Necks are pretty straightforward — since I use a non-adjustable CF neck stiffener, there is no real adjustment to be done, other than establishing the neck angle and installing the nut.
But necks are the hardest part to machine. There’s not a straight line on them! Or precious few, anyway. So after many, many tries, I have arrived at a process which minimizes tearout and keeps the parts adequately consistent.
First, a blank is glued up, and centered across the vises.
Next, the truss rod slot is cut with a 1/4″ cutter. This establishes the center axis of the neck, and from here on out, everything will stay nice and straight, including the fretboard and head block.
Next, a 1/2″ cutter is loaded, and the perimeter and slope are roughed in. By “rough”, I mean within 1/64″. Final carving is within 1/1000th of an inch. Here’s what the paths look like:
Same steps from another view:
Then a 1/2″ ball end cutter is used, leaving a perfectly smooth finish. It actually has scallops in it, but those scallops are only 5/10,000th of an inch tall. Hardly even visible.
Here’s what the machined part looks like at this point:
Next, the part is flipped onto an angled fixture, using the truss rod slot to index it centered and the base of the dovetail to index in the string axis. First the dovetail is cut:
Then the neck profile is roughed out.
Finally, back to the ball end mill to clean it all up. A little light scraping, and it’s good to go. The parts are so clean, I don’t even bother doing any cleanup until the instrument is assembled and in the white.
It takes a lot of code to get this all right. For instance, here’s what the neck volute paths look like:
But the whole neck machining process is under 1/2 hour, including tool changes.