Monday, January 30, 2012

Graduation Day

In my last post, we took at look at the arching work I've performed on the top and back plates of my "A" style mandolin. An arch is basically an inverted U shape. That shape has an inside and an outside contour. Arches serve the function of supporting much greater stress loads than a horizontal plane is capable of. They are seen in architecture four thousand years old and in centuries-old stringed instruments. The arches give a great deal of strength to the box and make the usual multiple braces found in flat topped instruments unnecessary. This allows for less impediment of vibration thus yielding greater volume and more pleasing tonal qualities. The inside arches of musical instruments are referred to by makers as graduations. This is a more specific term because the wood is removed methodically to achieve smooth transitions from thick to thin. The thickest part of an instruments' arch is generally the center of the plate, perhaps in an oval shape and just under 6mm thick. The outside areas of the workpiece are typically the thinnest areas and they measure out to about 3mm. What precision tool do we use to accomplish this showstopping feat? Why, it's the good old drill press.

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Two simple features are key to this somewhat unsettling technique being a friend you can trust. First is the reliable depth stop. Out of 4 or 5 drill presses at the school, less than half of them have a functional depth stop. That is like having a car with brakes that only work sometimes. So we use one press and one press only for this job. The other lifesaver is the device located directly under the drill bit and chuck assembly. It is basically two threaded pipes fitted together. For every one full rotation, the overall length of the two pieces is increased or decreased by 1mm depending on the direction that you turn them. This rotation has been accurately subdivided into 10 equal parts and thus we have tenths of a millimeter at our disposal and really, any other partial length that we can ballpark.

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To get going, make sure your depth jig is dialed near the middle of its' threaded length to give maximum flexibility of adjustment and set the machine up to a predetermined depth stop. Next, drill a few test holes and double check the setup. We are told that in days past, people have accidentally drilled all the way through the plate. During the first round, we drill to a single remaining thickness of 7 mm.

A few words about the pictures that follow. You will notice two different pieces of wood being worked. Both pieces go through the same process and so even when the pictures alternate between the spruce and the maple, the point of progress has not changed.

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The depth stop ensures that no hole is drilled that is deeper than 7 mm. As long as the wood is thinner than 7 mm, no hole will be drilled. At any thickness over 7 mm, a hole will be drilled and there will be precisely 7 mm of thickness between the bottom of the hole and the other side of the plate. It works. We do the same move to both the front and back plates. The next process is scooping out the wood until you reach the bottom of the holes. It is pretty critical to not go any deeper than the bottom. Just make sure to leave some little scars. Once the evidence of the holes is completely gone, you have no visual of how much "extra" wood you are removing. We use an incannel gouge, finger planes and cabinet scrapers, in this order, to gradually remove the interior wood and eventually make it look sorta pretty.

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The goal now is just to clean things up enough so that it is easy to do clean work on the final run of graduations. The final thicknesses of the top are supposed to spec out to between 3 mm and around 5.5 mm. This is when the templates come into play for the mandolin build. Concentric rings of graduations guide us in the areas that need to be thicker or thinner than average. Final adjustments are made according to a range of standards including flexibility, aesthetics and gut feeling.

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My teacher's teacher says that graduations are the single most important contributing factor in developing a nice voice in an instrument. As of now, the theory behind the graduations makes sense to me. How it came to be this way, however, is something that I want to know more about. The drilling jig gets adjusted a heck of a lot during this part. It's a matter of just turning the barrel of the jig a few degrees. Once you get a feel for the tools, it's easy to relax and just go to town; So I did.

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In the previous picture, you'll notice a pencil line depicting the oval sound hole. Inside of this line is a little ol' pilot hole drilled all of the way through. And on purpose too. Through that hole goes a tiny saw blade. Make with the back and forth and about 15 minutes later, you have yourself a rough cutout of the sound hole.

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Wood removal with the same tools as before is what follows. Though this time, the goal is to achieve as smooth a surface as you can. This is the time to polish your carve until it is perfect. It is frequently suggested to step away from a carving and come back to it later with fresh eyes. The cabinet scraper is an amazing tool and on this work, we are using the very thinnest one we own. It's like an airbrush for wood. Here they are, partners in crime. Almost there.

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That's about all I got tonight. Didn't mean to filibuster your time away. Hope you like it. Take care.

Tuesday, January 17, 2012

Like Peas and Carrots

The arching process continues to occupy my mando building efforts these days. I have been shaving off little slices of wood like this for months. MONTHS I tell ya!

