The neck pocket routing template is for solidbody guitars with bolt-on necks. There are two template sizes included: the smaller shape is for guitars, and the larger one is for basses. Both the guitar and bass routs are shaped for necks with radiused heels (Strat, Jaguar, P-Bass, J-Bass). The guitar rout is not intended for use with Telecaster necks (which have a square heel).
Draw a centerline on the workpiece. On this centerline, measure the length of the neck pocket and mark that point. Align the template to that point and use a sharp pencil to trace its neck pocket shape onto the workpiece.
Don't try to cut the depth in one pass
The depth of most neck pockets is 5/8". Trying to cut to this depth in one pass is not practical—it is risky and difficult to control. Using your 1/2" cutter, the maximum depth you should cut in one pass is approximately 1/4". This means cutting the pocket will take three or more passes.
With the cutter bit raised for a 1/4" cut, the ball-bearing will be also be raised above the surface of the wood. You'll need to raise the template on shims to meet it. The template should be centered and clamped above the workpiece on 3/8"-thick shims. The shims put the bearing in contact with the template while the bit makes the cut below it. A ruler, or any square-cornered object, will help you align the raised template with your line on the workpiece.
The template is oversize
The template is oversize by approximately .040" to allow for variations in neck width and finish thickness. Compare your neck's heel to the template, and measure the gap with feeler gauges. To rout a smaller neck pocket, reduce the template size by adding a few layers of masking tape. Check the fit of the neck within the template until it is snug.
Remember, the finish will add thickness
A typical neck finish is about .004" to .006" thick. If you're working with unfinished parts, keep in mind that you don't want any finish build up in your neck pocket so mask it off before spraying. Any overspray in the neck pocket should be carefully sanded back once the finish cures.
Rout in a series of side-to-side passes
Start the router bit at the treble side and cut across to the bass side. Rout the pocket with a series of treble-to-bass passes, cutting flush to your pencil line on the sides and end (reverse for left handed guitars).
As you set the router for a deeper cut, the bearing will drop below the template and lose contact with it. It's not necessary to lower the template shims; instead, reposition the bearing on the cutter shaft by using pieces of tubing as shims. (Cutter bits from Stewart-MacDonald include heat-resistant tubing for this purpose.) A short length of tubing positions the bearing, while a longer piece keeps it from riding up toward the router. Leave 3/4" of shaft exposed so that the router collet can grip the bit securely.
Tip: Many builders prefer to use extra bearings on the shank. With a stack of four bearings, the cutter bit contacts the template at all heights.
After you've gained enough depth for the bearing to contact the newly-routed neck pocket, the bearing will guide on the wood itself.
Creating a larger pocket
It's rare for a neck to fit too tightly in the template, but if it does, you can create a wider neck pocket by cutting oneside first, then moving the template to cut the other side. Position the template away from the centerline equally on both the bass and treble sides. The template must be unclamped after the treble side is cut and repositioned to cut the bass side. Align these off-center cuts slowly and carefully!