Shaping the neck
The shape of the neck is a matter of personal taste. The neck should be comfortable to hold for the player and not be too “fat”. Perceptions of what is “comfortable” may vary from player to player. There are basically three different neck shapes : (a) ovalshaped, (b) V-shaped, and (c) U-shaped ones. And why not make an asymmetrical neck, in particular if this is considered more “comfortable”? The shape of the neck could even change along its length, from the first fret to the last. Everything that improves playability should be welcome. A thin neck is, however, more likely to bend, whereas a thicker one will give more stability and a longer sustain. If you have no idea of what neck shape to choose, I recommend that you try an oval-shaped one. With a spokeshave you can always make changes to it later, if necessary even after finishing.
After you have made up your mind about the shape of the neck, I recommend that you cut out a negative of its shape in three positions and that you use these templates to check the curves of the neck.
Mark the point on the neck from where it is to stick out of the body (2). Draw a curved line about half an inch away from this mark as shown in picture 3. Now draw a center line on the back of the neck (4). Then shape it from that point so that it gradually turns into a flat area where it will join the body.
The best tool to use for shaping the neck is a spokeshave. To enable you to work in a comfortable position the neck should be fastened sufficiently high in relation to your body and so that it is higher at its body end (as shown in picture 5). If your neck has a Fender-style peghead, fasten it face down on a jig. A neck with angled-back peghead is brought into a comfortable working position by clamping its head to the edge of the workbench (5).
Using a spokeshave a chamfer is now planed between the area where the neck leaves the body and the beginning of the peghead (7). Start by planing the edges at 45 degrees. Change the side you're working on regularlay to ensure even progress is made on both sides.
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Then plane further chamfers as required to get the desired neck shape (1). Do not make the neck thinner at this stage or take anything off the sides of the fingerboard.
The transition into the flat area where the neck is made to join the body (2,3) and the transition into the peghead are roughshaped with a wood rasp and a scraper (4,5).
Later, the neck can be made thinner. Do this very carefully, making sure that the neck becomes evenly thinner towards the nut and is exactly as thick as wanted at the first fret. Leave at least 3mm (1/8") of wood over a straight truss rod at the nut. If the truss rod was fitted curved, leave 3mm (1/8") of wood over its highest point. Always check and measure how much wood has already been taken off (6). I once had a rendezvous with a truss rod at this stage, which I wasn't very pleased about, and I guess you wouldn't be, either.
Use the templates from time to time - as shown in piture 7 - to check your progress (i.e. if the desired neck profile has been reached).
After the neck has been rough-carved with the spokeshave continue with a scraper (8) and clean up the transition between the neck and the peghead as well (9). Always work in the direction of the grain. As a cat wants to be stroked in the direction of its hair, wood also “wants” to be treated this way.
Unclamp the neck at regular intervals and inspect it by turning it in different directions to find out any irregularities (10). It is very important to inspect the neck at different angles against the light. Also feel the neck with your fingers to find out any areas which still require work.
Finish off with 80-grit and 120-grit sandpaper, sanding the neck in a shoe-polisher-movement (11) until the wood is evenly rounded over the whole length of the neck. From now on sanding should only be done in the direction of the grain. Check if the back of the neck is straight by laying up a straight edge (12). Take your time and continue sanding until you can see no more irregular areas or scratches on close inspection of the neck (13).The neck is now finished for the time being and can be put to one side (14). If any irregularities should be found afterwards, they can always be corrected later.
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Machine-sanding the neck
Most guitarbuilders do all the neckshaping with a belt sander. When using a belt sander the curved parts in the area of the neck-body-joint and towards the peghead are sanded with the freely-accessible end of the sander. For this kind of work it is essential that you provide for reliable dust collection. A belt sander is a simple power tool and building one yourself therefore quite conceivable.
However, I personally prefer shaping my necks with a spokeshave. This is a very quiet tool and does not produce any dust.