I've been meaning to have a proper attempt at this for a while - all of my previous builds have used a straight neck and to be honest there's nothing at all wrong with that. A 3 or 4 string guitar doesn't really need a taper in order to be playable. I do however think a tapered neck looks more elegant, and it does feel nicer to play. I believe this would normally be done with power tools such as band saws and disc sanders. I try to do everything with hand tools. Here's how I did it:
(My usual disclaimer applies: I am by no means saying that this is the only way to do this, nor is this entirely my thoughts or my research. I consider everything I do a collaborative effort with everyone else in this community)
Another important consideration with job is the order in which these steps are taken - there are some steps which need to be taken whilst both the fretboard and the neck are still square and true - I can't imagine trying to mark or cut the fret slots after the taper! I suppose one could use a bevel gauge but I don't have one.
So, to begin with, I measured out the fret locations in exactly the same manner as I always do. I also marked the centre line down the fretboard and marked the locations of the marker dots.
I made a couple of calculations at this point about string spacing. The neck blank was 42mm wide, so with a 12mm string spacing at the bridge there would be 3mm clearance from the string to the edge of the fretboard at either side (12+12+12+3+3=42mm). I decided to go with an 8mm spacing at the nut, as this is what I have on my 5 string banjo and it seems to work well. Therefore my total fretboard width at the nut would need to be 8+8+8+3+3=30mm I made a solid pencil line connecting the 2 points all the way down either side of the fretboard.
I decided to cut the fretboard to shape before gluing it to the neck, so that's what I did next:
To do this I clamped the piece to my bench and used a Surform, then a block plane, then a file, then 80 grit sandpaper to get right up to the pencil line. I kept sighting down the line and lying the piece on a flat surface to check for consistency.
Once I was happy with this I glued the fretboard to the neck and left it clamped overnight. Once the glue had set it was time to start shaping the neck blank to fit the fretboard. I had a couple of ideas on how to approach this, but in the end I used my #2 and #4 Continental hand stitched rasps. They remove material quickly and accurately. If you try this with a crappy cheap rasp it may end in tears.
I clamped the piece to my bench and carefully removed the wood from the neck to match the pencil line on the fretboard. Once I was happy with it I switched over to a flat file, then to sandpaper to smooth out the surface. At this stage I clamped the neck so it was sticking out from the bench so I could easily sight down it.
The process of shaping the neck by hand took over an hour, so it certainly adds time onto a build. The following day it was time to shape the back of the neck. I am a lot more well versed at this so it was a little quicker. It was slightly trickier than shaping a straight neck, however.
As usual I used a spokeshave, rasps, files to do the rough shaping, then moved onto a long strip of 60 grit paper across grain (shoe shining style). Of course after this make sure to sand over everything with the grain so as not to introduce unsightly scratches. It all turned out pretty well:
The next step was to move on to installing the frets, which was pretty much the same process as with a straight neck, only you will need to cut the fret wire at different lengths to fit the width of the neck.
I think it turned out pretty well!