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Saturday, May 14, 2016

The Luthier: Part XII- Perfling and Bridge

Last time, I had just permanently attached the neck to the body, and at last the mandola was beginning to look like a thing with intent behind its construction. A slight oversight when cutting the depth of the external bit of the neck heel left it shorter than I would have liked. Although structurally and visually (later on) this will be a non issue, I needed to fix it anyway for my own peace of mind.

Fortunately, I hoarded all the scraps and cuttoffs throughout the project, so finding a bit of extra rosewood was easy. This post marks the beginning of my time, once again, without a shop to work in. As a result, progress happened much slower than before. Fortunately I was so near the end when I moved that most of the difficult or impossible-to-perform-without-a-shop tasks are behind me.

To fit the shim, I had to whittle it down. Ordinarily I would have used a plane for the task, but I have no bench to work on or clamp things to, so I quickly abandoned that effort and turned to a chisel. Because this will be hidden by the perfling anyway, perfect fit is not of the utmost importance.

Good enough. As it is not structural, there really only needs to be something to fill the space.

After gluing the shim in place, I carefully cut it as close to the shape of the neck's heel as possible. The less work with chisels and files to clean up the profile the better.

Three or four cuts with the saw and the rest was to the chisel to clean and round. At this point I had to pay special attention to the grain direction, as my previous experience with the rosewood left me weary. Nowhere near as bad as the cedar, the grain still likes to splinter and lift in inopportune places.

Perfling is, before I went into this, one of those things that I assumed would be easier than it actually turned out to be. For a long while I debated with whether or not to cut a groove in which to inlet it, but the longer I dwelt on it the less desirable that thought became. So, in the end, I devised a less sophisticated way of accomplishing something similar enough.

With the wood I ordered for the project, I had a few extra bits that I could not identify or find other uses for, so they turned into perfling. I suppose here is where I should actually say what that is. Perfling is, simply put, those bands of decorative trim that cover the seams of the top and back with the sides. They do add a bit of contrast and decoration as well, but that was not my primary intent behind them. If you will recall a few posts back where a weight slipped and fell on the sides, crushing a good portion of the fibres, the perfling will conveniently hide the imperfections of that repair.

Returning to those erroneous bits of wood, I used them to make my own perfling. I do have some ebony bands as well, but they were not long enough for the coverage I wanted. Paired with these ones I made, I was able to make a two tone band along the sides.

Using my wheel marking gauge and a scrap of the soft cedar, I was able to use it like a lacing tool to cut a bundle of thin strips of fairly even consistency. All in all, I cut until I was able to match the length of the ebony ones. 

I have seen a few luthiers use an elaborate string and wedge setup to affix the tops and backs and perflings to their instruments, but I didn't want anything to do with that so I used tape instead. One small bit at a time I used a small piece of the fresh cut perfling scrap to apply glue to the ebony. Once placed in the right position, I taped it and moved on to the next small bit. It was slow going and the corners were difficult to navigate, but it eventually worked out.

Top and bottom, the body had its first band of perfling. At the inner and outer corners, I started by cutting the strip and trying to match it on the other side. Its results were less than impressive, that slight shift that crept in during taping throwing off the line, so I began carefully bending the perfling instead. There were some visible broken fibres, but it was better than the alternative. In an actual shop with a proper place to work (and more importantly make a mess without worrying about it) it might have ended differently.

It is a bit hard to see in the above photo, but the second band is being glued there. Just below the ebony, the mystery perfling provides contrast for the black that otherwise blended too well with the rosewood.

With each small bit of length I pressed it tightly up into the ebony and taped, occasionally undoing the work to slide it up and close any devious gaps that opened when I had my back turned.

And here you can see the finished result. I am sure that there are easier ways to do this, namely getting perfling that is pre-cut. Now, to blend the difference in height of the two perflings and the body itself. The ebony is the thickest, then the stuff I cut, which sat about 0,5mmm above the sides. A bit of careful sanding blended the steps into a wedge shape. Not flush with the sides, it does protrude a bit and is only noticeable when looked at from an askance angle, but that is the least of my concerns at this point.

Shifting processes radically for the second half of this post, I'll be working on the bridge now. From here on out, a lot of things happened simultaneously, so I had to restructure some things out of chronology to make sense of it.

Although I ended making two separate bridges, this one sounds the best and is the more interesting of the pair. Late last year, a good friend of mine gave me some old ebony piano keys. In their former life, they probably made both beautiful and mediocre music alike. As ebony is decently hard, it made for an excellent material for the bridge, and combined with its past, this repurposed future drew me to it over all the other materials I have at my disposal.

A little worse for wear, the key needed some work before taking its new form. A combination of planes and sanding brought its sides back to flat and worked out some of the splintering from where they had been removed from the rest of the former piano's key assembly.

As I said earlier, a lot of things were happening concurrently here, and I already had the final width of the strings determined. With that information, I could then mark on the nut (white thing there on top of the ebony) against which the strings press. For the second bridge, I used the ebony alone. With this one, I carved a channel to hold the nut block.

Some maths later, I returned to the marking gauge and scribed lines for the channel. Ebony is, as I learned once again, very prone to splintering if some care is not taken. 

Having no chisels narrow enough to carve out the channel effectively, the terminations of the groove were a bit rough at first. Several laborious minutes or hours later and the visible edges were looking better.

Since I did not have any appropriate chisels, I remembered I have a router plane. As it would turn out, one of the blades for it is the exact same width as the nut block. What luck!

With that groove already started, the plane can do its thing. In the ebony forming and shaping process, I made it a tapered trapezoid, which is not ideal for the plane's fence, but the channel depth was already sufficient for me to guide it with my hands. 

Several test fittings determined that the groove was square and, above all, an extremely tight fit. This is important because I do not want to use any glue in it and the slightest of gaps or vibrations will ultimately distort the sound. Having never played guitars or other stringed instruments, I did not realize that the strings resonating through the bridge into the body is what really gives sound to the strings when they are strummed or struck. There is an incredible difference between what it sounds like with and without a bridge. At first, I was worried that I did something severely wrong when I plucked a few strings and it sounded like it was dying a quiet, quiet death. 

Anyway, with the nut seated I was able to determine the bridge's final height based on how far the strings are from the body end of the fretboard. Ideally, they should be closer than I initially expected. 

With that carving, planing, and sanding done, the bridge is ready to be seated with the strings. Next time, I'll be applying the finish, putting the tuning pegs in the headboard, the tailstock on the heel of the body, and stringing. Depending on if I am able to finish a few other final details that remain, it may at last be the conclusion of this project.

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