Work from 11/11/08 through 12/4/08

The neck of a guitar is a pretty unique little piece of engineering.  About a quarter of the build time of the entire guitar went into some portion of the neck/headstock.  The neck has to be thick enough to withstand the stresses from the strings and not twist or bend.  Yet it has to be thin enough to be comfortable to play.  The neck also transmits some of the sound energy into the body, so the acoustic properties of the woods needs to be addressed.  It also needs to be adjustable down the road…  The fingerboard needs to be machined accurately so that the instrument plays in tune for it’s entire scale length.  The tolerances required are quite daunting.

Quarter-sawn Honduran mahogany and maple are the timbers traditionally used for steel string guitar necks.  Mahogany is tough to beat: It’s very stable.  Being even and straight grained and fairly soft it’s easy to carve into the complex curves of the neck.  It’s acoustically very sound as well.  Maple is stiffer and more stable, but tough to carve. To keep the woods similar on this guitar I decided to go with a laminated cherry neck to match the body.  Cherry also has mechanical properties that are similar to mahogany.  It’s not as stable though and may move with changes in humidity.  To help counteract this and stiffen it up I added a center spine of curly maple sandwiched by three layers of 5.5oz carbon fiber cloth on each side.  It also keeps with the black/white/black theme from the body binding.  I also used the best cherry I could find in my stack for the neck.  I used marine epoxy to laminate the neck.

After cleaning up any epoxy squeeze-out, I jointed the top surface straight and true on the jointer.  I’ll need to resharpen the blades soon: carbon fiber does a job on high-speed steel blades! I then cut the trench for the trussrod.  Virtually every guitar made in the last hundred years has a steel trussrod running down the spine of the neck.  They significantly stiffens the neck. Most are also adjustable and allow the neck to be put into tension or compression.  Put in compression it puts a reverse-curve in the neck and flattens it out. I used a dual-action one used in most Martin’s that is made by Gotoh.  I’ll glue it in later…

Traditionally the neck was attached to the top block of the body using a sliding dovetail joint.  Recently though most commercial builders have switched to a mortise and tenon joint that bolted together.  Two steel bolts run through the top block into meta inserts in the neck.  It greatly simplifies construction and is just as strong and acoustically similar.  It also allows easier removal of the neck if needed in the future.  I used the same system.  I cut the tenon in the neck and then rough cut the neck to shape.

The neck was then rough carved to shape using a straight spokeshave and my new rasp/file.  The file is pretty neat.  It’s cut so it takes a slicing cut.  It can be very aggressive like a wood rasp but leaves a very smooth finish like a file.  I guess they were originally made for working on aluminum car bodies. I heard about it through Lee Valley.  I modeled this neck on my Taylor’s.  I made cardboard cross sections of the neck at the 1st and 12th frets and carved the neck until was within a 1/16″.

The trussrod and the maple cap used to fill the remainder of the channel were glued in using epoxy.  I also drilled for and set the bolt inserts in the tenon.  To eliminate any chance of splitting, I drilled the holes for the inserts over-sized and set them with thickened epoxy.  I had drilled the holes in the top block before putting the back on the body.  When cured the cap was trimmed flush with the top and the neck was then fitted to the body.  The fitting ended up being almost a two hour process.  First I drilled for the bolts and trimmed the tenon so the neck slipped in snugly.  With the neck bolted to the body for the first time I checked the neck angle.  The neck doesn’t meet the body at a 90? angle… it’s more like 88?.  If it was 90 the strings would be flat against the body and it would be unplayable.   There’s a specific method of checking the angle…  Mine was too steep. It took 90 minutes of fiddling to get the angle right and the neck-to-body joint super tight.

With the angle set I trimmed the heel of the neck to length.  To cap the heel I glued on a piece of ebony and sanded it flush.  Once the neck was attached it would be hard if not impossible to finish sand the heel area so I did that.  Finally I permanently attached the neck to the body using a little bit of regular wood glue at the neck/side joint and torqued down the two bolts.

The ebony fingerboard was trimmed to size/shape and attached using wood glue, a shaped caul and plenty of C-clamps.  I decided to buy my fingerboard with the frets already cut and the top already radiused.  To have any kind of playability it is imperative that the slots for the frets are cut accurately.  I went with a standard Martin 25.4 scale length (actually 25.34″) and radiused to 16″.   I trimmed the neck to the fingerboard after the glue has cured and did the final sanding on the neck.

I’ll write up a seperate post detailing the headstock and the inlays…