You can shape sheet metal into flashing, a stoveside heat shield, or squirrel guards. Flat bar stock can be transformed into custom braces to stiffen that wobbly picnic table and brackets to support your hummingbird feeder. Although the blades and bits are often different, cutting and drilling metal is similar to woodworking. But bending metal requires its own techniques.
It’s easy enough to bend sheet metal, whether it’s steel, aluminum, or brass; the trick is getting the bend where you want it and forming a sharp corner. You can clamp a sturdy piece of wood that has a crisp, straight edge at the bend point, sandwiching the metal between the block and your work surface. Pull up on the free end of the sheet and, using a mallet, tap the bend area tightly against the block. To sharpen the corner further, hold a scrap block against the metal and tap on it. For a long bend in sheet metal—say, to customize a length of flashing—replicate a metal brake (the folding tool the pros use): clamp the sheet with a full-length batten of wood or bar stock on top, overhanging the edge of a workbench at the bend point. Clamp a second batten on the underside of the metal at the same bend point, then pivot the bottom batten upward to establish the bend.
Bending flat stock
Cold-bending mild steel is easy with stock up to 3/16″thick and 11/2″ wide, although you can bend thicker material cold with enough leverage. Clamp the steel in a vise at the bend point, then pull it toward you. You can leave the bar overlong and cut it to length after bending, or slip a pipe over the end to gain greater leverage. Even Vise-Grips, locked onto the end, will add leverage. You can also apply persuasion with hammer blows close to the bend. To square up a bend to 90°, reclamp the piece sideways in the vise and hammer the outside of the bend against one end of the vise jaws.
With flat stock thicker than 3/16″, you’ll likely need some heat to bend it. (Heat also makes it easier to form a sharp corner.) Metalworkers use oxyacetylene torches, but you can make do with a propane or propylene plumbing torch. Wear leather work gloves and eye protection, and work outdoors if you can. Mark the bend point by filing a notch in the edge of the stock. Then heat the area near the bend. When it’s cherry red, quickly place it over a corner of the vise anvil and hammer to get the angle you want.
To make a radiused bend, cold or hot, clamp the stock in a vise over a piece of metal pipe with the radius you want, and pull or hammer the metal around the pipe.
Pro Tip: To crimp the end of a downspout pipe (or steel or aluminum duct) without special crimping pliers, use ordinary needle-nosed pliers. place the jaws of the pliers as deep as they will go over the edge of the pipe and rotate them slightly, twisting the metal just a touch. Repeat all the way around, and you’ll get a neat reducing crimp that will slip easily into another length of pipe.