You can bend pipe and tubing in one of several methods, depending on what you plan to use the bent pipe or tube for. The problem in bending pipe is figuring out where and how much to bend the pipe. While many bending tools come with a set of instructions for figuring out such things as bend allowances and bend deductions, they are often written in a complex manner and assume a knowledge of mathematics that intimidates many users. While it’s not possible to completely eliminate the math, it is possible to plan how to bend a piece of pipe in such a way that figuring the bending angle is simplified and so that the only math needed is simple arithmetic. The method described below is not simple, but with practice, you can master it.
Selecting a Bending Tool
Choose the right bending tools for your needs. There are 6 main bending methods. Each is best suited to a particular type of pipe.
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.
Making a Right Angle Bend
Bend a test pipe at a 90-degree angle. Not only will this familiarize you with how much force you need to apply to operate your bender, but this pipe will serve as a reference for future bends.
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.
Find the place where the bend in the pipe starts. You should see or feel a small flat spot or distortion at the place where the bend starts and where it ends.
Mark the ends of the bend with a permanent marker. Draw the line completely around the pipe.
Lay the pipe against the square again to find the length of the pipe in the bend.
Note the place on each side of the square where the pipe’s markings touch. These should be the same distance from the inside corner of the square. Add these lengths together.
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).
Find the place on your bending die where the bend begins. Place the bent tube back in your bender with the die used to bend it and note where on the die the mark on the pipe lines up. Mark this place with a dot of paint or by notching the metal with a file.
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 le