Moving on: Weeks 9-11

I've been having a hard time keeping up with this journal due to the arrival of homework for my fluid mechanics class.  May be a little over committed on the education front right now.  This entry will catch up over the last three weeks of finishing off the body by installing the bindings and setting up the neck and fingerboard.  We've also begun finish sanding the bodies.

Top and  Bottom  Bindings

In preparation for laying in the bindings, the excess top and bottom wood overhanging the sides was trimmed off with the router using a flush bit.  No special jig is required, as this operation is just in preparation for routing the ledges for bindings and purflings.

Once the excess was removed, a ledge was routed for the binding.  Again, a straight, downward spiraling bit with a guide was used to create the ledge on the top and on the back.





On the bottoms, I am using the koa wood binding by itself.  It is installed with yellow wood glue.Here is a different guitar set up for the installation of an ivroid plastic binding along the bottom ledge.   The two pieces of the binding are squared off to create a clean joint at the neck end of the guitar.  One side is glue most of the way in and then trimmed to meet at the center line under the end graft.  The second piece can then be laid in and trimmed for the cleanest joint possible.

For my top, as well as the koa binding I'm also using a decorative purfling strip.  In order to install the purfling, an additional shallow ledge is required.  Here a second router is adjusted to the correct depth with a bit offset from the guide to match the width of the purfling strip.  This creates a "staircase" ledge.  As usual, the router gave me some trouble and I ended up with a deeper secondary ledge.

This provided the opportunity to use a slightly thicker purfling with an extra color band through it.  It happens that this  additional band is koa and so matches my guitar well.  It also has some consistency with the elaborate rosette that I ended up with.  The picture to the right shows both the purfling and the staricase ledge for the binding and purfling.

	I worked at home to finish installing the purfling and binding.  This is an operation that requires a considerable amount of masking tape.  The challenge on this operation is to glue in all four pieces, 2 stretches of purfling and bindings each, in a single operation.  To set up, masking tape is laid out in 1 inch intervals.
I was fortunate that by working at home I would have the skills of the new master luthier in the family.  Still, getting all of the pieces laid down and then 'clamped' in by the tape within the 5 minutes of open time allowed by the glue was a challenge.  One advantage of working on the top is that a joint is only required at the butt end by the graft.  The neck end does not have to meet as it will be covered
	by the neck and fingerboard. Here's Jonah showing off our work.  Kind of reminds me of a post-operative patient from a nose job - can't see the results until the bandages come off.
Here's the patient without the  bandages, ready to go back to the shop.  I have a few narrow gaps between the top and the purfling strip, generally less than 0.5 mm that I'm in the process of filling with a mixture of sawdust and glue .

Neck Setup

This picture shows the neck and fingerboard blanks that we are starting with along with Edward's new jig for figuring the angle of the neck with respect to the sides.  This is never exactly 90 degrees, so this joing helps to set a horizontal line along the top, matching a tangent to the slight curve of the top.





As you can make out in the photo to the left.  A small amount of clearance, about 9 millimeters is left between the bottom of the finger board and the top of the guitar at the bridge.  The fingerboard will actually dip down slightly when it is glued on.  My neck angle did not require adjustment.  Using this jig, however, does allow for slight increments to be identified on the front of the neck blank to be removed in order to get the tight fit with the body.  material was removed from the front by sanding it against a circular sander using a thin wedge to change the angle of the neck.

Once the neck joint was put in the correct plane, the holes in the neck block were used to identify the location of the two bolts in the neck.  These were drilled out and self-tapping insert installed for receiving the end of the neck bolts.

 

Fingerboard

 

The fingerboards we are using come set with a scale length of 25.4 inches (the length of the first octave from the nut to the twelfth fret).  The blanks for these are rectangular (see example on LMII) and must be cut down to the proper shape.  The fingerboard tapers up from approximately 1.75"/ 45 mm at the nut up to 25 11/16"/59 mm at the 20th fret.  Here is my fingerboard cut to those specification.  Two lines are marked at the 14th fret which marks the division between the body and the neck.

A centerline has been drawn down the fingerboard to match the centerline of the body which has also been extended down the neck.  A small wire brad has been used to pin the fingerboard to the neck at the 13th fret (small white circle in the photo) and another one at the 1st fret.

 

Bridge

 

Setting up the bridge is one of the most important steps for getting the guitar ready to play.  The bridge must be centered property and the line created by the bridge saddle must match the scale of the fingerboard to ensure the guitar is tunable and playable.
With the fingerboard set in place, the bridge can be aligned from top to bottom using reference lines off the sides of the fingerboard.  Two long straightedges are placed along the sides of the neck and their center is checked against the centerline of the body.  The bridge is centered between these two straightedges and the side positions marked with masking tape.  The bridge can then be moved along the centerline between these pieces of tape.


Using a thing ruler laid in the tweflth fret to define the location of the first scale, the bridge can then be offset vertically from this location.  Theoretically, the distance from the 12 fret to the bridge saddle, a second scale, should be equal to the first.  This distance is increased slightly, a technique known as compensation, to allow for the
depression of the strings and for eventual compression of the guitar due to tension along the neck and body by the strings.  In the case of this project we are compensating by an additional 2 millimeters at the 1st string (high E) and 4.5 millimeters at the 6th string (low E).  Different tunings or string types would affect the amount of compensation used.  With the bridge in place, two holes are drilled through the 1st and 6th string holes, the top, and the bridge place to permanently place the bridge; although it will not be glued on until later.

 

Truss Rod set up

The neck of a steel string guitar is supported by an adjustable truss rod that serves to counteract the tension placed along the neck by the steel strings.  The truss rod (here is an example from LMII) runs from the headplate through the neck into the body of the guitar where it ends up close to the transverse brace.  In order to insert the rod, the groove is routed out using the jig shown at left.  The jig is aligned at the neck joint and along the centerline of the neck.  A plunge router is used in two or three passes to rout the groove out to full depth.




As we switch to working on the neck, we're also sanding down the bodies in preparation for finishing.  The first sanding was with 120 grit paper; this removed excess glue and any major irregularities in the surface of the wood.  My top is light enough that this sanding was sufficient for developing the final tap tone on my guitar.  Some tops are sanded down a few more hundredths of an inch along the bottom and outside edges in order to increase response, especially in the bass range.  I've also started to fill some small gaps with a mixture of sawdust from excess pieces of spruce or walnut to fill gaps along the binding and purfling.  The next sanding will be with 220# as a final step prior to finishing.