This is a technique I have used for longer necks. I'm demonstrating it on a uke neck because they seem less sacrosanct than guitars or violins. As such, people are ready to tackle a uke, patching together cigar boxes and plumbing parts with a vigor and profanity rarely administered to the noble guitar. Thhpt.
Basically, 1/16" thick slabs of wood are bent 14 degrees to make the head/neck transition. Then fiberglass is embedded in a rigid glue between the wood laminates. I use the urethane-glue-known-as-Gorilla because of its rigidity and availability. An epoxy would also do well here, but not necessarily better; it can be hard to find an epoxy of the appropriate viscosity, but Gorilla glue can be found anywhere.
This method eliminates the deadly grain run-out on the head/neck transition, which is the first spot a stringed instrument will snap when dropped or mishandled.
The fiberglass will handle most of the stress of the strings; this allows use of a lighter wood, creating a lightweight but extremely rigid neck, less fatiguing to hold, less susceptible to climate changes and ready for a lifetime of music.
Step 1: Description
A steel sting instrument is under more tension, so for those necks I bend the laminates (or "lams") and fiberglass to form the heel. Most woods do not easily bend that sharply, even in thin strips, so we'll avoid that chore for this relatively low-tension neck and build up the heel like a classical guitar.
Step 2: Making the Jig
A tenor uke has a 17" scale. I want to put the bridge in the middle of nowhere on the lower bout, which in this case is 7" from the neck joint. So there is 10" of neck before I hit the nut. I'll give myself 11" of neck on the jig before the head/neck transition, and trim off what I don't need. This uke will be a 6-string, so I'll need about 7" of head for the tuning machines; and one to grow on makes an 8" head on the jig.
Start by cutting two straight sections of 2x4s 20" long. Dampen a 2" side on one of the boards and run a bead of Gorilla glue down the center of a 4" side of the other. Clamp and let dry, scraping off any squeeze-out before it hardens.
Now cut a 14 degree wedge from the spine of the jig, 8" from one end. A miter saw makes this easy, but you can cut it by hand, too. For a triangle with two sides spanning two 2x4s (actual depth being 5") the short side will equal 1 1/4". Draw this triangle on both sides of the spine and cut carefully, watching both sides as you go.
Tape the acute angles tight against each other. Urethane glues excel at binding wood by the end grain-- dampen one side, apply glue to the other, then stand the jig upright, letting the tape act as a hinge and the weight of the 2x hold it in place. Let dry, scraping off any squeeze-out before it hardens.
Mark a line about 1/2" from either side of the joint. With a rasp, round the edge back to the line to make a smooth transition.
Step 3: Bending and Laminating
Spruce is light and strong, but poplar or bass would work well, and are commonly available at hobby and hardware stores. These woods will bend over the head/neck angle with little prompting-- usually wrapping a wet towel around the bending point for 15 minutes is enough to let you bend them cold. Even faster would be to use a hot pipe.
Prepare your Fiberglass cloth beforehand. You will need 4 pieces 4x19". Fiberglass cloth can be found at most hardware stores. The tidiest way I've found to cut it is to pull out 4-6 threads from the weave, then cut down the middle of this track. This ensures the cut is square, and keeps the long threads intact and in place.
You should also prepare your wood lams in advance. Scuff up the faces with 80 grit sand paper and pick up the dust with a damp rag.
The first lam in tacked in place with a small amount of rubber cement or white glue. With a scraper (I used a doubled-over piece of cardboard) spread a layer of Gorilla Glue on the first lam, wipe the bottom of the second lam again with a damp cloth, and press the two together. Spread a layer of glue on the top of the second lam, then spread the first piece of fiberglass on top, pulling out any wrinkles. Spread another layer of Gorilla Glue over the cloth. Dampen the bottom of the third lam, then lay it in place and immediately start spreading the next layer of glue.
