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Saturday, April 2, 2016

The Luthier: Part X- Headboard, Fretboard, and Rosette

With the damage of the previous mishap fixed, it is time to begin the final stages of assembly. Before attaching the front, there are a few items that need attention. Namely, laying the fretboard and cutting the sound hole. At this time, I also drilled and cut the holes to accept the tuning pegs in the headboard.

To hold the tuning peg assemblies, I needed to drill a series of three holes and route a slot on the perpendicular face. After some deliberation, I chose a bit that was fairly close, but the cylinders of the tuning assembly are a strange size that perfectly matches any of my bits, whether for the brace, forstner, spade, or conventional bit sets.

Careful measuring of the spacing and alignment made me realize that there is virtually no margin for error in this operation. At the time when I ordered the hardware for this project, I tried to find pegs that were a top-down alignment instead of a side insertion like I have, but the options were limited and significantly more expensive. That look, in my opinion, is better suited to the style of the body, but I had to work with what I had available.

In a scrap 2x4, I made a series of test holes to gauge my layout and accuracy with the brace. With the angle gauge set perfectly vertical to the plane of the board, I followed it on two axes for whether I was drilling square.

Fortunately, the pegs fit tightly and flat against the edge. Because the holes are a hair larger than the cylinders, they do not need to be absolutely perfectly parallel to the wide face of the board.

Onto the real thing. This was largely stressful because the need to follow the line of the headboard is absolute. Less than a degree and a half tilted forward or backward and the hole would rip through the offending side.

In the end, the first side was a success. Shortly after, the second was finished to the same end. All along the headboard, I marked the relevant dimensions of the pegs. Namely, the start and end of the edge, the limits of the cylinders, and where the hole for the string is located against which I can centre the routed slot to be cut.

Due to the depth of the pegs, it was not possible to angle the headboard much beyond its rectangular form, another reason I regret being unable to find pegs of the other orientation.

A little shaping later, and the headboard is about as developed as it can be. During the drilling, I realized that the two sets were mirrored, and can only fit in the headboard in one orientation (based on which end is longer due to the worm gear placement). This was an important distinction to make, as it dictates how far down I could safely cut the top scallops. More than anything, being consistent is all that matters.

Next, I measured an approximate width for the slot and took an appropriate bit. Centred on the centreline for each peg, I drilled down entirely through the headboard.

As a good practise and to prevent splintering the very splintery sapele, when the threads of the bit poked through, I stopped, turned the neck over, and finished the hole from the other side. This way, the wings of the cutting face scribe the fibres and leave a clean hole on the back side.

With all six holes drilled, it is time to remove the web between them.

Via a coping saw, I cut away the web and created a rough rectangular/ovular hole that ran the length of the pegs on either side.

Rather than risk cutting in a place I should not have cut, I left a bit of material in the thickness and use a chisel to flatten the surface. Had I been paying closer attention, I would have realized that I came dangerously close on one side to cutting the outside edge too thin, and as a result it sits slightly asymmetric.

For now, the headboard is finished, and the peg assemblies will be returned to their box until final assembly much later on.

The next order of business is to attach the fretboard to the neck. This will ultimately enclose the truss rod and set the stage for being able to close the body with the top, although those two are for the time being, independent.

Removing the waste on the top end was simple enough. Here, it is important that the cut face is perfectly perpendicular to the face of the fretboard, as the upper nut will sit directly against it.

The initial placement shows that there is a gap between the nut and the headboard. Looking back, this is an obvious result of how the rosewood was attached to the headboard.

With the use of a rabbeting plane, the corner is made square and the gap closed.

In preparation for gluing on the fretboard, I placed a layer of packing tape over the top of the truss rod. This temporarily prevents glue from leaking into the channel and forming a layer between the metal and the wood.

A healthy layer of glue applied to the neck, and the tape comes off.

And then the fretboard is glued in place. The upper nut, although not currently glued in place, is used as a spacing guide for the fretboard placement. Using as many clamps as I could fit, and support on the underside of the neck to prevent it from bending, shows a thin line of squeeze out of glue all along the perimeter. Unlike most of the others, this joint is not merely aesthetic. A poorly mated surface here could mean failure of the neck under tension of the strings and the truss rod.

While the neck dries, I turned my attention to the last piece of this post, the sound hole and the rosette. When I began laying out the braces, I marked the centre of the sound hole. Because the cedar is so prone to splintering, I need to transcribe it to the front, from which side I will do the cutting.

After a bit of measuring, I have that same intersection marked on the front side. Since I will be inlaying the rosette, and I do not want to have the cut positioned such that it hits the top brace, I need to be certain that it is actually marked in the right place.

From the back, I drilled through the centre of the sound hole.

 Which aligned very closely with what I marked on the front. Only about ,5mm difference to the right and top, which is close enough for me.

On the back, I marked on the rosette where the four 'corners' intersected the drawn lines. From that, I was able to use the same positioning (mirrored to the other side of the rosette in case it was not perfectly round) to mark where the rosette should be placed on the top.

With two small drops of glue, I temporarily attach the rosette after the same fashion as when laying out the braces for the top and back internal skeleton.

Then, when the rosette would not move, I scribed the outside with a marking knife. It was incredibly important to do this cleanly,  as it sets up how clean the inlay will be. Deviating from the edge of the rosette means that mark will remain after the waste is cut away.

None of my saws have a deep enough throat to make this cut, so it needs to be done the long way. All around the interior perimeter I drilled closely spaced holes, then carved away the webbing.

Several hours later, I have a sound hole. In the beginning I was largely sceptical that I would be able to make a hole perfectly circular enough for the rosette to fit without a gap, and fully expected to leave it as shown above.

After a bit more patient fitting and adjustment, the rosette fit!

In a few places, there were small gaps. Small enough that they were not really a problem, but large enough that I could not ignore them. To rectify this, I took the ebony offcut from the fretboard and sanded it down, collecting the dust.

Mixed with the glue, it became the same colour as the rosette, allowing me to use it in a very minor space filling capacity.

The only problem with this was that cleanup was a problem, as it dries black. In the end, it worked out as well as can be expected.

Finally, the last brace needs to be cut. With the lower edge of the sound hole as a reference, I was able to cut the bit to length, ends angled to fit the cross brace. Using the same curve template as before, I marked and cut the ends, and glued this final internal piece in place.

That's it, for now. Next time will be joining the top with the body and installing the neck.

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