Soak four sheets of plywood in water for 24 hours. The plywood should be 6-by-2 feet and no thicker than 1/2 inch.
Remove all four sheets of plywood from the water and place them together to form a stack.
Place the stack of plywood on your workspace. You will use this sheet to create a guide to shape your harp spine.
Secure the top portion of the plywood stack with a vise attached to a work table so that it won't move.
Place another vise 3 feet from the first vise. Create a bend in the plywood between the first vice and the second vise of approximately 45 degrees.
Hold the bottom of the plywood in place by securing a third vise at the end of the plywood. The bottom and the top of the plywood stack must be angled so that they line up with each other.
Place nails every 2 inches along the inside and the outside of the plywood to create a bow shape.
Let the plywood dry and sit with the vises and nails in place for 24 hours.
Remove the plywood from the vise, while keeping the nails intact if possible. Apply a generous amount of wood glue between each sheet of plywood, from the top to the bottom. Then, place the bow back into the brace and let the glue set for at least 4 hours or according to the manufacturer's instructions.
Use a rough sandpaper and then a fine-grit sandpaper to smooth the exterior of the plywood.
Nail upholstery tacks every 2 inches starting with the top end of the bow and ending 6 inches before the middle of the bow. Add a series of tacks on the bottom portion of the bow to match the tacks on top.
Tie nylon string to the top and bottom of each tack. The string should wrap around the bottom portion of the bow twice. On the top portion, tie the string directly to the tack without wrapping it around the plywood.
Tune the strings to your desired pitches by increasing the tension of each string to raise the pitch, or decreasing the tension to lower the pitch.