Making Your First Guitar
A Tutorial
Routing Body Cavities
In both styles of guitar, it is necessary to route out some cavities in order to accomodate various components of the instrument. Both will need some place to insert the pickups as well as an electronics bay for the volume and tone controls, switches and an active circuit board with a battery if making an active instrument. The bolt on neck will also require a pocket in which to insert the neck for secure attachment to the body. These operations are best done by a router, although they can be drilled out and cleaned up with chisels, or just done wih chisels alone. The other alternative is to simply route out a large cavity and cover it with a pick guard plastic laminate. This allows you to be less neat and precise in your routing, or hollowing, by whatever means you have, and yet once covered with the pckguard, it will have a neat and professional appearance. This will also decrease the weight of the instrument to make it more comfortable, but be aware that if the body is made too light, the left hand (arm) will always be fighting against a heavy neck and be pulled by gravity towards the floor. Keep the guitar's balance in mind.
Routing is best done while the body is still "square" and not recessed or contoured. This allows the template to be attached to the body securely by means of duct tape or a screw into an area which won't be seen or will later be removed itself. A flat uncontoured surface obviously will hold the template flat and without rocking, much easier than an arched top, etc.
This is because a template is made of the shape of the cavity to be made and a template collar is attached to the bottom of the router which will follow the edge of the template and cut out the hole exactly. This can be done with an appropriate size collar and router bit (depends on manufacturer). The template is larger than the actual cavity being cut as it must accomodate the width of the collar as well. I like to make my templates from masonite board or thin plywood.
Masonite is easily cut with a jig or scroll saw or even an X-acto® knife and cleans up easily with sandpaper. Try practice cuts on scrap wood to both check and adjust the side of the cavity to ensure an accurate cut for the pickups as well as to get a feel for the cutting action of the router. Move the router so that the direction of travel is with the cutter bit spinning into the wood. This gives a cleaner cut and better control. Don't make cuts too deep as this will put quite a bit of stess on your tool and won't produce as nice a cut. Make several passes lowering the bit into the wood, say, a quarter inch at a time, until the required depth is reached.
Again, one can route a large cavity and cover it with a pickguard, but a slightly oversized hole to accomodate the pickup and then use a pickup "ring" to cover the edge of the cavity. Or, be very precise and meticulous to get a cavity the same size as the pickup with just enough clearnace for unobstructed movement for height adjustment. The pickup ring is most popular with humbucker style pickups. Routing a cavity for a precise fit takes full advantage in showing off exotic wods and interesting grains. You don't want to spend big dollars on exotic woods and then cover them up with plastic pickguards. When making these precise cavities, keep in mind what finish you intend to apply to the guitar. Finishes high in solids content which tend to build quickly may add enough material (finish) that a freely moving pickup in a cavity now sticks and binds, or worse, won't go in at all. You can fill the cavity, but this might chip the finish on the body when you try to remove the "plug". You could make the cavity just slightly larger so that the finish will spray on to make the cavity just the right size when finished, or you could clean up the rim of the cavity back to the wood using a Dremel® tool and an appropriate bit once the finish is dried and cured. Depending on your finish, this may or may not be a problem. Nitrocellulose® lacquer builds quickly to a deep finish and may add a sixteenth of an inch to your dimension, or an oil finish which will soak in and leave a barely perceivable layer.
The electronics bay can be covered by the same pickguard from the front, or a cavity can be routed in the back to within an eighth of an inch from the top surface. Holes can now be drilled into the body at the positions of the various components, such as volume and tone controls, as well as. switches. This is best done from the top surface down with brad point bits to minimize splintering when the bit breaks through.
Cavities are joined together by using a long drill (to get a better angle and keep the chuck from marring the instrument surface). At the side of the cavity where the pickup wires are, join the pickup cavities to the electronics bay. Drill a hole to add a ground wire from the electronics bay to the metal bridge or tailpiece in order to ground it as well. With modern shielded pickups, this may not be crucial, but I figure that as it doesn't hurt, do it anyways to be safe. One way to join up the cavities is to drill a hole straight through from where the strap button will go on the body. Once connected up, this hole can be plugged with a hardwood dowel of matching wood and when the strap button goes on the finished guitar, it will hide the plug altogether.
Route a lip around the electronics bay cavity the thickness of the material to be used as a cover. This provides a neat professional appearance to the instrument and prevents snagging by clothing and such.
