Tube Bending Formulas & Common Terms | Tubular Components Design

Dark steel tubes bent into a curved shape

This guide to tube bending formulas will help you optimize your tubular components. Download the full guide here for a complete list of dos and don'ts.

If you have any questions about designing for tube bending, feel free to contact us directly.

Tubing Bending Formulas & Common Terms


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common terms & Constants

  1.  Centerline Radius (CLR) - the neutral line; will not stretch or compress during bending
  2.  Outer Diameter (OD)  - length and width of tube measured from the outside wall
  3.  "D" of Bend - ratio between CLR and outside diameter
  4.   Wall Thickness (WT) - thickness of tube wall measured in inches or millimeters
  5.  Gauge - thickness of tube wall as a standard integer (0.049" WT = 18 gauge)
  6.  Ovality - difference between max OD and min OD on a bend section
  7.  Inside Bend Radius (intrados) - measurement of the inside curve of a bend
  8.  Outside Bend Radius (extrados)measurement of the outside curve of a bend

 

Common Methods for Defining Tube Shapes

1.  XYZ Method

General method for defining tube shape, based on three-dimensional mathematical planes. Used alongside LRA method to optimize design for production.

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Image from Ercolina CNC

2.  LRA or Bend Data Method

Common method of defining tube shapes when bending is involved. Complements XYZ measurements. Uses three elements to define shape: DBB, DOB, and POB.

L / DBB: distance between bends; where one bend ends and another starts to curve

R / POB: plane of bend; rotational relationship between one bend plane and the next; defined in degrees

A / DOB: angle of bend, measured in degrees

useful equations

  1. "D" of Bend:  CLR / OD

  2. Inside Diameter:  OD - (WT - 2)

  3. Inside Radius:  CLR - (OD / 2)

  4. Outside Radius:  CLR + (OD / 2)

  5. Wall Factor:  OD / WT

  6. Extrados Wall Thinning %:  (Outside Radius - CLR) / Outside Radius

  7. Percentage Elongation at Arc of Bend:  (Outside Radius / CLR) - 1

  8. Ovality:  Max OD - min OD

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