordered them from Luthier's Mercantile and from Elderly Instruments. These turned out to be identical sets of drawings of a Martin Grand Auditorium with fourteen frets clear of the body. Elderly, by the way, charges $3.00 less for their plans than LMI. I decided to build from these plans. What I did then was to designate one set as sacrificial, to be cut up to make templates. I cut out a half-guitar from the sacrificial set and spray-glued it to a piece of 1/8" plywood to make a body template. I bandsawed around the paper and smoothed out the curves with a microplane rasp.

I used this template to trace out a full-sized guitar body on two pieces of 3/4" ply to make a workboard. The workboard is cut 1/2" larger all around than the guitar body, and has a short neck extension for clamping it to a workbench and a shorter tail extension for some fixtures that will come later. This kind of looks like the back of a jumbo archtop, doesn't it?

Lacking clamps that can reach out to the middle, I weight down the two pieces for gluing with whatever is handy.

And so to bed for this weekend, the second of the great homemade guitar documentary. I had hoped to get a little further this weekend, but slept in both Saturday and Sunday. The following weekend was worse in terms of the project. Work and social commitments prevented me from getting into the shop at all. I picked up the following weekend, though, on the rest of the operations on the neck.

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