How to Bend Tube and Pipe
Time Required: Under 2 hours
Metal fabrication requires care and precision, but learning how to bend tube and pipe can give you more control over your projects. The more advanced bending machines for pipe and tubing may be more cost effective in commercial or industrial applications, but simpler pipe and tube benders can find a prized place in the workshop.
Rigid metal pipe and tubing tend to be made of copper, steel, stainless steel or aluminum, but are not the same thing.
- Generally, tube is measured by the outside diameter while pipe is measured by the inside diameter, so pipe may appear thicker than tubing of the same measurement. For example, piece of one-inch pipe will seem to have a greater diameter than a piece of one-itch tubing.
- When bending tube or pipe, use the tool designed for the right item and the right size. Do not use a tube bender on pipe or vice versa.
- The center line radius, or CLR, is the radius down the center of the tube and is the standard way to measure a bend. The smaller the CLR, the sharper the bend; the larger the CLR, the more gradual the bend.
- The bend radius measures the inside curvature and indicates the minimum radius one can bend a pipe or tube without kinking or otherwise damaging it. The greater the flexibility of the material, the smaller the bend radius.
- The die (sometimes called the “shoe”) of a pipe bender is the curved form around which the pipe bends.
- Springback is the tendency of a pipe to revert to towards its original shape after bending. You may need to bend slightly further than your target to compensate for springback, based on the kind of material and the thickness of the tubing wall. Copper tubing bending often sees less springback than other materials.
There are multiple methods of bending to meet the requirements of pipe and tubing of different sizes and materials.
- Compression bending involves holding one end of a tube in place and bending it around a die or other kind of former. The simplest applications involve bending by hand, such as bending a copper tube around your knee, as well as using simple manual pipe benders and tube benders.
- Draw bending tends to be more effective on tubing with thicker walls or made of stiffer material such as steel. Rotary draw bending can ensure tight radii and bend pipe for heavier conduit, handrails, trailer frames, ornamental iron and car chassis. A bending mandrel can be inserted in the pipe to prevent kinks or other damage.
- Ram-type bending uses a hydraulically driven ram that forces a tube against pivot blocks or rollers. Also called incremental bending, this is one of the oldest, simplest and least-expensive methods and often used for light-gauge metal such as electrical conduit.
- Roll bending often uses three rolls in pyramid shape that roll the pipe through the mechanism as the top roller pushes down to bend the pipe. Tube rollers are often used for large bends in pipe or tubing workpieces in construction.
- Induction bending involves placing a heat induction coil around a tube at the bend point. The user heats the coil and applies pressure to bend the softened tube to the desired angle.
- Hot bending involves applying heat (by a tool such as a blowtorch) to soften a portion of metal tube held in place with a clamp, then bending it to the desired angle.
When bending tube or pipe, the interior wall of the bend becomes more compressed and thicker, while the exterior wall becomes stretched and thinner. To determine how long a piece of tubing you need and to make sure it achieves the correct shape, use this method to create a 90-degree reference bend.
- Begin by estimating the needed length of tube or pipe.
- Mark the beginning and end of the desired bend, along with a longitudinal line on the side of the pipe opposite to the chosen bend direction (i.e., the exterior side).
- Bend a test pipe 90 degrees to use as a reference.
- Check the angle of the pipe by laying it against a carpenter’s square with the outer bend facing the corner.
- Find and mark the distorted places where the bend begins and ends with a permanent marker. They should be the same distance from the inner corner of the square.
- Measure the distance between the beginning and end of the pipe by adding the distances on the x and y axis. For instance, if they’re both six inches from the end of the square, the length of the bent section of pipe will be 12 inches.
- Place the 90 degree reference tube back in the bender with the matching die. Note the places on the die where the bend begins and ends on the tube and mark them. These will be the reference points for future 90-degree bends.
- If the pipe springs back after the initial bend, bend a second time using the reference point.
Tip: The formula for the length of bend (or the arc of the bend) is L = 0.001745ur, in which u = the angle of bend in degrees and r = the radius of bend in inches.
- Choose the bender or appropriate die size based on the size of pipe to be bent.
- Set the device's adjustment dial based on the desired radius and overall number of degrees required in the bend (for example, 90 degrees). A digital angle gauge can be used to track the angle.
- Swing up one of the tube bending arms to place the tube in the die, keeping the reference marks visible.
- Align the mark for the start of the bend with the leading edge of the die. The center of the bend should correspond with the center of the die.
- Lower the second arm to hold the tube in place. Many devices include a latch.
Tip: Before using a manual bender, try packing the tube with sand, which will ensure the bent tube will hold its round shape evenly without kinking or buckling.
- Grip the roll support arm and bring it down until the tube reaches the desired degree mark on the bending die.
- Lift the roll support arm, disengage the tube from the die and remove the finished tube from the bender.
Tip: When bending pipe with high wall thickness and you're new to process, consider holding the pipe in place with a vise.
Pipe bending can be a challenge and require an investment in tooling, but opens up new possibilities for an ambitious fabricator.