Body

Once you've finished your design, transfer it to the top of your board. Because I do not have a planer and I consider the flatness of the neck to be one of the most significant parts of the instrument, I drew my design so that the flat surface of the neck (which is later glued to the fingerboard) is the face of the 2x4. I then angled the body slightly to make up for this.

Using a band saw and/or coping saw, carefully carve out the shape of the instrument. Leave a little extra room on each side of the fingerboard - we will later sand the neck to size with the fingerboard attached.

Then flip the workpiece on its side and draw the profile of the instrument. Cut it out with the saw. (Keep in mind the radius of your bandsaw - I knocked the blade off track at least 2 times while trying to make a tight curve. Later I just used the coping saw to clean that bit up.)

Now is also the time to drill the holes for the strings/pegs. For my design, I drilled 4 holes in the head to hold the ball-end of the strings (note that this is reverse of how a traditional violin is strung). I also cut a small channel on the bottom of the head so the balls don't protrude. Change drill bits and drill holes for the tuning pegs behind the bridge.

Neck

To make the shape and contour of the neck, I turned to my knife. If I had a dedicated wood carving knife, I would have used that, but all I had on hand was my trusty opinel pocket knife. Overall it worked pretty well, although that thing does have a thin blade which made some of the shaping a little more difficult. Careful with splintering - I don't do much carving so I don't know if this is a normal thing, but several times I was whittling an edge and seemed to catch a splinter that just got bigger and bigger until it took out a chunk of wood exactly where I didn't want to.

After the knife, I used a file/rasp to tidy things up a bit.

In order to finish the shaping of the neck, we need to attach the fingerboard temporarily. Using a small amount of glue (we will be removing the fingerboard in a minute, so don't go nuts) attach the fingerboard to the neck and clamp it. Let it set for a bit then use your sander to trim down the edges of the neck until it is flush with the fingerboard. Remove the fingerboard and don't forget to sand down the glue left on the underside. Remove the fingerboard once you've made the sides of the neck flush (I used a chisel and carefully wedged it).

Drilling

Two things must be drilled - holes for the strings at the top of the neck, and holes for the geared tuners near the chinrest. I don't have a drill press, so things weren't perfectly aligned, but it's not so far off that it really bothers me.

For the small string holes, I used the smallest bit I had.

For the tuner holes, I ended up using a 9.5mm brad point bit, which was just slightly too small. I was able to eventually (and with great effort) get the tuners to fit through the holes, but it would have been much better to use a 10 or 11mm bit. When drilling, try as much as possible to make the holes at a 90 degree angle to that part of the work piece. You want the gear box to sit flush beneath the wood.

Sanding

You know what to do. Start low and work your way up. I started at 60 and for most of the instrument didn't go higher than 150. I mean, it's only a 2x4.

For the neck, I went up to 600. Your hand spends a lot of time moving around the neck so it only makes sense to make this part as comfortable as possible.

Finish

I decided to use a traditional clear finish on the neck and paint for everything else with black spray paint.