Ram style bending, also called incremental bending, is usually used for putting large bends in light-gauge metal, such as electrical conduit. In this method, the pipe is held down at 2 external points and the ram pushes on the pipe at its central axis to bend it. Bends tend to deform into an oval shape at both the inside and outside of the bend. Rotary draw bending is used to bend pipe for use as handrails or ornamental iron, as well as car chassis, roll cages, and trailer frames, as well as heavier conduit. Rotary draw bending uses 2 dies: a stationary counter-bending die and a fixed radius die to form the bend. It is used when the pipe needs to have a good finish and constant diameter throughout its length. Mandrel bending is used to make stock and custom exhaust pipes, dairy tubing, and heat exchanger tubing. In addition to the dies used in rotary draw bending, mandrel bending uses a flexible support that bends with the pipe or tubing to make sure the pipe interior isn’t deformed. Induction bending heats the area to be bent with an electric coil, and then the pipe or tube is bent with dies similar to those used in rotary draw bending. The metal is immediately cooled with water to temper it. It produces tighter bends than straight rotary draw bending. Roll bending, also called cold bending, is used whenever large bends are necessary in the pipe or tubing, such as in awning supports, barbecue grill frames, or drum rolls, as well as in most construction work. Roll benders use 3 rolls on individual shafts to roll the pipe through as the top roller pushes down to bend the pipe. (Because the rolls are arranged in a triangle, this method is sometimes called pyramid bending. ) Hot bending, in contrast, is used considerably in repair work. The metal is heated at the place where it is to be bent to soften it.
To check the angle of your pipe, lay it against a carpenter’s square with the outer bend facing the corner of the square. Both ends of the pipe should just touch the square’s sides and run parallel to them.
If the markings on each end of the pipe bend touch the square at 6 inches (15 cm) from the inside corner of the square, the total length of the bent section of the pipe is 12 inches (30 cm).
If you have more than one die (for different diameters of pipe), make a test bend for each die, as each diameter will require a different amount of metal to make a 90-degree bend. Once you know how much pipe is needed to form the bend, you can calculate how long a piece of pipe you need by adding this figure (called the bend deduction) to the vertical and horizontal lengths of the pipe.
In this example, the diagonal line connecting the marks on the horizontal and vertical lines is about 14 inches (70 cm) long.
In the above example, the vertical portions of the roll bar will each be 40 inches (100 cm) long, the diagonal portions will each be 14 inches (70 cm) long, and the horizontal portion will be 40 inches long. The total minimum length of pipe will be 40 + 14 + 40 + 14 + 40 inches (100 + 70 + 100 + 70 + 100 cm), or 144 inches (440 cm) long.
You may also want to mark the direction of your bends by putting arrows on the pipe pointing outward.
To ensure your bender is set to the correct angle, you can prepare a reference tool of 2 flat pieces of metal whose ends are attached to a pivot. Bend this tool to the angle indicated on your frame, and then match the bending angle of your bending tool to this angle. After making each bend, lay the pipe against your frame to check that the angle of the bend is correct.
