Brian's Guitar from Conception to Birth or How to Build a Guitar in 62 Easy Steps!
8 Make the Control Cavity Cover
The easiest way to do this is to use the same template you used to cut the control cavity cover ledge earlier on the back of the guitar. The template was made to the exact size and shape of the final product. So using a little math (remember that class) you can come up with a way to use guide bushings to repeat the exact shape. Our cover will be made from mahogany to match the body panel, but this process will work with whatever material you choose; the concept is the same.
Plane the wood down to just barely over the exact thickness your ledge is on the body. This will leave a little to sand off flush later. You’ll be making a template using your original control cavity cover template. Secure a piece of 1/4" MDF onto a scrap sheet of plywood with double-sided tape as you will be cutting all the way through. Remember to stick a piece of tape directly under your cutout so it doesn’t catch the bit and go flying when it is released. Mount your original template over the MDF with double-sided tape. Setup your router with an 1/8" bit with a 3/8" OD bushing. This will cut the same shape, but it will be 1/4" smaller all the way. Now rout around the perimeter being careful not stray inside fouling the template you’re making. Make a couple of light passes to release the new template. Mount this new template onto your final material using double-stick tape. Remember to stick a piece of tape directly under your cutout so it doesn’t catch the bit and go flying when it is released. Install a 5/8" OD guide bushing in the router, This will produce a 1/4" offset, which happens to be exactly the size your template was cut shy in the previous step resulting in an exact replica of your original shape.
You will need to sand a hair off the edges to fine tune the fit. It shouldn’t be so tight you can’t get it out. Sand and test the fit repeatedly so you sneak up on a fit which allows you to remove the cover plate easily. With a little patience you will get it perfect. You can’t even see a seam in the photo.
Cut the cavity cover from your paper pattern and position it onto the actual cover to transfer the mounting screw locations with an awl. Use a 1/16" drill bit to make pilot holes all the way through the cover. Now place your cover onto the guitar. Use these holes to locate and drill the holes into the guitar body. Only drill a very shallow hole into the body (about 1/16" deep). We’re just locating the holes at this point.
Remove the cover plate and you will see exactly where to drill deeper and wider for the mounting screw pilot holes. I’m using threaded inserts which will never strip out, but the process is the same if you’ll be screwing yours directly into the body. Gauge the depth of the threaded inserts and add 1mm to the depth so you don’t bottom out the inserts. Mark your drill bit with masking tape and drill as straight in as you can. A drill press would make this easier. Brass inserts are very soft, so thread them into the holes very carefully with a hand screwdriver. Drill the holes in your cover plate slightly larger than the screw's shank and countersink for the screw heads. This is easy if you have a drill/ countersink bit. Mount your cover plate and lightly tighten the screws. Notice I said, “lightly”. You don’t need to torque these screws down. Sand the cover plate perfectly flush to the body.