Wednesday, June 20, 2012

It's All In The Execution

 I am now in the process of setting the neck to my mandolin build.  This employs a not-very-large mortise and tenon joint to connect the neck and the body.  This ancient builder's joint will live it's life under a great deal of string tension. Thus, it must be fashioned without errors.

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The pace in the classroom lets us crawl to the destination.  This way, we will have an undiluted sense of the precision work that is required to achieve our goal. It feels to me like I'm learning an elemental secret. The mortise and tenon predates Twitter, omelets, and Stonehenge. I cannot call it anything but a deep lesson to the learner.

 Mortise and tenon joint

The overall dimensions of the heel have already been crafted.  The only variable here is the total height of the heel.   That dimension can be accurately figured by measuring the box from the inside surface of the button to the top line of the soundboard.

Chalk fitting, one last time, will reveal the minute imperfections that are preventing full contact in the joint. It's like an X-ray in that the chalk allows us to see things that aren't always visible to the naked eye.

We trim only the inside of the mortise. It's a good idea to use chisels that are very sharp. The heel angles have already been cut. So we chalk up the fitting area of the tenon (heel) and cram it into the mortise. Then we pull out the neck and look for the white spread of the chalk.

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The chalk clings to the high points inside the mortise. They are reduced with a slicing motion from our chisel. More chalk, more fitting, more slicing.  When the heel hits the button and fingerboard is still above the body, it's time to trim the heel. We use a Japanese razor saw for this and take off about two millimeters at a time.  Then, back to chalk-fitting.

Eventually, trimming the heel with a razor saw becomes trimming the heel with a block plane, taking off slices that are thinner than paper. And then, at some point, everything just fits perfectly.  It's impossible not to smile when then happens.

Before gluing the neck in, I am going to go ahead and inlay the Lowstrung Guitars logo into the headstock overlay.  The simple, two-piece design uses mother-of-pearl and Abalone shell. I cut the pieces out with a jeweler's saw then file the edges until they are smooth and the curves fit together. Next, I mark the location of the inlay on the headstock.

To keep the work clean, we trace the inlay shape with an X-acto knife.  Then we grind a little chalk dust into the finely scribed line.  The tiny white line show up really well on the black wood.  We use a tool that is similar to a dentists' drill to remove the wood from inside the lines.

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Once the inlay fits well, super glue and ebony dust are used to hold the pieces in place.  A little sanding levels everything out and... presto! Instant logo inlay. 
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My teacher, Mr. John Reed, likes to say that the neck should look like it just grows right out of the body.  No gaps, no wiggle, and your should hear and feel a nice groan when the pieces are fitted together.  Once this is all accomplished, it's time to glue up.

Of course, it's smart to dry clamp several times to be positive that it all fits together perfectly.  Once John gives the go-ahead, all you need are an extra pair of hands, a tiny bit of hot hide glue and a single Jorgensen clamp.
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I mixed those ingredients on a Thursday night which meant my glue joint would have over 96 hours to cure.  The following Tuesday, I removed the clamp and had a "one-piecer" on my hands. Sweetness. Another bit of good news was that it was time to carve the neck, which is one of my favorite steps.  And one of the most character-defining.

Hand-carving a piece of wood can be a wonderfully organic experience.  A sharp knife in the right hands makes a fantastic sound.  It is much like a singing voice.  Steel and the knowledge to use it become an irresistible force and the wood sheds a song as it is crafted to the desired form.
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We begin by carving the button. Once it is finished, we take cues from it that guide other dimensions on the neck.  We draw guide lines onto the neck.  These let us get into the work without going too far.  When we reach the boundaries of the lines, we modify and refine them to bring us closer to the finish line.
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When the button is finished, I am able to install the binding to the back of the instrument.  This goes in just like the top binding did, but terminates at the button.  The fit and finish is then manipulated to make the intersecting components look like one cohesive whole.

The neck carving process continues in the same way using progressively finer and finer tools.  Moving from knives and spoke shaves to files and finally, the amazing cabinet scraper.   We can skip the final sanding of the instrument altogether if we are diligent enough with the scraper. Properly utilized, the scraper leaves a finer finish than sanding as there is no dust to be pressed into the pores of the wood.

Here's the proof of that.  This beauty is ready to be fretted and to receive a final going-over with the cabinet scraper.  Then it's off to the spray booth!
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Until next time...

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