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Seems like it would be tedious, but it really is a Zen kind of thing. As you would expect, the blueprint we are working from has exact dimensions specified for the contours, the thickness of the plates, everything. Once you forget about all of that and just go with it, it is a very pleasant experience to let the shape flow out. Put it this way; There are four of us building mandolins in this class and they all look different. Here's a look at the drawering...

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As of the start of my last class period, this is what the top of my instrument looked like. You'll notice lots of tool marks and plenty of rough spots but the arching work is obvious.

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At this point, I'm using two cutting tools to accomplish the arching. They are a tiny finger plane and a very thin cabinet scraper. The finger plane is fitted with a toothed blade that resembles a comb. It leaves us with less cleanup work than a straight blade would. Other tools that help keep me on track are my arching templates, my hands and eyes and a strategically placed full-spectrum light. The templates are renderings of the long arch and the side arch at the latitudinal and longitudinal center lines of the instrument. Boss Reed says, "they are guides, not gods". 'Nuff said. You just place the template on the instrument, mark with a pencil where the template touches the wood and then shave that wood away. When the template contacts wood along its' entire length, my boy, you have got it! (Lillian Gish.) Here's an older shot of the back plate with said pencil marks, a couple of finger planes and some of the templates.

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And here's the top plate, which is getting very close to being finished. Note the ramp that flows into the long arch. This is where the fingerboard will reside on the body and just past that will be where I cut in the sound hole. The angle of that ramp was created with a larger block plane. This is one of the parts that has to be perfect. No Zen moments here. It's all about clean work, constant checking of the progress and knowing when to stop.

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At the end of the class period, I gathered the two pieces for a team photo. Eventually, they will work together to feed a certain kind of hunger. They make a nice couple if I do say so myself. Soft and hard, plain and fancy and hailing from either coast. And each useless without the other. Ya gotta appreciate the contrasts.

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Tomorrow I will begin the process of creating the inside arches. Did I forget to mention those? Yes, more scooping, more shaving, and more scraping is in my future.

The crows are back, roosting in the park. They've brought friends this year and it is one eerie presence to behold. It's still warm enough outdoors for a walkabout, but it's late and I'm ready to get some shut eye. Sleep tight everybody.

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Monday, January 9, 2012

Arches of Gold, Zero Fat

Happy new year to all of you folks out there. The holiday season was a bit on the hectic side for me. The three weeks preceding Christmas saw me holed up in my shop/apartment putting some final touches on my first instrument built for a customer. In many ways, this guitar is a prototype, as it is completely custom designed. Building a Strat or Tele or other tried and true instrument is sorta like cooking from a recipe found in a magazine. All of the hard stuff has already been done before. Just follow the instructions and everything is likely to turn out fine. This guitar is a one-of-a-kind dish, made just for my friend Dave. I hope he finds it to be as tasty and compelling as I do.

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I just realized that it has been a couple of months since my last post. The lab time has been spent exclusively on arching the top and back plates for my mandolin. Arching is an exacting process. It is diametrically opposed to the Ike and Tina approach of starting nice and easy, and finishing rough. In the arching process we start rough. We use a scrub plane to remove the square edges around the oval-shaped plates. It doesn't have to look pretty and the work goes quickly.

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The second rough arching uses tools that are a bit more precise. An arching gouge a.k.a. incannel gouge is basically a scoop with a very sharp inside edge. A scooping motion is used, working across the grain of the wood, to selectively remove material from the edges of the plate. Gradually, you progress into the interior area of the plate, creating a slight, upward rising hill that approaches a plateau. This area is "hands off" for the time being.

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The arching gouge and a proper incannel gouge are shown along with the back plate of the mandolin.

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And so it goes. When the end of the class period arrives during the rough arching process, there is always huge piles of wood chips on the floor. The type of stuff you could let your livestock make a bed in. As we toil through the process, the piles become smaller and the shavings become thinner. The picky work uses finer, more precise tools and becomes less forgiving. While we use a blueprint and templates taken from an actual instrument, there is nothing like having the real thing in your hands to drive home the point that we are crafting a true work of art. Our maestro, John Reed, thoughtfully carried in the first mando he built with this system so we could have that experience. Here is another maestro, Mr. Jimmy Page, getting down on the same model instrument that I am building now. I can't wait to find a river bank to sit on and do my own getting down. Thanks for reading.

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