Tolerances
ISO fits, general tolerances, surface finish, and tolerance stacks.
In short: Tolerances
The tolerance calculators determine limits and fits according to ISO 286, general tolerances according to ISO 2768-1, tolerance stacks and roughness values as well as statistical figures such as process capability, measurement uncertainty and sampling plans. They do not replace inspection planning, but quickly show whether a requirement can be manufactured and inspected with the intended process.
Frequently asked questions about Tolerances
What does a fit such as H7/g6 mean?
Capital letters denote the tolerance class of the hole, lowercase letters that of the shaft, and the number the IT grade according to ISO 286. H7/g6 is a clearance fit: the hole starts at the nominal size and the shaft lies just below it. At 20 mm nominal size the clearance is 7 to 41 µm.
When do general tolerances according to ISO 2768 apply?
They apply to dimensions without an individual tolerance when the drawing refers to the standard, for example with ISO 2768-m. Part 1 defines permissible deviations for linear and angular dimensions in the classes f, m, c and v. For a 50 mm linear dimension, class m allows ±0.3 mm.
How do you calculate a tolerance stack?
Arithmetically (worst case), all individual tolerances are added; the result is safe but often unnecessarily tight. Statistically, the root of the sum of squares is used and a small probability of exceeding the limit is accepted. Four tolerances of ±0.1 mm give ±0.4 mm arithmetically and ±0.2 mm statistically.
What do Cp and Cpk tell you?
Cp compares the tolerance width with the process spread of six standard deviations; Cpk also considers how far the mean is from the nearest limit. Cpk ≥ 1.33 is a common requirement; at Cpk = 1.0 the spread just reaches the nearest limit.