Work your way up the layers in this fashion, ending with two lams without fiberglass between them. Press down at the head/neck transition, wiggling the lams to ensure they are seated. Clamp blocks over the neck and head. You want to squeeze just hard enough that a bead of glue appears along all the seams, but not so hard that you squeeze the glue out of the joints.
Clean your hands and work area with mineral spirits.
Step 4: Building Up the Neck
Pry the neck off of the jig. The first thing to do is to carve a taper into the neck. The Neck will be about 1/16" thinner at the nut than at the heal. This needs to be carved out of the front lam using a rasp, belt sander, or jointer. Carving it from the front lam also creates a sharp transition from the neck to the head, giving you a solid place to put the nut.
Build up a 2" x 2 1/2" block with solid wood or a stack of lams on the heel of the neck. Glue and clamp it so that the heel is about 11 1/2" from the neck/head transition point, let dry (scrape off any squeeze out before it hardens). Referenced from the front face, cut a 85 1/2 degree angle on the heel for an archtop, or a 89 degree for a flat top.
Now take a 3/16" slab of whatever you are using for a fretboard. Walnut, paperstone, ebony, whatevs. It needs to be 13" long and at least 2 1/4" wide. Cut one end square for the nut end and make a fiberglass sandwich the same way the rest of the lams were made. The square end should land right on the corner where the flat face of the neck ends and the head continues. Any mess made by the edge of the fiberglass or glue squeeze out will be covered by the nut. Clamp and let dry.
Step 5: Cutting the Profile of the Neck
Draw a line down the middle of the fretboard. This 6-string tenor is going to be 1 7/8" wide at the nut, so I'll make a mark at 15/16" on both sides of the line at the nut, and 1" on both sides at the heel. Connect the marks.
One of the most recognizable features of a stringed instrument is the shape of the head. Figure out something you like, or copy something you admire.
I like a slightly flared head. Cut the sides and place a tuner machine against it. Mark the centers of the tuning barrels, then draw a line square with the sides from edge to center. Moving the square to the other side of the head, draw a square line from the center crossing to the edge.
Hold the tuning machines in place and mark a reasonable space for them to work in. About half an inch, centered around the string hole, seems to do well. Drill a 1/2" hole at either end of the slot and cut out the rest with a coping saw and file.
Clamp the neck to the edge of the jig, and cut within 1/16" of the line. Use a rasp to get right to the line, keeping the face square to the fretboard.
Step 6: Carving the Neck
Draw a pleasing curve onto the heel and cut it out with a coping saw. I grabbed a cup and plate from the cupboard (I made this on the kitchen table) to draw the radii. Be as fancy as you want. A smaller radius at the base of the heel gives you a little more neck to play with.
Now flip your jig over and clamp it to your table. Clamp the neck in the crook of the jig at the head and at the fretboard extension.
Put the biggest, coarsest file in your hands and take a steady breath.
First rule of luthiery: If it looks good, it IS good. As you carve the neck, work methodically and along the entire length of the neck, alternating sides to ensure consistency.
Knock off the corners, turning them first into 45 degree angles, then knocking off their corners, until the neck is round. The layers will help; read them like a topographical map.
After the rasp, use 80-grit sandpaper, then 120, hitting the back, front, and sides of the head as well.
Step 7: Stretch Languorously
Just be methodical. Unclamp the neck when you think you're done, or if you feel stuck, and hold it like you're playing. Bar some cords and windmill and kick like no-one is watching. The carving will actually go rather quickly, and after you will wonder what all the fuss was about.
Fretting is an instructable of its own, and will soon be posted separately. You may have caught glimpses of the uke body that is being made for this neck. The building instructions for it will be posted as well. My goal is to offer an indestructible uke with clear, bombastic tone.
The neck construction technique is quite scalable; I've used it for a baritone guitar with a 31" scale. Please post any pictures of instruments you have made with this technique, and write any insights, tips, and improvements you might have.