If you use a Go-Board Gluing Tool (and you should), I would advise that you make arched molds to glue up your back bracing.
You will need to make a mold for each of the different back contours that you are using. This will greatly improve your glue-up efficiency time and if you plan to make multiple instruments, it is a real time saver.
Arch Mold Advantages:
You can glue-up your arched guitar back plates without the use of this Arch Mold, but you will need to shim the back with tapered wood splices from both sides, and locate them at each brace. This both takes a lot of time and it is difficult to obtain the best results.
Other methods include making dished molds, which is quite a chore unless you have a CNC guided router machine – and not many of us have access to one of those! Also, I am quite often asked with a arch mold you only from an arch in one direction, that is parallel to the brace direction. This is simply addressed in that when fitting the back to pre-formed sides made from our Side Templates, the back easily conforms to the arch from front to back of the instruments without additional bending or preparation.
Tools & Materials:
Battery Operated Drill
Scrap Wood 1″ x 2″
(2) Pieces of 1/4″ or 1/8″ Hardboard
1-5/8″ Drywall Screws
Bessey Bar Clamps
Making the Mold:
You can probably make one of these molds in a few hours, if you have the right tools (listed above). You can use hand tools as well, but the process will take more time.
First: Start out by cutting your struts to size on the Table Saw. Cut them about 1/4″ higher than you want the final height of the mold, to allow for easier sawing on the Band Saw.
Second: Take the Back Brace Template you will be using and center it on the struts. Trace the cutting contour of the brace onto each strut.
Third: Cut the contour on the Band Saw or a Scroll Saw. If you are experienced with the Band Saw, you can cut right to the line and not even have to touch up the cut edge. If not, cut about 1mm from the line and sand right to the center of the line on the Stationary Belt Sander with a 90 degree fence installed. Also, if you want to, the struts can be stacked and screwed together for greater accuracy from strut to strut and this saves a lot of time.
Fourth: Size the Hardboard properly to the dimension you need for your mold. Set the struts into position on the 1/4″ hardboard backing. Clamp in place and drill screw pilot holes and counter sunk screw heads with a Tapered Countersink Drill Bit. Do this with each strut, carefully marking its position, clamping a drilling.
Fifth: Apply glue to the strut bottoms, place them in position, clamp and secure with the screws. Let dry for an hour.
Sixth: Size the hardboard Mold top, clamp into position to follow your arch. drill out the pilot holes and counter sink holes for the screws. Remove the hardboard and place glue on the strut tops. Clamp into position and screw into place. Let dry overnight.
GLS Tip: If you cannot find 1/4″ smooth hardboard, you can use pegboard as a substitute. The advantage is that is bends a bit easier. Also is you have a deep arch and bending proves to be difficult, turn the hardboard over and cut relief cuts on the table saw about 1/2″ apart and 3/4 of the way through the hardboard. You will find the board will bend smoothly and effortlessly. Alternately use 1/8″ hardboard for very easy bending results.