Weeks 12-13: Neck work

This post covers another two weeks of work in the shop - pretty much all on the neck now.

Roughing out the Neck

Prior to gluing on our fingerboards, which we previously trimmed down to the correct widths at the nut and 14th fret (where it will  meet the body), we cut down the neck blanks to the size of the fingerboard.  This was done on the bandsaw after the lines defining the top and bottom edges of the fingerboard on top of the neck were transfered to the back.
The headstock shape I'm using is based on a classic Guild headstock, like the guitar I've had since I was 16 (a late 60s or early 70s Guild D-35).  I traced that design as best I could, but then had to work it down to a slightly smaller size to fit the material  I had.  I had to join up two pieces of the extra walnut from my back and sides to have a piece large enough to glue on for the headplate, and this became a limit on the size of my design.  The design was rough cut on the bandsaw and will be finished by some combination of a rasp, file or sandpaper.

Gluing on the Fingerboard

The fingerboard position has been kept in the correct position by a couple of pins that were inserted at the 1st and 13th fret.  The truss rod was also glued into the neck groove we did in the previous class at the same time that the fingerboard was glued on to the neck.

The glue up is straightforward with a generous amount of glue laid into the groove for the rod, and then all over the neck.  The fingerboard was held in place with a long caul so that clamping pressure was even across the length of the fingerboard's edges.

Inlay

The only inlay on this guitar is for the fingerboard dots at the 5th, 7th, 9th, 12th, 15th and 17th frets.  Two dots are used at the 12th to designate the octave.  The dots I used are mother-of-pearl with a 5mm diameter.  The inlay just requires marking a center position and then using a hand drill to make a shallow hole for the dot.

Each dot is set with some super glue.  Then all of the dots and the fingerboard were sanded.  I still need to go over mine one more time with som 00 steel wool. There are some small dots put in with plastic along the top of the fingerboard as well.  These holes were made on the drill press, then a small plastic stick was inserted in the holes and cut off.

 

 

Frets

The fingerboards we are using were fully serviced before we got them: a radius had been applied and the slots for the frets were pre-cut.  Our job is just to install the frets.
We're using standard nickel-silver fret wire.  Each fret is cut a little long for the slot and then hammered into place with a 'dead-blow' hammer that kicks back very little.  Each fret is tapped in at the top and bottom so that the tang grabs into place.  Then a series of taps from the middle out to each side sets the wire fully into the slot where it is held by the tang.




After the frets are installed, they are trimmed to length with a pair of nippers.  A small straight edge is used to check that none of the frets are sitting
higher than the others.  Any found to be proud are given some extra taps to set them in deeper.  Then a mill file is run along the edges to dress and clean the frets.  The file is held at a 60 degree angle in order to create a bevel .  Each fret can also be dressed with a small file to create a slight horizontal taper at the ends.  Out necks our now ready for carving.

Finishing

We have also begun sealing the top, back and sides with a couple of coats of thinned shelac (a 50-50 mixture of shelac and grain alcohol).  The top was sealed first in order to keep any color that might leach out of the sides from getting into the lightly colored spruce.  This can be a significant issue for rosewood, but didn't seem like a big problem for the walnut I  am using.

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.