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Upcoming projects:
Building a Frame Saw
Forging a Copper Kettle
Making a pair of leather work boots
Forging and Fletching a Bodkin
Flocking a drawer interior

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.

Saturday, May 7, 2016

Introduction to Screen Printing

For some time I've been trying to figure out how to effectively carve stamps for ink printing on fabric without much success. A few weeks ago I remembered silk screen printing and, at a glance, it seemed to be the perfect solution. Because I am not well versed in the process and I would rather not become largely invested in the equipment, I did some figuring and came up with a simpler or smaller solution to parts of the process.

First off, I needed to make the patterns. These need to be printed on transparency film and act in a way like exposing photographs, except the paper will be a photo sensitive resist on the screen. Everywhere I have read, exposing the screens requires a bit of trial and error, so I came up with some designs of varying detail and size to work with.

Here is the first change. Usually the frames for screen printing are rectangular for obvious reasons (the silk and transparencies are both rectangles) but I found that the silks themselves without frames are significantly cheaper. So, instead of getting a frame, I used an ordinary embroidery hoop. Getting the tension was a little tricky but once it was set, I had no problems with it. One thing that can be seen are a few hard creases in the screen, which is an unfortunate result of the shipping. Ultimately, this had no effect in the print.

Next up, the screen needs the photo emulsion resist. This is, once mixed, a sort of light sensitive paint that makes the screen usable. Once exposed to high intensity light for a short period of time (or a lower intensity light for a long period of time), the mixture hardens and its washable characteristics are removed. Areas covered by the pattern are not exposed, and thus able to be washed away, leaving clean screen through which the ink can be passed.

In spite of the very obvious and boldly stated instructions that tell you to add water to the diazo (activator), a great many people complain that the diazo is dried out and does not work. Imagine my surprise when it worked perfectly when I followed the provided instructions.

From a weird blue to an even weirder green, the photo emulsion also changes consistency slightly when the two parts are mixed. Make sure that it is thoroughly mixed, or parts of the screen may not cure properly.

One thing that I could not find anywhere online before physically having the emulsion is the shelf life once mixed. After adding the diazo, it can be stored in a refrigerator for up to four months for later use.

Now then, to prepare the screen, I poured a line of the emulsion over one edge and used a squeegee to spread it thinly and evenly across the screen. Be aware that any uncovered place will allow the ink to pass through it, so covering as much of the screen as possible is recommended. Once I had the one side covered, I flipped it over and smoothed over the back with the squeegee. Removing excess is important, or the emulsion will pool in droplets while drying, which is undesirable for its inconsistency in curing when exposed.

Once the emulsion is spread over the frame, let it dry in a dark, not overly warm place. I shut it in a closet for a few hours, checking on it periodically to ensure there was not any pooling and, if needed, using the squeegee to gently spread out the emulsion again to correct it.

This was the first effort, which eventually did not survive due to under exposure, but the process here is the same. Careful to not tape over the middle (which would cause the emulsion beneath to be unexposed), I taped the negatives on the screen. If you have clear tape, problem solved. When placing the patterns, be cognisant of which side you place them on and in which orientation. The side of the screen that is flush with the frame will be down when printing, so in the orientation I have the stencils currently, the final printing will be mirrored. You can expose from either side depending on how you set up the light configuration, but this is the only side I could use, so I had to have my stencils flipped over because this is the 'underside' of the screen.

In order to keep the stencils flat on the screen, and since I do not have a lightbox, I had to improvise a little. I do not have any clear glassware in my kitchen and, I realized, virtually nothing made of flat glass at all. So, I clamped the screen to the door of my shower, which is why I had to have the negatives on the above side of the screen. Having a piece of flat glass or plastic would do just fine to keep the transparencies flat to the screen, really whatever works. Or, you could probably get away with just taping all the edges down with clear tape as long as the light you are using to expose it with is not overly hot.

Exposing the screen is where the trial and error comes in. I exposed three before getting it good enough to print, and it is still not perfect. As per the instructions of the photo emulsion, using a 250 Watt lightbulb requires 7~8 minutes depending on the size of the screen. This did not work for me, so I tried again at 9 minutes, and it was closer, but still not great. The third time I went for 11.5 minutes, and it was functional but a bit over exposed. The problem with this is the emulsion under the negative becomes harder to wash out and damages the exposed bits in the process.

After exposing, wash the screen. Almost immediately, the unexposed parts begin to appear as the emulsion washes out. Gently using a soft toothbrush, the pressure of the water, or your fingertips to clean the screen, wash until until all the areas to be printed are white again like the original screen.

Now, it's ready for printing. The squeegee presses against the screen, so the side of the screen flush with the frame needs to be down.

With a rectangular frame, it is a bit easier to print because you can use a squeegee that is the same width as the screen, but for a round frame it's not as smooth. Laying a line of the ink down on one side, press firmly on the squeegee and spread the ink over the entire area to be printed, bringing the excess off of the printed pattern. Then, just lift off the screen and there you go!

Once the print is made, it needs to be cured via heat. For cloth, the easiest way is to use a dryer on high heat. Note the ink needs to dry to the touch first or it will get everywhere. After curing, the ink is washable in ordinary settings. This was the first printing and turned out a little rough, but I learned a lot from the process and what to expect.