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How to Measure & Bend Tubing

When measuring and bending tubing, it's important to understand how metal reacts as it is bent. The cold bending process, where tubing is not preheated, can twist and distort, leaving you with angles and dimensions that do not match your original plan. To avoid error, always measure your bend points from the center line of the tube, use a jig to prevent distortion or twisting, and compensate for three degrees of spring-back, to ensure the angle and subsequent tubing run follows your plan accurately.

Things You'll Need

Tube bender
Tubing
Scrap tubing
Measuring tape
Angle measure
Permanent marker
Level
Chalk

Instructions

- 1
  Place the scrap tubing and good tubing piece on a workbench against an object that prevents the tubes from sliding. Draw a line along the entire base of each tube, where it touches the workbench, to create a center line mark. Use this mark as a reference point for all your measurements, angle verifications and for identifying any twisting along the tube.
- 2
  Insert the scrap tubing piece into the tube bender and bend it to 90 degrees. Mark the points where the distortion begins and ends on the bend. Slight distortion on the inside of the bend is natural and can be felt with your hand. Mark this point and measure towards the the center line of the tubing section after the bend. This measurement will tell you where you need to begin a bend on the good piece of tubing.
- 3
  Mark the good tubing at the initial bend point. Insert the tube into the tube bending machine, with the center line on the outside of the bend. Bend the tube to the desired angle, over bending by exactly three degrees. When a tube is bent, it will spring back three degrees. So as a general rule of thumb, bend a 90-degree angle to 93 degrees or a 65-degree angle to 68 degrees.
- 4
  Hold your angle measure on the outside of the bend and confirm the desired angle is achieved. If not, bend it again until the proper angle is reached.
- 5
  Place the good tubing into a tube jig to complete complex bends. The jig will save you time by requiring little or no measuring. To use a jig, first bend the pipe, then place the pipe in the jig to ensure it's fitting the jigs dimensions. Alternatively, you can clamp a wooden jig to a workbench and bend the tubing around the jig -- an ideal method for large radius bends and portable tube benders.
- 6
  Place tube circuits (tubes bent into a "U" shape) with the U pointing up. Place the level on the top side of the pipe to ensure the two open ends are the same length. If not, the U will not be level, in which case the shorter side's angle will need to be re-bent closer the to U's center, elongating that side.
- 7
  Draw chalk outlines on a clean ground surface, for large or complex tube bends. Bend your tubes to match these outlines and measurements. This method is commonly used for building roll cages and tube frames that require multiple, symmetrical bends.

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