Preparing the Back
Before the back (or top) can be glued onto the sides, the scalloped ends of the braces need to be cut down to a uniform height (0.90" - 0.110"). Likewise, the lining needs to be notched to accept the brace ends. The objective is to have the depth of the notch in the lining the same dimension as the height of the brace end (or minutely more). The photo above shows the notches that have been cut in the lining and the side to accept the back braces. Below is a photo of the back braces, scalloped ends which have been cut to a uniform height.
OK, I'll tell you... at the end of this month's journal. First, I would like to give a shout out to the good folks of Beijing, China who are regularly a significant percentage of the visitors to this website every month. I hope that you will visit Woody's shop someday.
Also, as we will be talking about the back of the guitar, I would like to insert a note about the geometry of the back which I just glanced over rapidly last month. WJS (Wooden J Strings) guitars are built with a barrel contour to the back. Most guitar makers do this both for strength and (I believe) a deeper acoustic resonance. To achieve this shape, the wooden plate which is the back must bend in two directions.
Which of these photos is of Bob Dylan and which is Woody Guthrie?
The top now needs to be prepared the same as the back was, i.e. the brace end scallops must be cut to a uniform height, and the lining must be notched to accept the 12 brace ends that intersect with the sides. First, draw the silohoutte of the partially-finished box onto the underside of the top (i.e. the top is laying on its face and the box is laid on top of it). Then cut out the top leaving 5-6 mm all around for good measure. It's nothing to rout this off later.
Arching of the back is accomplished by contouring the bottom side to the braces which run across the back, and by tapering the back-side edges of the guitar from the butt to the neck. The top-side edges of the sides are flat. The sides are tapered before they are bent.
The actual box is used to trace out the silohoutte because, try as one may in a small shop, things are not always square and symmetrical to the center line. It is a real problem to cut the top down to size sometime last week, and find out this week that it is a couple of millimeters too small. It happens.
It's a good idea, therefore, to control the shape of the guitar as you are gluing on the top and back plates. Things get asymmetrical without asking you. To do this, I keep the guitar in the mold (which I know is symmetrical) when I am getting ready to glue on the top or the back. That way, minor tweaks are possible to bring things back in line if needed.
Closing the Box (back first method)
A very satisfying day is the day that the top and back are finally glued to the sides of the box. The gluing of the top usually takes place one day, and the following day the back is glued. It really doesn't make a lot of difference which is glued on first, the top or the back. Glue drips, however, are very difficult to clean up once the box is closed. The back-to-side glue joint will be seen by anyone looking inside the sound hole. I am, therefore, gluing the back on first and will clean up any drips or squeeze out before gluing on the top.
It can be a challenge to have all of the brace ends align perfectly with the notches in the lining. Sometimes the notch needs to be widened. This is not a big deal but the back strip must also be cut so that it abuts both the neck block and the tail block. Do this first and then mark and cut the notches for the brace ends.
Manufacturers have precise templates and laser cutting machines that are precise down to a thousandth of an inch. Don't be surprised if you have to work with your hand-tooled lining joints just a bit. Before glue, clamp the back in place and make sure that the entire perimeter is in good contact with the lining. Do not let the back strip reinforcement get under either block. That would not be good.
Glue drips and messy glue joints can be avoided by not using too much glue to begin with. An even spread of glue can be achieved by applying with a cheap 1" paint brush. I prefer to use Titebond original and leave the guitar in clamps, and the mold, at least overnight, preferably 24 hours.