Tube Bending Formulas & Common Terms | Tubular Components Design

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.

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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.

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
   
   

Tubular Components Design Guide

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