The “Eagle 10-20 Rule” for Roll Bending Feasibility
One of the most common questions that people have regarding roll bending is,
“How small or tight of a radius can I bend?” a given profile.
This is an important question for many reasons. What an architect, engineer, or artist can put on paper regarding curved and bent shapes may or may not apply to the material selected and may not even conform to the laws of physics. When it is your task to turn these designs into reality, we have a handy rule-of-thumb that can keep you out of trouble; save time; and will help you to make design recommendations that are more likely to fall within the laws of physics. It is called the “Eagle 10-20 Rule”.
When roll bending any profile, the inside of the radius is compressed and the outside of the radius is stretched. Roll bending feasibility is dependent upon how well a profile can hold up to these forces. The “Eagle 10-20 Rule” is not machine specific but is used to determine if a profile is suitable for roll bending to a given radius with non-heated material.
Part 1: Multiply the material height by 10 to get the minimum diameter that can be rolled.
Material Height x 10 = Minimum inside diameter
It may be possible to roll bend smaller diameters but the effects of material deformation and distortion will be more significant. If the required radius is at or below the calculated minimum inside diameter it is best to physically test the material to determine the results and bend quality.
Part 2: Divide the material height by the material thickness. If the result is greater than 20, the material will fail or distort and is not suitable for roll bending.
Material Height / Material = Less than 20
You can think of a scale of 1 to 20, e.g. 1 being very easy and 20 being very difficult. Profiles which score 15 to 20 may require rolling the part in multiple passes to relieve stresses in the profile or using nylon filler or shot medium to provide additional support to withstand the bending pressures. If the score is high, testing is recommended to determine the resulting roll bending quality and profile aesthetics. Scores that fall below 15 indicate that the profile will be easier to roll bend. Easier means that these profiles will require fewer roll bending passes and will take less time to produce.
If your follow the “Eagle 10-20 Rule” you are more likely to stay out of trouble, save time and money, and work within the laws of physics!