Sunday, July 8, 2012

Archtop Guitar - Finger Rest / Finishing part 2

The finger rest was easy enough to make but very hard to fit to the guitar.  The plans call for the guitar neck to have a set back angle and have the strings sit a predetermined height above the top plate at the position of the bridge (between the two central points of the "f-holes."  I made sure of this when I made the neck but one thing that I did not take into account was the thickness of the neck where the finger rest attaches.  This has to be thick enough to accept the mounting screws but also has to be high enough so that you can get a screwdriver in to seat the screws.  Lastly the finger rest has to hold a pick up at just the right distance from the strings.  I made a small wedge for the pickup to mount on and checked all of the distances.  All of my geometry was spot on but I was a little too tight to the top plate to get a screwdriver in.  This is why I took a few weeks away from the project to think this one over since no solution came to mind right away.

To further make the matter more difficult, the finger rest sits parallel to the strings but must sit low enough so that it doesn't interfere with playing, yet sit high enough so that you can use it as a "rest" for picking.  Lastly the finger rest does not sit on the same plane and the strings but is canted down from the strings across the body of the guitar. 

I made the finger rest out of ebony, with a mother of pearl inlay that goes well with the fret markers and tail piece inlays. I mounted a couple of tuners to the head stock and the tail piece and bridge so that I could string up low and high E strings to get the geometry for the finger rest.  I then made an ebony block that would attach to the bottom of the finger rest and mount the assembly to the side of the neck.  Two holes were drilled into the mounting block and corresponding holes were bored into the neck.  To get around the low placement I used allen head screws.  These allowed me to use a small allen head wrench that fit perfectly into the space provided and made for a very nice fit.  Problem solved!

Next I did something that you are not supposed to do.  I strung up the guitar with all of the strings and played it for a day.  The action was surprisingly good considering I did no set up work and the  guitar sounded great acoustically but I quickly found that the neck was too chunky and "square" from frets 4 to the nut.  This is something that I did not appreciate when I was forming the neck but when I re-checked with a pattern guide, there was a subtle difference in neck geomertry between the Laravee neck and the archtop.  They say you should not play the guitar because you will get oils into the finish that may prevent the lacquer from properly bonding but I was planning on applying more layers of shellac so I knew this would not be an issue.  I am very glad I did this because I would not have been happy with the neck otherwise and I learned that for a beginner like me, there is a difference between feeling the neck without strings and playing it.

This is the finger rest.  The hole is for the volume pot and the slight depression in the back is to allow the screw head clearance when inserted.

Next I cleaned the guitar and sprayed several coats of shellac, especially on the neck because it had need sanded bare in the areas that were re-worked.  Any small imperfections were repaired and 10 coats of lacquer were applied over three days with my new spray gun.  For the previous four stringed instruments I used spay cans of lacquer but for this guitar I decided to get a spray gun and try it out.  By my quick calculations, the gun should pay for itself over the course of just a couple of guitars (that is if you already have an air compressor). 

My spray set up consists of a spray booth that exhausts to the outside and a "door jamb" style spray gun.  This gun is powered by a 5 horse compressor in the next room that feeds its pressure line "up hill" to a water trap.  The "up hill" run allows condensated water to drain back to the compressor and the water trap is extra insurance.  A coiled pressure line runs to a quick connector that attaches to the gun and the gun hangs on a screw when not in use.  I found that around 20 psi worked well for the cut shellac and 25 psi was good for the uncut lacquer.  More pressure resulted in more over-spray and a pebbled finish.  The liquid feed was opened up to make an oval spray pattern.  The gun was easy to clean and did not require cleaning between coats but only at the end of production.   Here is the set up.

Now to let is sit for a couple of weeks while the lacquer cures...