What is "D of Bend" in Tube Fabrication?

What is D of bend?

Tube fabricators sometimes indicate the centerline radius using D of bend.

We say it by speaking three words: "D of bend".

Some tube fabricators also say "D factor" to mean the same thing.

It is a ratio calculated like this: D of bend = Centerline Radius / OD

How Is It Used?

FOR FABRICATORS

• The D of bend value helps fabricators know if the radius is tight or large compared to the OD.
• It serves as a general guide for how difficult it will be to create a quality bend.
• It helps fabricators know what kind of tooling will be necessary to achieve the bend. It is useful, therefore, in building quotations for customers.
• It is common for fabricators to share the lower limit of their D of bend capabilities with customers.

FOR DESIGNERS

• It is helpful to designers as a limit for what is practical in choosing radii.

Example Values

In most applications, a lower D of bend valued radii is less complex and therefore less expensive.

• D of bend = 2.00 or greater is generally considered not difficult.
• D of bend = 1.50 is moderately difficult.
• D of bend = 1.00 is difficult.
• D of bend = 0.75 is very difficult and much more expensive.

Notes

• D of bend values at 1 and below are possible - but are rare and require special benders that can press material into the bender's dies. (Most call this "carriage boost".)
• Other variables, like wall factor, impact what is difficult. Wall factor = OD / Wall Thickness

Example Models