ISO 2768-vL general tolerance and its limits

On the design drawing of a large welded frame or a raw casting, the title block reads ISO 2768-vL. The metrologist has to apply the very coarse class ‘v’ to linear dimensions and the wide class ‘L’ to geometric features.

Applying the ISO 2768-vL general tolerance

Size range (mm)	Very coarse class ‘v’ (mm)	Flatness class L (mm)	Perpendicularity L (mm)
Over 120 up to 400	±1.5	0.6	1.0
Over 400 up to 1000	±2.5	1.0	1.5
Over 1000 up to 2000	±4.0	1.6	2.0

All values are given for the reference environmental conditions of 20 °C.

Linear limits for class v

For an 800 mm raw length with no tolerance of its own under ISO 2768-vL, the allowed deviation is ±2.5 mm. The size must lie between 797.5 mm and 802.5 mm. To compare with medium tolerances, read our article on the ISO 2768-mK tolerance at 250 mm.

The wide geometric specifications of class L

Class L allows large distortion (e.g. 1.6 mm of flatness over 1.5 metres), suited to raw parts of heavy frames.

Example: inspecting a welded cross-member

A 1200 mm cross-member dimensioned under ISO 2768-vL. Laser distance meter reading: 1204.8 mm. 1. Class v, 1000–2000 mm range: ±4.0 mm. 2. Allowed limits: [1196.0 mm; 1204.0 mm]. Verdict: the measured size (1204.8 mm) exceeds the upper limit by 0.8 mm. The cross-member does not conform.

Classic pitfalls in applying class vL

The first pitfall is applying class vL to surfaces that are machined afterwards. The second is distortion while the part is handled by crane. The third comes from the wrong ambient temperature. To manage your dimensions, use CoteCote and its detection module.