From Power Nation Garage
When your project requires a little bit of tube bending, you’ll want to calculate the cost of the materials you’ll need.
To accurately calculate this, you’ll need to know how many inches of tube it takes for each degree of bend. This varies by the bender you use, the die in your bender, as well as the tubing.
First, you’ll want to mount the tube in the bender with the correct size die and set your pre-load. Then, mark a reference line at the follower on the tube. Starting at your reference mark, draw a line every 1″ down the tube for at least a foot. Be sure to mark which end is your starting point. Re-mount the tube making sure you line up your reference mark with the follower. Set your pre-load and zero out your degree-bend indicator on the bender.
Start bending the tube, stopping every 10-degrees of bend to make a new mark on the follower. You may want to use a different color marker so as to not get your marks confused.