BIZOMAT MAKEOS · Fabrication
Tube Bend Developed Length
What centreline length follows from these straights and bends?
Sum straight tangent lengths and centreline arc lengths for repeated equal-radius tube bends.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Centreline bend radius | mm | Radius to tube centreline, not inside radius or die outside diameter. |
| Direction change per bend | ° | Direction change per bend; 90° is a right-angle turn and 0° is straight. |
| Number of identical bends | bends | Bends sharing the same radius and direction change. |
| Total straight tangent length | mm | Sum of straight centreline lengths between tangencies and ends, not theoretical sharp intersections. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Centreline bend radius
- What it is
- The bend radius measured to the centreline of the tube, the radius the tube axis follows around each bend.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each bend’s arc length is directly proportional to this radius.
- Get it right
- Not the inside radius or die diameter; centreline radius is the inside radius plus half the tube outside diameter.
What this means: Direction change per bend
- What it is
- How much the tube changes direction at each bend: 90° for a right-angle turn, 180° for a U-bend.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 360°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Arc length per bend is directly proportional to the angle.
- Get it right
- Use the direction change, not the included angle between legs; a 45° offset bend changes direction 45°.
What this means: Number of identical bends
- What it is
- The number of bends in the tube that share the same centreline radius and direction change.
- Units and format
- Enter a number in bends: bends. The form accepts 0 bends to 1000 bends. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 bends as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Total arc length is directly proportional to the number of bends.
- Get it right
- Bends with a different radius or angle must be calculated separately.
What this means: Total straight tangent length
- What it is
- The total length of all straight sections of the tube centreline, measured between bend tangent points and to the tube ends.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 400 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It adds directly to the developed length.
- Get it right
- Do not use sharp-corner intersection dimensions from the drawing; they double-count part of each bend.
Method and formulas
- One arc = radius × angle × π/180. Total = total straights + bend count × one arc.
- Example: two 90° bends at 50 mm centreline radius add 157.079633 mm to 400 mm straights, giving 557.079633 mm.
- For different radii, calculate each arc group separately and add each contribution once to the common straight total.
Limitations
- Centreline geometry excludes stretching, thinning, ovality, springback, clamp allowance and trim.
- No minimum bend radius or forming feasibility is established.
- Bend intersections and three-dimensional collisions are not checked.
- Default values are worked examples, not recommended settings or material properties.
Typical uses
- tube development
- centreline arc
- bend allowance
Who it is for
- Tube fabricators
- Mechanical designers
- Estimators
What you get
- Arc per bend
- Total arc length
- Geometric developed length
Interpreting the result
- Confirm tangent locations on the drawing or CAD model.
- Use process trials and the machine method to release the production cutting length.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1382–1383. Topic reference; implementation and examples are original, and no source tables are reproduced.
- Method: circular arc length in radians plus straight centreline lengths.
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