A brake is an essential tool for working with sheet metal. Professional siding crews and heating/ventilating/air conditioning (HVAC) technicians may work with metal brakes on a daily basis, and can justify purchasing a metal brake as a legitimate cost of doing business. Unfortunately for the do-it-yourself type, metal brakes are often expensive, and it is impractical to buy one for use on only a few projects. With some lumber, you can build a brake from wood, that will perform just as well as an commercial sheet metal brake.
Cut two 12 inch pieces out of one of the 2 x 4's. Construct a box 15 inches wide by 8 feet long by gluing together and screwing the 12 inch pieces between two other 8 feet 2 x 4's -- fit the 12 inch pieces flush with the ends of each 8 foot section. Your box should measure 15 x 96 inches long, with the 2 x 4's standing on edge.
Fasten two of the 1 x 8's to the top of the 2 x 4 rectangle by gluing and screwing them down. Make sure no screws are raised above the surface of the 1 x 8's. The 1 x 8's should fit flush with the edges of the box, with the good side up. Make sure you have at least one piece with a straight, square edge facing out. This will become the platform on which you will place the sheet metal -- adjust it to handle whatever length or width of sheet metal you choose).
Cut legs out of the remaining 2 x 4's with which to suspend the box as high as you choose. Attach the legs by gluing and screwing them on the inside edges of the platform.
Fasten the piano hinge on one edge of the remaining 1 x 8, with the pin side of the hinge flush along the good edge of the board. Use 3/4 inch wood screws, and fasten the hinge at least every 3 inches. Measure the width of the hinge, then measure and mark a line on the platform the same distance below the edge of the platform as the width of the hinge (measure from the top of the 1 x 8 with the good edge, and mark your line while pulling a measurement from that edge).
Open the hinge 90 degrees and align the edge of the hinge with the line you marked on the platform. Then, fasten the hinge to the platform every 3 inches with the 3/4 inch screws.
Build braces to attach to the moving part of the brake. Measure in from each end of the "moving" piece of hardwood 2 1/2 feet, and make a mark near the piano hinge. At each mark, attach perpendicular to the hinge and with the length extending away from the hinge, one piece of 2 x 4, 12 inches long. Glue them in place and drive in two wood screws from the top (or metal-contacting side) of the 1 x 8. Brace these pieces diagonally from the other edge of the 1 x 8 with another piece of 2 x 4 cut at with angled ends so that it fits between the 12 inch 2 x 4 and the 1 x 8 (the two pieces of 2 x 4 and the 1 x 8 will form a rigid triangle).
Now, with the piano hinge still bent so that the brake is closed, attach the other 8 foot piece of 2 x 4 to the legs of the brake 9 inches below the top surface (attach it "flat" to the legs so that the 4 inch width faces you). The braces on the moving part of the brake will rest against this 2 x 4 so that the hinge is not damaged, allowing you to slide the sheet metal around on a flat surface.
Attach 2 foot lengths of 2 x 4 at right angles to each angled part of the triangular brace on the moving part. These will serve as handles.
Use the 4 x 4 and pipe clamps to hold sheet metal in place as you bend it.