⌢ L Developed length
Developed length · Indicadores dimensionales · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Developed length 287 on flat pattern” states a developed length requirement.
What controls
The actual length of the material laid out flat before forming, i.e. what the part measures as a flat blank before bending or rolling. It does not equal the sum of the outside dimensions of the formed part, because at each bend the material on the outside stretches and the material on the inside compresses, and the length that is preserved is that of an intermediate fiber (the neutral axis). That is why the flat pattern depends on thickness, bend radius and process, and why it is a manufacturing value, not a functional dimension of the finished part.
How to verify
On the flat blank, direct measurement with a tape measure, calipers or comparison against a template before bending. After forming, the developed length can no longer be measured directly: what gets checked are the dimensions of the formed part (flanges, angles, distances between bends) with calipers, protractor or template, and on complex parts by CMM. The real validation of the flat pattern is the test piece.
Common mistakes when interpreting it
- Calculating the flat pattern by adding up the outside dimensions of the formed part.
- Using generic bend allowance values without validating them with your own tooling and material.
- Treating the developed length as a dimension to inspect on the finished part, when it can only be measured before forming.
How to get it in the workshop / if it comes out of tolerance
It is the dimension sent to laser cutting or punching: if it is wrong, every part comes out wrong even if the bending is perfect. Bend allowance values depend on each shop's specific tooling and material, so validate them with a test piece instead of trusting a catalog value. And check the grain direction of the material if the drawing calls for it, because bending against the grain can cause cracking.
Formed parts that consistently come out short or long by the same amount: the flat pattern is miscalculated; correct the bend allowance using the test piece data. Differences between bends on the same part: different bend radii or worn tooling. And if the material varies from lot to lot (thickness or hardness), the flat pattern changes: revalidate before releasing the batch.
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