Shaping the Sides For Back Plate:
The diagram above indicates the Guitar Side Template that I made for the Dreadnought Guitar offered at Georgia Luthier Supply. Note that there is a straight side, on the
top, which would be the Guitar Top Plate, and an irregular side, on the bottom, which would be the Instrument Back Plate.
All of our acoustic instrument plans include side templates when will permit you to either pre-shape the side prior to bending or shaping the side post-bending.
After making this template, tape the ends on the head and tail joints of the side. Then carefully tape the top side (the straight side down. Now trace around the back contour with a medium sharpie dry marker to put a heavy line on the side.
GLS Tip #1: It is possible to rough cut the sides to shape prior to bending them too. While it is far easier to mark and trim the contour on a flat surface, you have to use caution to get the side perfectly registered when bending as you have little room for error. Just carefully mark the centerline of the waist on the faces and edges of the sides to be bent so you can monitor them while placing in the bending jig.
Don’t be concerned with using a permanent marker on the wood. This line will be completely cut away during the binding routing process.
Next you can take a sharp Low Angle Plane (I use the Leigh Neilson Low Angle Plane) and cut down the sides to within about 1mm of the marked line.
Finally take a long sanding surface and cut down right to the center of the line. You should block up the side opposite of the sanding surface to get the right amount of crown in the head and tail block. Be sure to spend extra time on the head and tail block areas and get them perfectly contoured.
You will be able to finally sand the sides after installing the lining for the backs.
There are several ways to make a side template. If you only have a letter-sized inkjet printer, the template can be printed out on 2 or 3 sheets of heavy paper. Carefully trim each piece to perfectly align with the others and then tape them together. You should place a straight edge on the straight line of the top to keep it perfectly straight otherwise the back contour will be off. If you want to use it more than for one guitar, you can laminate the template with wide clear adhesive tape, like shipping tape.
Of course if you want the production version of a very durable template, use 1/32″ thick Lexan (Polycarbonite).
GLS Tip #2: Here is how you estimate the proper amount of angle to place on the Sanding Surface. Measure the crown for the back plate on your Guitar Plan. Let’s say it is 5 mm at the highest point. Next double that about and add a block 10 mm thick on the Sanding Surface opposite the sanding end. As you are sanding, make sure that the Sanding Surface rides on this block and your crown will be correct.
GLS Tip #3: You will find that cutting the head and tail block carefully to within .5 mm to 1 mm of their final height will save a lot of elbow grease and sanding the end grain of these hardwood block can tack considerable time.