LIMITS, FITS, ALLOWANCES AND TOLERANCES

Production of exact size of a feature is impossible to achieve due to following reasons;

• Variations in properties of material being machined

• Inaccuracies of production machines

• Operator and environmental dependant uncertainties

For satisfactory function of a part, exact size of a feature is not necessarily required.

A part can fulfill the design intent functions when the deviation of feature size remains in established boundaries. Maximum and minimum permissible sizes (established boundaries) within which the actual size of a feature lies are called limits of size.

Another function of establishment of the boundaries is to have interchangeable parts which are so nearly identical and fit into any assembly of the same type.

Limits, fits and tolerance calculators have been designed to calculate the limits and fits according to ISO 286-1 (2010), ISO 286-2 (2010) ,ANSI B4.2 (1978), ANSI B4.1-1967 (R2004) standards which are based on metric and inch units.



CALCULATORS & SUPPLEMENTS
Calculator Usage
ANSI limits and fits calculator Calculates limits, fits and tolerances according to ANSI B4.1 -1967 (2004) standard.
Preferred tolerances and fits charts (ANSI) Preferred tolerances and fits given in ANSI B4.1-1967 (R2004) standard are summarized
Limits, fits and tolerances calculator (ISO system) Calculates limits, fits and tolerances according to ISO 286(2010) and ANSI B4.2 (1978) standards.
Preferred fits and tolerances charts (ISO) Preferred tolerances and fits advised by ISO 286-1 (2010) and ANSI B4.2 (1978) standard are given to help user about the selection of fit. Whenever possible, selection of tolerance class shall be done among these tolerances to avoid too many numbers of tools and gauges.
Interference (press & shrink) fit calculator Calculates the press fit force, required temperatures for shrink fit, fit stresses and other parameters necessary for interference fit design
Formulas for press fit / shrink fit calculations Formulas for the calculations of press and shrink fit parameters. 

Reference:
  • IS0 286-1 (2010) Geometrical product specifications (GPS) - ISO code system for tolerances on linear sizes - Part 1: Basis of tolerances, deviations and fits
  • IS0 286-2 (2010) Geometrical product specifications (GPS) - ISO code system for tolerances on linear sizes - Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts
  • ANSI/ASME B4.2 (1978) Preferred Metric Limits and Fits
  • ANSI/ASME B4.1 - 1967 (R2004) Preferred Limits and Fits for Cylindrical Parts